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Merge tag 'rfds-for-linus-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 RFDS mitigation from Dave Hansen:
"RFDS is a CPU vulnerability that may allow a malicious userspace to
infer stale register values from kernel space. Kernel registers can
have all kinds of secrets in them so the mitigation is basically to
wait until the kernel is about to return to userspace and has user
values in the registers. At that point there is little chance of
kernel secrets ending up in the registers and the microarchitectural
state can be cleared.
This leverages some recent robustness fixes for the existing MDS
vulnerability. Both MDS and RFDS use the VERW instruction for
mitigation"
* tag 'rfds-for-linus-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
KVM/x86: Export RFDS_NO and RFDS_CLEAR to guests
x86/rfds: Mitigate Register File Data Sampling (RFDS)
Documentation/hw-vuln: Add documentation for RFDS
x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set
Add the documentation for transient execution vulnerability Register
File Data Sampling (RFDS) that affects Intel Atom CPUs.
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Step 5/10 of the namespace unification of CPU mitigations related Kconfig options.
[ mingo: Converted a few more uses in comments/messages as well. ]
Suggested-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ariel Miculas <amiculas@cisco.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231121160740.1249350-6-leitao@debian.org
there are some significant changes nonetheless:
- Some more Spanish-language and Chinese translations.
- The much-discussed documentation of the confidential-computing threat
model.
- Powerpc and RISCV documentation move under Documentation/arch - these
complete this particular bit of documentation churn.
- A large traditional-Chinese documentation update.
- A new document on backporting and conflict resolution.
- Some kernel-doc and Sphinx fixes.
Plus the usual smattering of smaller updates and typo fixes.
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Merge tag 'docs-6.7' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"The number of commits for documentation is not huge this time around,
but there are some significant changes nonetheless:
- Some more Spanish-language and Chinese translations
- The much-discussed documentation of the confidential-computing
threat model
- Powerpc and RISCV documentation move under Documentation/arch -
these complete this particular bit of documentation churn
- A large traditional-Chinese documentation update
- A new document on backporting and conflict resolution
- Some kernel-doc and Sphinx fixes
Plus the usual smattering of smaller updates and typo fixes"
* tag 'docs-6.7' of git://git.lwn.net/linux: (40 commits)
scripts/kernel-doc: Fix the regex for matching -Werror flag
docs: backporting: address feedback
Documentation: driver-api: pps: Update PPS generator documentation
speakup: Document USB support
doc: blk-ioprio: Bring the doc in line with the implementation
docs: usb: fix reference to nonexistent file in UVC Gadget
docs: doc-guide: mention 'make refcheckdocs'
Documentation: fix typo in dynamic-debug howto
scripts/kernel-doc: match -Werror flag strictly
Documentation/sphinx: Remove the repeated word "the" in comments.
docs: sparse: add SPDX-License-Identifier
docs/zh_CN: Add subsystem-apis Chinese translation
docs/zh_TW: update contents for zh_TW
docs: submitting-patches: encourage direct notifications to commenters
docs: add backporting and conflict resolution document
docs: move riscv under arch
docs: update link to powerpc/vmemmap_dedup.rst
mm/memory-hotplug: fix typo in documentation
docs: move powerpc under arch
PCI: Update the devres documentation regarding to pcim_*()
...
The SRSO default safe-ret mitigation is reported as "mitigated" even if
microcode hasn't been updated. That's wrong because userspace may still
be vulnerable to SRSO attacks due to IBPB not flushing branch type
predictions.
Report the safe-ret + !microcode case as vulnerable.
Also report the microcode-only case as vulnerable as it leaves the
kernel open to attacks.
Fixes: fb3bd914b3 ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/a8a14f97d1b0e03ec255c81637afdf4cf0ae9c99.1693889988.git.jpoimboe@kernel.org
Moves the description of the best effort mitigation mode to the table of
the possible values in the mds and tsx_async_abort docs, and adds the
same one to the mmio_stale_data doc.
Signed-off-by: Takahiro Itazuri <itazur@amazon.com>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230901082959.28310-1-itazur@amazon.com
Add a note about the dependency of the User->User mitigation on the
previous Spectre v2 IBPB selection.
Make the layout moar pretty.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230809102700.29449-4-bp@alien8.de
Most of the index.rst files in Documentation/ refer to other rst files
without their file extension in the name. Do that here too.
No functional changes.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230809102700.29449-2-bp@alien8.de
* Add Base GDS mitigation
* Support GDS_NO under KVM
* Fix a documentation typo
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Merge tag 'gds-for-linus-2023-08-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86/gds fixes from Dave Hansen:
"Mitigate Gather Data Sampling issue:
- Add Base GDS mitigation
- Support GDS_NO under KVM
- Fix a documentation typo"
* tag 'gds-for-linus-2023-08-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
Documentation/x86: Fix backwards on/off logic about YMM support
KVM: Add GDS_NO support to KVM
x86/speculation: Add Kconfig option for GDS
x86/speculation: Add force option to GDS mitigation
x86/speculation: Add Gather Data Sampling mitigation
vulnerability on AMD processors. In short, this is yet another issue
where userspace poisons a microarchitectural structure which can then be
used to leak privileged information through a side channel.
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Merge tag 'x86_bugs_srso' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86/srso fixes from Borislav Petkov:
"Add a mitigation for the speculative RAS (Return Address Stack)
overflow vulnerability on AMD processors.
