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Mark Rutland 2305b809be arm64: uaccess: simplify uaccess_mask_ptr() 
We introduced uaccess pointer masking for arm64 in commit:

  4d8efc2d5e ("arm64: Use pointer masking to limit uaccess speculation")

Which was intended to prevent speculative uaccesses to kernel memory on
CPUs where access permissions were not respected under speculation.

At the time, the uaccess primitives were occasionally used to access
kernel memory, with the maximum permitted address held in
thread_info::addr_limit. Consequently, the address masking needed to
take this dynamic limit into account.

Subsequently the uaccess primitives were reworked such that they are
only used for user memory, and as of commit:

  3d2403fd10 ("arm64: uaccess: remove set_fs()")

... the address limit was made a compile-time constant, but the logic
was otherwise unchanged.

Regardless of the configured VA size or whether TBI is in use, the
address space can be divided into three ranges:

* The TTBR0 VA range, for which any valid pointer has bit 55 *clear*,
  and any non-tag bits [63-56] must match bit 55 (i.e. must be clear).

* The TTBR1 VA range, for which any valid pointer has bit 55 *set*, and
  any non-tag bits [63-56] must match bit 55 (i.e. must be set).

* The gap between the TTBR0 and TTBR1 ranges, where bit 55 may be set or
  clear, but any access will result in a fault.

As the uaccess primitives are now only used for user memory in the TTBR0
VA range, we can prevent generation of TTBR1 addresses by clearing bit
55, which will either result in a TTBR0 address or a faulting address
between the TTBR VA ranges.

This is beneficial for code generation as:

* We no longer clobber the condition codes.

* We no longer burn a register on (TASK_SIZE_MAX - 1).

* We no longer need to consume the untagged pointer.

When building a defconfig v6.0-rc3 with GCC 12.1.0, this change makes
the resulting Image 64KiB smaller.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20220922151053.3520750-1-mark.rutland@arm.com
[catalin.marinas@arm.com: remove csdb() as the bit clearing is unconditional]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
 		2022-09-23 14:39:20 +01:00
Documentation arm64: support huge vmalloc mappings 2022-09-16 09:51:28 +01:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
arch arm64: uaccess: simplify uaccess_mask_ptr() 2022-09-23 14:39:20 +01:00
block block-6.0-2022-08-26 2022-08-26 11:05:54 -07:00
certs Kbuild updates for v5.20 2022-08-10 10:40:41 -07:00
crypto crypto: blake2b: effectively disable frame size warning 2022-08-10 17:59:11 -07:00
drivers Seventeen hotfixes. Mostly memory management things. Ten patches are 2022-08-28 14:49:59 -07:00
fs Seventeen hotfixes. Mostly memory management things. Ten patches are 2022-08-28 14:49:59 -07:00
include Seventeen hotfixes. Mostly memory management things. Ten patches are 2022-08-28 14:49:59 -07:00
init arm64 fixes for -rc3 2022-08-26 11:32:53 -07:00
io_uring io_uring/net: save address for sendzc async execution 2022-08-25 07:52:30 -06:00
ipc Updates to various subsystems which I help look after. lib, ocfs2, 2022-08-07 10:03:24 -07:00
kernel Seventeen hotfixes. Mostly memory management things. Ten patches are 2022-08-28 14:49:59 -07:00
lib bitmap fixes for v6.0-rc3 2022-08-28 14:36:27 -07:00
mm mm/mprotect: only reference swap pfn page if type match 2022-08-28 14:02:46 -07:00
net Including fixes from ipsec and netfilter (with one broken Fixes tag). 2022-08-25 14:03:58 -07:00
samples Tracing updates for 5.20 / 6.0 2022-08-05 09:41:12 -07:00
scripts asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
security hardening fixes for v6.0-rc2 2022-08-19 13:56:14 -07:00
sound sound fixes for 6.0-rc2 2022-08-19 09:46:11 -07:00
tools Misc fixes: 2022-08-28 10:10:23 -07:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt KVM: Drop unnecessary initialization of "ops" in kvm_ioctl_create_device() 2022-08-19 04:05:43 -04:00
.clang-format PCI/DOE: Add DOE mailbox support functions 2022-07-19 15:38:04 -07:00
.cocciconfig
…
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap .mailmap: update Luca Ceresoli's e-mail address 2022-08-28 14:02:46 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS drm for 5.20/6.0 2022-08-03 19:52:08 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS bitmap fixes for v6.0-rc3 2022-08-28 14:36:27 -07:00
Makefile Linux 6.0-rc3 2022-08-28 15:05:29 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.