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Josh Poimboeuf 83e6e48e70 x86/speculation: Prepare entry code for Spectre v1 swapgs mitigations 
commit 18ec54fdd6 upstream

Spectre v1 isn't only about array bounds checks.  It can affect any
conditional checks.  The kernel entry code interrupt, exception, and NMI
handlers all have conditional swapgs checks.  Those may be problematic in
the context of Spectre v1, as kernel code can speculatively run with a user
GS.

For example:

	if (coming from user space)
		swapgs
	mov %gs:<percpu_offset>, %reg
	mov (%reg), %reg1

When coming from user space, the CPU can speculatively skip the swapgs, and
then do a speculative percpu load using the user GS value.  So the user can
speculatively force a read of any kernel value.  If a gadget exists which
uses the percpu value as an address in another load/store, then the
contents of the kernel value may become visible via an L1 side channel
attack.

A similar attack exists when coming from kernel space.  The CPU can
speculatively do the swapgs, causing the user GS to get used for the rest
of the speculative window.

The mitigation is similar to a traditional Spectre v1 mitigation, except:

  a) index masking isn't possible; because the index (percpu offset)
     isn't user-controlled; and

  b) an lfence is needed in both the "from user" swapgs path and the
     "from kernel" non-swapgs path (because of the two attacks described
     above).

The user entry swapgs paths already have SWITCH_TO_KERNEL_CR3, which has a
CR3 write when PTI is enabled.  Since CR3 writes are serializing, the
lfences can be skipped in those cases.

On the other hand, the kernel entry swapgs paths don't depend on PTI.

To avoid unnecessary lfences for the user entry case, create two separate
features for alternative patching:

  X86_FEATURE_FENCE_SWAPGS_USER
  X86_FEATURE_FENCE_SWAPGS_KERNEL

Use these features in entry code to patch in lfences where needed.

The features aren't enabled yet, so there's no functional change.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-08-06 19:05:29 +02:00
arch x86/speculation: Prepare entry code for Spectre v1 swapgs mitigations 2019-08-06 19:05:29 +02:00
block block/bio-integrity: fix a memory leak bug 2019-07-31 07:28:55 +02:00
certs Replace magic for trusting the secondary keyring with #define 2018-09-09 19:55:54 +02:00
crypto crypto: chacha20poly1305 - fix atomic sleep when using async algorithm 2019-07-31 07:28:35 +02:00
Documentation arm64: dts: marvell: Fix A37xx UART0 register size 2019-08-04 09:32:00 +02:00
drivers eeprom: at24: make spd world-readable again 2019-08-06 19:05:28 +02:00
firmware License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs Btrfs: fix race leading to fs corruption after transaction abort 2019-08-06 19:05:25 +02:00
include uapi linux/coda_psdev.h: move upc_req definition from uapi to kernel side headers 2019-08-06 19:05:24 +02:00
init init: initialize jump labels before command line option parsing 2019-05-16 19:42:23 +02:00
ipc ipc/mqueue.c: only perform resource calculation if user valid 2019-08-06 19:05:24 +02:00
kernel kernel/module.c: Only return -EEXIST for modules that have finished loading 2019-08-06 19:05:20 +02:00
lib lib/strscpy: Shut up KASAN false-positives in strscpy() 2019-07-31 07:28:44 +02:00
mm mm/cma.c: fail if fixed declaration can't be honored 2019-08-06 19:05:23 +02:00
net ip_tunnel: allow not to count pkts on tstats by setting skb's dev to NULL 2019-08-04 09:32:03 +02:00
samples samples, bpf: fix to change the buffer size for read() 2019-07-21 09:04:17 +02:00
scripts kallsyms: exclude kasan local symbols on s390 2019-07-31 07:28:54 +02:00
security selinux: fix memory leak in policydb_init() 2019-08-06 19:05:26 +02:00
sound ALSA: hda - Add a conexant codec entry to let mute led work 2019-07-31 07:28:58 +02:00
tools objtool: Support GCC 9 cold subfunction naming scheme 2019-08-06 19:05:28 +02:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: arm/arm64: vgic: Fix kvm_device leak in vgic_its_destroy 2019-07-21 09:04:24 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: Add Sasha as a stable branch maintainer 2018-12-01 09:42:50 +01:00
Makefile kbuild: initialize CLANG_FLAGS correctly in the top Makefile 2019-08-06 19:05:25 +02:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.