In short, this is yet another issue where userspace poisons a
microarchitectural structure which can then be used to leak privileged
information through a side channel"
* tag 'x86_bugs_srso' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/srso: Tie SBPB bit setting to microcode patch detection
x86/srso: Add a forgotten NOENDBR annotation
x86/srso: Fix return thunks in generated code
x86/srso: Add IBPB on VMEXIT
x86/srso: Add IBPB
x86/srso: Add SRSO_NO support
x86/srso: Add IBPB_BRTYPE support
x86/srso: Add a Speculative RAS Overflow mitigation
x86/bugs: Increase the x86 bugs vector size to two u32s
These options clearly turn *off* XSAVE YMM support. Correct the
typo.
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Fixes: 553a5c03e9 ("x86/speculation: Add force option to GDS mitigation")
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Add a mitigation for the speculative return address stack overflow
vulnerability found on AMD processors.
The mitigation works by ensuring all RET instructions speculate to
a controlled location, similar to how speculation is controlled in the
retpoline sequence. To accomplish this, the __x86_return_thunk forces
the CPU to mispredict every function return using a 'safe return'
sequence.
To ensure the safety of this mitigation, the kernel must ensure that the
safe return sequence is itself free from attacker interference. In Zen3
and Zen4, this is accomplished by creating a BTB alias between the
untraining function srso_untrain_ret_alias() and the safe return
function srso_safe_ret_alias() which results in evicting a potentially
poisoned BTB entry and using that safe one for all function returns.
In older Zen1 and Zen2, this is accomplished using a reinterpretation
technique similar to Retbleed one: srso_untrain_ret() and
srso_safe_ret().
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Unlike Intel's Enhanced IBRS feature, AMD's Automatic IBRS does not
provide protection to processes running at CPL3/user mode, see section
"Extended Feature Enable Register (EFER)" in the APM v2 at
https://bugzilla.kernel.org/attachment.cgi?id=304652
Explicitly enable STIBP to protect against cross-thread CPL3
branch target injections on systems with Automatic IBRS enabled.
Also update the relevant documentation.
Fixes: e7862eda30 ("x86/cpu: Support AMD Automatic IBRS")
Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230720194727.67022-1-kim.phillips@amd.com
The Gather Data Sampling (GDS) vulnerability allows malicious software
to infer stale data previously stored in vector registers. This may
include sensitive data such as cryptographic keys. GDS is mitigated in
microcode, and systems with up-to-date microcode are protected by
default. However, any affected system that is running with older
microcode will still be vulnerable to GDS attacks.
Since the gather instructions used by the attacker are part of the
AVX2 and AVX512 extensions, disabling these extensions prevents gather
instructions from being executed, thereby mitigating the system from
GDS. Disabling AVX2 is sufficient, but we don't have the granularity
to do this. The XCR0[2] disables AVX, with no option to just disable
AVX2.
Add a kernel parameter gather_data_sampling=force that will enable the
microcode mitigation if available, otherwise it will disable AVX on
affected systems.
This option will be ignored if cmdline mitigations=off.
This is a *big* hammer. It is known to break buggy userspace that
uses incomplete, buggy AVX enumeration. Unfortunately, such userspace
does exist in the wild:
https://www.mail-archive.com/bug-coreutils@gnu.org/msg33046.html
[ dhansen: add some more ominous warnings about disabling AVX ]
Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Gather Data Sampling (GDS) is a hardware vulnerability which allows
unprivileged speculative access to data which was previously stored in
vector registers.
Intel processors that support AVX2 and AVX512 have gather instructions
that fetch non-contiguous data elements from memory. On vulnerable
hardware, when a gather instruction is transiently executed and
encounters a fault, stale data from architectural or internal vector
registers may get transiently stored to the destination vector
register allowing an attacker to infer the stale data using typical
side channel techniques like cache timing attacks.
This mitigation is different from many earlier ones for two reasons.
First, it is enabled by default and a bit must be set to *DISABLE* it.
This is the opposite of normal mitigation polarity. This means GDS can
be mitigated simply by updating microcode and leaving the new control
bit alone.
Second, GDS has a "lock" bit. This lock bit is there because the
mitigation affects the hardware security features KeyLocker and SGX.
It needs to be enabled and *STAY* enabled for these features to be
mitigated against GDS.
The mitigation is enabled in the microcode by default. Disable it by
setting gather_data_sampling=off or by disabling all mitigations with
mitigations=off. The mitigation status can be checked by reading:
/sys/devices/system/cpu/vulnerabilities/gather_data_sampling
Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Move the x86 documentation under Documentation/arch/ as a way of cleaning
up the top-level directory and making the structure of our docs more
closely match the structure of the source directories it describes.
All in-kernel references to the old paths have been updated.
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/20230315211523.108836-1-corbet@lwn.net/
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
- Return -EIO instead of success when the certificate buffer for SEV
guests is not large enough.
- Allow STIPB to be enabled with legacy IBSR. Legacy IBRS is cleared on
return to userspace for performance reasons, but the leaves user space
vulnerable to cross-thread attacks which STIBP prevents. Update the
documentation accordingly.
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Merge tag 'x86-urgent-2023-03-05' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 updates from Thomas Gleixner:
"A small set of updates for x86:
- Return -EIO instead of success when the certificate buffer for SEV
guests is not large enough
- Allow STIPB to be enabled with legacy IBSR. Legacy IBRS is cleared
on return to userspace for performance reasons, but the leaves user
space vulnerable to cross-thread attacks which STIBP prevents.
