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The source for the Linux kernel used in Windows Subsystem for Linux 2 (WSL2)
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Marco Elver 8550c9b846 stack: Constrain and fix stack offset randomization with Clang builds 
[ Upstream commit efa90c11f6 ]

All supported versions of Clang perform auto-init of __builtin_alloca()
when stack auto-init is on (CONFIG_INIT_STACK_ALL_{ZERO,PATTERN}).

add_random_kstack_offset() uses __builtin_alloca() to add a stack
offset. This means, when CONFIG_INIT_STACK_ALL_{ZERO,PATTERN} is
enabled, add_random_kstack_offset() will auto-init that unused portion
of the stack used to add an offset.

There are several problems with this:

	1. These offsets can be as large as 1023 bytes. Performing
	   memset() on them isn't exactly cheap, and this is done on
	   every syscall entry.

	2. Architectures adding add_random_kstack_offset() to syscall
	   entry implemented in C require them to be 'noinstr' (e.g. see
	   x86 and s390). The potential problem here is that a call to
	   memset may occur, which is not noinstr.

A x86_64 defconfig kernel with Clang 11 and CONFIG_VMLINUX_VALIDATION shows:

 | vmlinux.o: warning: objtool: do_syscall_64()+0x9d: call to memset() leaves .noinstr.text section
 | vmlinux.o: warning: objtool: do_int80_syscall_32()+0xab: call to memset() leaves .noinstr.text section
 | vmlinux.o: warning: objtool: __do_fast_syscall_32()+0xe2: call to memset() leaves .noinstr.text section
 | vmlinux.o: warning: objtool: fixup_bad_iret()+0x2f: call to memset() leaves .noinstr.text section

Clang 14 (unreleased) will introduce a way to skip alloca initialization
via __builtin_alloca_uninitialized() (https://reviews.llvm.org/D115440).

Constrain RANDOMIZE_KSTACK_OFFSET to only be enabled if no stack
auto-init is enabled, the compiler is GCC, or Clang is version 14+. Use
__builtin_alloca_uninitialized() if the compiler provides it, as is done
by Clang 14.

Link: https://lkml.kernel.org/r/YbHTKUjEejZCLyhX@elver.google.com
Fixes: 39218ff4c6 ("stack: Optionally randomize kernel stack offset each syscall")
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220131090521.1947110-2-elver@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2022-04-08 14:23:06 +02:00
Documentation Documentation: update stable tree link 2022-04-08 14:22:51 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
arch stack: Constrain and fix stack offset randomization with Clang builds 2022-04-08 14:23:06 +02:00
block block: don't merge across cgroup boundaries if blkcg is enabled 2022-04-08 14:22:59 +02:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto crypto: authenc - Fix sleep in atomic context in decrypt_tail 2022-04-08 14:23:05 +02:00
drivers spi: tegra210-quad: Fix missin IRQ check in tegra_qspi_probe 2022-04-08 14:23:06 +02:00
fs btrfs: verify the tranisd of the to-be-written dirty extent buffer 2022-04-08 14:23:02 +02:00
include stack: Constrain and fix stack offset randomization with Clang builds 2022-04-08 14:23:06 +02:00
init init: make unknown command line param message clearer 2021-11-18 19:17:11 +01:00
ipc ipc/sem: do not sleep with a spin lock held 2022-02-08 18:34:03 +01:00
kernel tracing: Have trace event string test handle zero length strings 2022-04-08 14:22:57 +02:00
lib lib/raid6/test: fix multiple definition linking error 2022-04-08 14:23:01 +02:00
mm mm/kmemleak: reset tag when compare object pointer 2022-04-08 14:22:56 +02:00
net rfkill: make new event layout opt-in 2022-04-08 14:23:00 +02:00
samples samples/landlock: Fix path_list memory leak 2022-04-08 14:22:59 +02:00
scripts kconfig: fix failing to generate auto.conf 2022-02-23 12:03:20 +01:00
security selinux: Fix selinux_sb_mnt_opts_compat() 2022-04-08 14:23:05 +02:00
sound ASoC: SOF: Intel: Fix NULL ptr dereference when ENOMEM 2022-04-08 14:22:58 +02:00
tools selftests: vm: fix clang build error multiple output files 2022-04-08 14:22:48 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Fix lockdep false negative during host resume 2022-03-16 14:23:40 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
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 MAINTAINERS: adjust file entry for of_net.c after movement 2022-03-08 19:12:53 +01:00
Makefile Linux 5.15.32 2022-03-28 09:58:46 +02:00
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.