Update the documentation accordingly"
* tag 'x86-urgent-2023-03-05' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
virt/sev-guest: Return -EIO if certificate buffer is not large enough
Documentation/hw-vuln: Document the interaction between IBRS and STIBP
x86/speculation: Allow enabling STIBP with legacy IBRS
Explain why STIBP is needed with legacy IBRS as currently implemented
(KERNEL_IBRS) and why STIBP is not needed when enhanced IBRS is enabled.
Fixes: 7c693f54c8 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS")
Signed-off-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230227060541.1939092-2-kpsingh@kernel.org
changes include:
- Some significant additions to the memory-management documentation
- Some improvements to navigation in the HTML-rendered docs
- More Spanish and Chinese translations
...and the usual set of typo fixes and such.
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Merge tag 'docs-6.3' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"It has been a moderately calm cycle for documentation; the significant
changes include:
- Some significant additions to the memory-management documentation
- Some improvements to navigation in the HTML-rendered docs
- More Spanish and Chinese translations
... and the usual set of typo fixes and such"
* tag 'docs-6.3' of git://git.lwn.net/linux: (68 commits)
Documentation/watchdog/hpwdt: Fix Format
Documentation/watchdog/hpwdt: Fix Reference
Documentation: core-api: padata: correct spelling
docs/mm: Physical Memory: correct spelling in reference to CONFIG_PAGE_EXTENSION
docs: Use HTML comments for the kernel-toc SPDX line
docs: Add more information to the HTML sidebar
Documentation: KVM: Update AMD memory encryption link
printk: Document that CONFIG_BOOT_PRINTK_DELAY required for boot_delay=
Documentation: userspace-api: correct spelling
Documentation: sparc: correct spelling
Documentation: driver-api: correct spelling
Documentation: admin-guide: correct spelling
docs: add workload-tracing document to admin-guide
docs/admin-guide/mm: remove useless markup
docs/mm: remove useless markup
docs/mm: Physical Memory: remove useless markup
docs/sp_SP: Add process magic-number translation
docs: ftrace: always use canonical ftrace path
Doc/damon: fix the data path error
dma-buf: Add "dma-buf" to title of documentation
...
where possible, when supporting a debug registers swap feature for
SEV-ES guests
- Add support for AMD's version of eIBRS called Automatic IBRS which is
a set-and-forget control of indirect branch restriction speculation
resources on privilege change
- Add support for a new x86 instruction - LKGS - Load kernel GS which is
part of the FRED infrastructure
- Reset SPEC_CTRL upon init to accomodate use cases like kexec which
rediscover
- Other smaller fixes and cleanups
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Merge tag 'x86_cpu_for_v6.3_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 cpuid updates from Borislav Petkov:
- Cache the AMD debug registers in per-CPU variables to avoid MSR
writes where possible, when supporting a debug registers swap feature
for SEV-ES guests
- Add support for AMD's version of eIBRS called Automatic IBRS which is
a set-and-forget control of indirect branch restriction speculation
resources on privilege change
- Add support for a new x86 instruction - LKGS - Load kernel GS which
is part of the FRED infrastructure
- Reset SPEC_CTRL upon init to accomodate use cases like kexec which
rediscover
- Other smaller fixes and cleanups
* tag 'x86_cpu_for_v6.3_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/amd: Cache debug register values in percpu variables
KVM: x86: Propagate the AMD Automatic IBRS feature to the guest
x86/cpu: Support AMD Automatic IBRS
x86/cpu, kvm: Add the SMM_CTL MSR not present feature
x86/cpu, kvm: Add the Null Selector Clears Base feature
x86/cpu, kvm: Move X86_FEATURE_LFENCE_RDTSC to its native leaf
x86/cpu, kvm: Add the NO_NESTED_DATA_BP feature
KVM: x86: Move open-coded CPUID leaf 0x80000021 EAX bit propagation code
x86/cpu, kvm: Add support for CPUID_80000021_EAX
x86/gsseg: Add the new <asm/gsseg.h> header to <asm/asm-prototypes.h>
x86/gsseg: Use the LKGS instruction if available for load_gs_index()
x86/gsseg: Move load_gs_index() to its own new header file
x86/gsseg: Make asm_load_gs_index() take an u16
x86/opcode: Add the LKGS instruction to x86-opcode-map
x86/cpufeature: Add the CPU feature bit for LKGS
x86/bugs: Reset speculation control settings on init
x86/cpu: Remove redundant extern x86_read_arch_cap_msr()
The following warning:
Documentation/admin-guide/hw-vuln/cross-thread-rsb.rst:92: ERROR: Unexpected indentation.
was introduced by commit 493a2c2d23. Fix it by placing everything in
the same paragraph and also use a monospace font.
Fixes: 493a2c2d23 ("Documentation/hw-vuln: Add documentation for Cross-Thread Return Predictions")
Reported-by: Stephen Rothwell <sfr@canb@auug.org.au>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add the admin guide for the Cross-Thread Return Predictions vulnerability.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <60f9c0b4396956ce70499ae180cb548720b25c7e.1675956146.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The AMD Zen4 core supports a new feature called Automatic IBRS.
It is a "set-and-forget" feature that means that, like Intel's Enhanced IBRS,
h/w manages its IBRS mitigation resources automatically across CPL transitions.
The feature is advertised by CPUID_Fn80000021_EAX bit 8 and is enabled by
setting MSR C000_0080 (EFER) bit 21.
Enable Automatic IBRS by default if the CPU feature is present. It typically
provides greater performance over the incumbent generic retpolines mitigation.
Reuse the SPECTRE_V2_EIBRS spectre_v2_mitigation enum. AMD Automatic IBRS and
Intel Enhanced IBRS have similar enablement. Add NO_EIBRS_PBRSB to
cpu_vuln_whitelist, since AMD Automatic IBRS isn't affected by PBRSB-eIBRS.
The kernel command line option spectre_v2=eibrs is used to select AMD Automatic
IBRS, if available.
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Sean Christopherson <seanjc@google.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20230124163319.2277355-8-kim.phillips@amd.com
but a few significant changes even so:
- A complete rewriting of the top-level index.rst file, which mostly
reflects itself in a redone top page in the HTML-rendered docs. The hope
is that the new organization will be a friendlier starting point for
both users and developers.
- Some math-rendering improvements.
- A coding-style.rst update on the use of BUG() and WARN()
- A big maintainer-PHP guide update.
- Some code-of-conduct updates
- More Chinese translation work
Plus the usual pile of typo fixes, corrections, and updates.
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Merge tag 'docs-6.1' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"There's not a huge amount of activity in the docs tree this time
around, but a few significant changes even so:
- A complete rewriting of the top-level index.rst file, which mostly
reflects itself in a redone top page in the HTML-rendered docs. The
hope is that the new organization will be a friendlier starting
point for both users and developers.
- Some math-rendering improvements.
- A coding-style.rst update on the use of BUG() and WARN()
- A big maintainer-PHP guide update.
- Some code-of-conduct updates
- More Chinese translation work
Plus the usual pile of typo fixes, corrections, and updates"
* tag 'docs-6.1' of git://git.lwn.net/linux: (66 commits)
checkpatch: warn on usage of VM_BUG_ON() and other BUG variants
coding-style.rst: document BUG() and WARN() rules ("do not crash the kernel")
Documentation: devres: add missing IO helper
Documentation: devres: update IRQ helper
Documentation/mm: modify page_referenced to folio_referenced
Documentation/CoC: Reflect current CoC interpretation and practices
docs/doc-guide: Add documentation on SPHINX_IMGMATH
docs: process/5.Posting.rst: clarify use of Reported-by: tag
docs, kprobes: Fix the wrong location of Kprobes
docs: add a man-pages link to the front page
docs: put atomic*.txt and memory-barriers.txt into the core-api book
docs: move asm-annotations.rst into core-api
docs: remove some index.rst cruft
docs: reconfigure the HTML left column
docs: Rewrite the front page
docs: promote the title of process/index.rst
Documentation: devres: add missing SPI helper
Documentation: devres: add missing PINCTRL helpers
docs: hugetlbpage.rst: fix a typo of hugepage size
docs/zh_CN: Add new translation of admin-guide/bootconfig.rst
...
commit 7c693f54c8 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS")
adds the "ibrs " option in
Documentation/admin-guide/kernel-parameters.txt but omits it to
Documentation/admin-guide/hw-vuln/spectre.rst, add it.
Signed-off-by: Lin Yujun <linyujun809@huawei.com>
Link: https://lore.kernel.org/r/20220830123614.23007-1-linyujun809@huawei.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Older Intel CPUs that are not in the affected processor list for MMIO
Stale Data vulnerabilities currently report "Not affected" in sysfs,
which may not be correct. Vulnerability status for these older CPUs is
unknown.
Add known-not-affected CPUs to the whitelist. Report "unknown"
mitigation status for CPUs that are not in blacklist, whitelist and also
don't enumerate MSR ARCH_CAPABILITIES bits that reflect hardware
immunity to MMIO Stale Data vulnerabilities.
Mitigation is not deployed when the status is unknown.
[ bp: Massage, fixup. ]
Fixes: 8d50cdf8b8 ("x86/speculation/mmio: Add sysfs reporting for Processor MMIO Stale Data")
Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Suggested-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/a932c154772f2121794a5f2eded1a11013114711.1657846269.git.pawan.kumar.gupta@linux.intel.com
tl;dr: The Enhanced IBRS mitigation for Spectre v2 does not work as
documented for RET instructions after VM exits. Mitigate it with a new
one-entry RSB stuffing mechanism and a new LFENCE.
== Background ==
Indirect Branch Restricted Speculation (IBRS) was designed to help
mitigate Branch Target Injection and Speculative Store Bypass, i.e.
Spectre, attacks. IBRS prevents software run in less privileged modes
from affecting branch prediction in more privileged modes. IBRS requires
the MSR to be written on every privilege level change.
To overcome some of the performance issues of IBRS, Enhanced IBRS was
introduced. eIBRS is an "always on" IBRS, in other words, just turn
it on once instead of writing the MSR on every privilege level change.
When eIBRS is enabled, more privileged modes should be protected from
less privileged modes, including protecting VMMs from guests.
== Problem ==
Here's a simplification of how guests are run on Linux' KVM:
void run_kvm_guest(void)
{
// Prepare to run guest
VMRESUME();
// Clean up after guest runs
}
The execution flow for that would look something like this to the
processor:
1. Host-side: call run_kvm_guest()
2. Host-side: VMRESUME
3. Guest runs, does "CALL guest_function"
4. VM exit, host runs again
5. Host might make some "cleanup" function calls
6. Host-side: RET from run_kvm_guest()
Now, when back on the host, there are a couple of possible scenarios of
post-guest activity the host needs to do before executing host code:
* on pre-eIBRS hardware (legacy IBRS, or nothing at all), the RSB is not
touched and Linux has to do a 32-entry stuffing.
* on eIBRS hardware, VM exit with IBRS enabled, or restoring the host
IBRS=1 shortly after VM exit, has a documented side effect of flushing
the RSB except in this PBRSB situation where the software needs to stuff
the last RSB entry "by hand".
IOW, with eIBRS supported, host RET instructions should no longer be
influenced by guest behavior after the host retires a single CALL
instruction.
However, if the RET instructions are "unbalanced" with CALLs after a VM
exit as is the RET in #6, it might speculatively use the address for the
instruction after the CALL in #3 as an RSB prediction. This is a problem
since the (untrusted) guest controls this address.
Balanced CALL/RET instruction pairs such as in step #5 are not affected.
== Solution ==
The PBRSB issue affects a wide variety of Intel processors which
support eIBRS. But not all of them need mitigation. Today,
X86_FEATURE_RSB_VMEXIT triggers an RSB filling sequence that mitigates
PBRSB. Systems setting RSB_VMEXIT need no further mitigation - i.e.,
eIBRS systems which enable legacy IBRS explicitly.
However, such systems (X86_FEATURE_IBRS_ENHANCED) do not set RSB_VMEXIT
and most of them need a new mitigation.
Therefore, introduce a new feature flag X86_FEATURE_RSB_VMEXIT_LITE
which triggers a lighter-weight PBRSB mitigation versus RSB_VMEXIT.
The lighter-weight mitigation performs a CALL instruction which is
immediately followed by a speculative execution barrier (INT3). This
steers speculative execution to the barrier -- just like a retpoline
-- which ensures that speculation can never reach an unbalanced RET.
Then, ensure this CALL is retired before continuing execution with an
LFENCE.
In other words, the window of exposure is opened at VM exit where RET
behavior is troublesome. While the window is open, force RSB predictions
sampling for RET targets to a dead end at the INT3. Close the window
with the LFENCE.
There is a subset of eIBRS systems which are not vulnerable to PBRSB.
Add these systems to the cpu_vuln_whitelist[] as NO_EIBRS_PBRSB.
Future systems that aren't vulnerable will set ARCH_CAP_PBRSB_NO.
[ bp: Massage, incorporate review comments from Andy Cooper. ]
Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Co-developed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Add the admin guide for Processor MMIO stale data vulnerabilities.
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Update the link to the "Software Techniques for Managing Speculation
on AMD Processors" whitepaper.
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Update the doc with the new fun.
[ bp: Massage commit message. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
The config RANDOMIZE_SLAB does not exist, the authors probably intended to
refer to the config RANDOMIZE_BASE, which provides kernel address-space
randomization. They probably just confused SLAB with BASE (these two
four-letter words coincidentally share three common letters), as they also
point out the config SLAB_FREELIST_RANDOM as further randomization within
the same sentence.
Fix the reference of the config for kernel address-space randomization to
the config that provides that.
Fixes: 6e88559470 ("Documentation: Add section about CPU vulnerabilities for Spectre")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20211230171940.27558-1-lukas.bulwahn@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Merge tag 'kernel.sys.v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux
Pull prctl updates from Christian Brauner:
"This contains the missing prctl uapi pieces for PR_SCHED_CORE.
In order to activate core scheduling the caller is expected to specify
the scope of the new core scheduling domain.
For example, passing 2 in the 4th argument of
prctl(PR_SCHED_CORE, PR_SCHED_CORE_CREATE, <pid>, 2, 0);
would indicate that the new core scheduling domain encompasses all
tasks in the process group of <pid>. Specifying 0 would only create a
core scheduling domain for the thread identified by <pid> and 2 would
encompass the whole thread-group of <pid>.
Note, the values 0, 1, and 2 correspond to PIDTYPE_PID, PIDTYPE_TGID,
and PIDTYPE_PGID. A first version tried to expose those values
directly to which I objected because:
- PIDTYPE_* is an enum that is kernel internal which we should not
expose to userspace directly.
- PIDTYPE_* indicates what a given struct pid is used for it doesn't
express a scope.
But what the 4th argument of PR_SCHED_CORE prctl() expresses is the
scope of the operation, i.e. the scope of the core scheduling domain
at creation time. So Eugene's patch now simply introduces three new
defines PR_SCHED_CORE_SCOPE_THREAD, PR_SCHED_CORE_SCOPE_THREAD_GROUP,
and PR_SCHED_CORE_SCOPE_PROCESS_GROUP. They simply express what
happens.
This has been on the mailing list for quite a while with all relevant
scheduler folks Cced. I announced multiple times that I'd pick this up
if I don't see or her anyone else doing it. None of this touches
proper scheduler code but only concerns uapi so I think this is fine.
With core scheduling being quite common now for vm managers (e.g.
moving individual vcpu threads into their own core scheduling domain)
and container managers (e.g. moving the init process into its own core
scheduling domain and letting all created children inherit it) having
to rely on raw numbers passed as the 4th argument in prctl() is a bit
annoying and everyone is starting to come up with their own defines"
* tag 'kernel.sys.v5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
uapi/linux/prctl: provide macro definitions for the PR_SCHED_CORE type argument
This would need updating to make prctl be the new default, but it's
simpler to delete it and refer to the dup.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201105001406.13005-2-aarcange@redhat.com
Switch the kernel default of SSBD and STIBP to the ones with
CONFIG_SECCOMP=n (i.e. spec_store_bypass_disable=prctl
spectre_v2_user=prctl) even if CONFIG_SECCOMP=y.
Several motivations listed below:
- If SMT is enabled the seccomp jail can still attack the rest of the
system even with spectre_v2_user=seccomp by using MDS-HT (except on
XEON PHI where MDS can be tamed with SMT left enabled, but that's a
special case). Setting STIBP become a very expensive window dressing
after MDS-HT was discovered.
- The seccomp jail cannot attack the kernel with spectre-v2-HT
regardless (even if STIBP is not set), but with MDS-HT the seccomp
jail can attack the kernel too.
- With spec_store_bypass_disable=prctl the seccomp jail can attack the
other userland (guest or host mode) using spectre-v2-HT, but the
userland attack is already mitigated by both ASLR and pid namespaces
for host userland and through virt isolation with libkrun or
kata. (if something if somebody is worried about spectre-v2-HT it's
best to mount proc with hidepid=2,gid=proc on workstations where not
all apps may run under container runtimes, rather than slowing down
all seccomp jails, but the best is to add pid namespaces to the
seccomp jail). As opposed MDS-HT is not mitigated and the seccomp
jail can still attack all other host and guest userland if SMT is
enabled even with spec_store_bypass_disable=seccomp.
- If full security is required then MDS-HT must also be mitigated with
nosmt and then spectre_v2_user=prctl and spectre_v2_user=seccomp
would become identical.
- Setting spectre_v2_user=seccomp is overall lower priority than to
setting javascript.options.wasm false in about:config to protect
against remote wasm MDS-HT, instead of worrying about Spectre-v2-HT
and STIBP which again is already statistically well mitigated by
other means in userland and it's fully mitigated in kernel with
retpolines (unlike the wasm assist call with MDS-HT).
- SSBD is needed to prevent reading the JIT memory and the primary
user being the OpenJDK. However the primary user of SSBD wouldn't be
covered by spec_store_bypass_disable=seccomp because it doesn't use
seccomp and the primary user also explicitly declined to set
PR_SET_SPECULATION_CTRL+PR_SPEC_STORE_BYPASS despite it easily
could. In fact it would need to set it only when the sandboxing
mechanism is enabled for javaws applets, but it still declined it by
declaring security within the same user address space as an
untenable objective for their JIT, even in the sandboxing case where
performance would be a lesser concern (for the record: I kind of
disagree in not setting PR_SPEC_STORE_BYPASS in the sandbox case and
I prefer to run javaws through a wrapper that sets
PR_SPEC_STORE_BYPASS if I need). In turn it can be inferred that
even if the primary user of SSBD would use seccomp, they would
invoke it with SECCOMP_FILTER_FLAG_SPEC_ALLOW by now.
- runc/crun already set SECCOMP_FILTER_FLAG_SPEC_ALLOW by default, k8s
and podman have a default json seccomp allowlist that cannot be
slowed down, so for the #1 seccomp user this change is already a
noop.
- systemd/sshd or other apps that use seccomp, if they really need
STIBP or SSBD, they need to explicitly set the
PR_SET_SPECULATION_CTRL by now. The stibp/ssbd seccomp blind
catch-all approach was done probably initially with a wishful
thinking objective to pretend to have a peace of mind that it could
magically fix it all. That was wishful thinking before MDS-HT was
discovered, but after MDS-HT has been discovered it become just
window dressing.
- For qemu "-sandbox" seccomp jail it wouldn't make sense to set STIBP
or SSBD. SSBD doesn't help with KVM because there's no JIT (if it's
needed with TCG it should be an opt-in with
PR_SET_SPECULATION_CTRL+PR_SPEC_STORE_BYPASS and it shouldn't
slowdown KVM for nothing). For qemu+KVM STIBP would be even more
window dressing than it is for all other apps, because in the
qemu+KVM case there's not only the MDS attack to worry about with
SMT enabled. Even after disabling SMT, there's still a theoretical
spectre-v2 attack possible within the same thread context from guest
mode to host ring3 that the host kernel retpoline mitigation has no
theoretical chance to mitigate. On some kernels a
ibrs-always/ibrs-retpoline opt-in model is provided that will
enabled IBRS in the qemu host ring3 userland which fixes this
theoretical concern. Only after enabling IBRS in the host userland
it would then make sense to proceed and worry about STIBP and an
attack on the other host userland, but then again SMT would need to
be disabled for full security anyway, so that would render STIBP
again a noop.
- last but not the least: the lack of "spec_store_bypass_disable=prctl
spectre_v2_user=prctl" means the moment a guest boots and
sshd/systemd runs, the guest kernel will write to SPEC_CTRL MSR
which will make the guest vmexit forever slower, forcing KVM to
issue a very slow rdmsr instruction at every vmexit. So the end
result is that SPEC_CTRL MSR is only available in GCE. Most other
public cloud providers don't expose SPEC_CTRL, which means that not
only STIBP/SSBD isn't available, but IBPB isn't available either
(which would cause no overhead to the guest or the hypervisor
because it's write only and requires no reading during vmexit). So
the current default already net loss in security (missing IBPB)
which means most public cloud providers cannot achieve a fully
secure guest with nosmt (and nosmt is enough to fully mitigate
MDS-HT). It also means GCE and is unfairly penalized in performance
because it provides the option to enable full security in the guest
as an opt-in (i.e. nosmt and IBPB). So this change will allow all
cloud providers to expose SPEC_CTRL without incurring into any
hypervisor slowdown and at the same time it will remove the unfair
penalization of GCE performance for doing the right thing and it'll
allow to get full security with nosmt with IBPB being available (and
STIBP becoming meaningless).
Example to put things in prospective: the STIBP enabled in seccomp has
never been about protecting apps using seccomp like sshd from an
attack from a malicious userland, but to the contrary it has always
been about protecting the system from an attack from sshd, after a
successful remote network exploit against sshd. In fact initially it
wasn't obvious STIBP would work both ways (STIBP was about preventing
the task that runs with STIBP to be attacked with spectre-v2-HT, but
accidentally in the STIBP case it also prevents the attack in the
other direction). In the hypothetical case that sshd has been remotely
exploited the last concern should be STIBP being set, because it'll be
still possible to obtain info even from the kernel by using MDS if
nosmt wasn't set (and if it was set, STIBP is a noop in the first
place). As opposed kernel cannot leak anything with spectre-v2 HT
because of retpolines and the userland is mitigated by ASLR already
and ideally PID namespaces too. If something it'd be worth checking if
sshd run the seccomp thread under pid namespaces too if available in
the running kernel. SSBD also would be a noop for sshd, since sshd
uses no JIT. If sshd prefers to keep doing the STIBP window dressing
exercise, it still can even after this change of defaults by opting-in
with PR_SPEC_INDIRECT_BRANCH.
Ultimately setting SSBD and STIBP by default for all seccomp jails is
a bad sweet spot and bad default with more cons than pros that end up
reducing security in the public cloud (by giving an huge incentive to
not expose SPEC_CTRL which would be needed to get full security with
IBPB after setting nosmt in the guest) and by excessively hurting
performance to more secure apps using seccomp that end up having to
opt out with SECCOMP_FILTER_FLAG_SPEC_ALLOW.
The following is the verified result of the new default with SMT
enabled:
(gdb) print spectre_v2_user_stibp
$1 = SPECTRE_V2_USER_PRCTL
(gdb) print spectre_v2_user_ibpb
$2 = SPECTRE_V2_USER_PRCTL
(gdb) print ssb_mode
$3 = SPEC_STORE_BYPASS_PRCTL
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201104235054.5678-1-aarcange@redhat.com
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/lkml/AAA2EF2C-293D-4D5B-BFA6-FF655105CD84@redhat.com
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/lkml/c0722838-06f7-da6b-138f-e0f26362f16a@redhat.com
Commit 7ac592aa35 ("sched: prctl() core-scheduling interface")
made use of enum pid_type in prctl's arg4; this type and the associated
enumeration definitions are not exposed to userspace. Christian
has suggested to provide additional macro definitions that convey
the meaning of the type argument more in alignment with its actual
usage, and this patch does exactly that.
Link: https://lore.kernel.org/r/20210825170613.GA3884@asgard.redhat.com
Suggested-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Complements: 7ac592aa35 ("sched: prctl() core-scheduling interface")
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
- A reworking of PDF generation to yield better results for documents
using CJK fonts in particular.
- A new set of translations into traditional Chinese, a dialect for which
I am assured there is a community of interested readers.
- A lot more regular Chinese translation work as well.
...plus the usual assortment of updates, fixes, typo tweaks, etc.
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Merge tag 'docs-5.15' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"Yet another set of documentation changes:
- A reworking of PDF generation to yield better results for documents
using CJK fonts in particular.
- A new set of translations into traditional Chinese, a dialect for
which I am assured there is a community of interested readers.
- A lot more regular Chinese translation work as well.
... plus the usual assortment of updates, fixes, typo tweaks, etc"
* tag 'docs-5.15' of git://git.lwn.net/linux: (55 commits)
docs: sphinx-requirements: Move sphinx_rtd_theme to top
docs: pdfdocs: Enable language-specific font choice of zh_TW translations
docs: pdfdocs: Teach xeCJK about character classes of quotation marks
docs: pdfdocs: Permit AutoFakeSlant for CJK fonts
docs: pdfdocs: One-half spacing for CJK translations
docs: pdfdocs: Add conf.py local to translations for ascii-art alignment
docs: pdfdocs: Preserve inter-phrase space in Korean translations
docs: pdfdocs: Choose Serif font as CJK mainfont if possible
docs: pdfdocs: Add CJK-language-specific font settings
docs: pdfdocs: Refactor config for CJK document
scripts/kernel-doc: Override -Werror from KCFLAGS with KDOC_WERROR
docs/zh_CN: Add zh_CN/accounting/psi.rst
doc: align Italian translation
Documentation/features/vm: riscv supports THP now
docs/zh_CN: add infiniband user_verbs translation
docs/zh_CN: add infiniband user_mad translation
docs/zh_CN: add infiniband tag_matching translation
docs/zh_CN: add infiniband sysfs translation
docs/zh_CN: add infiniband opa_vnic translation
docs/zh_CN: add infiniband ipoib translation
...
Add documentation of l1d flushing, explain the need for the
feature and how it can be used.
Signed-off-by: Balbir Singh <sblbir@amazon.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210108121056.21940-6-sblbir@amazon.com
Rephrase the "For MDS" section in core-scheduling.rst for the purpose of
making it clearer what is meant by "kernel memory is still considered
untrusted".
Suggested-by: Vineeth Pillai <Vineeth.Pillai@microsoft.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: Joel Fernandes (Google) <joelaf@google.com>
Link: https://lore.kernel.org/r/20210721190250.26095-1-fmdefrancesco@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
- Some kernel-doc cleanups. That script is still regex onslaught from
hell, but it has gotten a little better.
- Improvements to the checkpatch docs, which are also used by the tool
itself.
- A major update to the pathname lookup documentation.
- Elimination of :doc: markup, since our automarkup magic can create
references from filenames without all the extra noise.
- The flurry of Chinese translation activity continues.
Plus, of course, the usual collection of updates, typo fixes, and warning
fixes.
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Merge tag 'docs-5.14' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"This was a reasonably active cycle for documentation; this includes:
- Some kernel-doc cleanups. That script is still regex onslaught from
hell, but it has gotten a little better.
- Improvements to the checkpatch docs, which are also used by the
tool itself.
- A major update to the pathname lookup documentation.
- Elimination of :doc: markup, since our automarkup magic can create
references from filenames without all the extra noise.
- The flurry of Chinese translation activity continues.
Plus, of course, the usual collection of updates, typo fixes, and
warning fixes"
* tag 'docs-5.14' of git://git.lwn.net/linux: (115 commits)
docs: path-lookup: use bare function() rather than literals
docs: path-lookup: update symlink description
docs: path-lookup: update get_link() ->follow_link description
docs: path-lookup: update WALK_GET, WALK_PUT desc
docs: path-lookup: no get_link()
docs: path-lookup: update i_op->put_link and cookie description
docs: path-lookup: i_op->follow_link replaced with i_op->get_link
docs: path-lookup: Add macro name to symlink limit description
docs: path-lookup: remove filename_mountpoint
docs: path-lookup: update do_last() part
docs: path-lookup: update path_mountpoint() part
docs: path-lookup: update path_to_nameidata() part
docs: path-lookup: update follow_managed() part
docs: Makefile: Use CONFIG_SHELL not SHELL
docs: Take a little noise out of the build process
docs: x86: avoid using ReST :doc:`foo` markup
docs: virt: kvm: s390-pv-boot.rst: avoid using ReST :doc:`foo` markup
docs: userspace-api: landlock.rst: avoid using ReST :doc:`foo` markup
docs: trace: ftrace.rst: avoid using ReST :doc:`foo` markup
docs: trace: coresight: coresight.rst: avoid using ReST :doc:`foo` markup
...
Now that core scheduling is merged, update the documentation.
Co-developed-by: Chris Hyser <chris.hyser@oracle.com>
Signed-off-by: Chris Hyser <chris.hyser@oracle.com>
Co-developed-by: Josh Don <joshdon@google.com>
Signed-off-by: Josh Don <joshdon@google.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210603013136.370918-1-joel@joelfernandes.org
On systems that have virtualization disabled or unsupported, sysfs
mitigation for X86_BUG_ITLB_MULTIHIT is reported incorrectly as:
$ cat /sys/devices/system/cpu/vulnerabilities/itlb_multihit
KVM: Vulnerable
System is not vulnerable to DoS attack from a rogue guest when
virtualization is disabled or unsupported in the hardware. Change the
mitigation reporting for these cases.
Fixes: b8e8c8303f ("kvm: mmu: ITLB_MULTIHIT mitigation")
Reported-by: Nelson Dsouza <nelson.dsouza@linux.intel.com>
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/0ba029932a816179b9d14a30db38f0f11ef1f166.1594925782.git.pawan.kumar.gupta@linux.intel.com
The lengths of underlines must match the titles to avoid build warnings.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Mark Gross<mgross@linux.intel.com>
Link: https://lore.kernel.org/r/20200615203645.11545-1-xypron.glpk@gmx.de
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Pull x86 srbds fixes from Thomas Gleixner:
"The 9th episode of the dime novel "The performance killer" with the
subtitle "Slow Randomizing Boosts Denial of Service".
SRBDS is an MDS-like speculative side channel that can leak bits from
the random number generator (RNG) across cores and threads. New
microcode serializes the processor access during the execution of
RDRAND and RDSEED. This ensures that the shared buffer is overwritten
before it is released for reuse. This is equivalent to a full bus
lock, which means that many threads running the RNG instructions in
parallel have the same effect as the same amount of threads issuing a
locked instruction targeting an address which requires locking of two
cachelines at once.
The mitigation support comes with the usual pile of unpleasant
ingredients:
- command line options
- sysfs file
- microcode checks
- a list of vulnerable CPUs identified by model and stepping this
time which requires stepping match support for the cpu match logic.
- the inevitable slowdown of affected CPUs"
* branch 'x86/srbds' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/speculation: Add Ivy Bridge to affected list
x86/speculation: Add SRBDS vulnerability and mitigation documentation
x86/speculation: Add Special Register Buffer Data Sampling (SRBDS) mitigation
x86/cpu: Add 'table' argument to cpu_matches()
There are 4 IRQ documentation files under Documentation/*.txt.
Move them into a new directory (core-api/irq) and add a new
index file for it.
While here, use a title markup for the Debugging section of the
irq-domain.rst file.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/2da7485c3718e1442e6b4c2dd66857b776e8899b.1588345503.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Linus Torvalds