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Sean Christopherson 46a986888a x86/umip: Check that the instruction opcode is at least two bytes 
commit 32278c6779 upstream.

When checking for a potential UMIP violation on #GP, verify the decoder found
at least two opcode bytes to avoid false positives when the kernel encounters
an unknown instruction that starts with 0f.  Because the array of opcode.bytes
is zero-initialized by insn_init(), peeking at bytes[1] will misinterpret
garbage as a potential SLDT or STR instruction, and can incorrectly trigger
emulation.

E.g. if a VPALIGNR instruction

   62 83 c5 05 0f 08 ff     vpalignr xmm17{k5},xmm23,XMMWORD PTR [r8],0xff

hits a #GP, the kernel emulates it as STR and squashes the #GP (and corrupts
the userspace code stream).

Arguably the check should look for exactly two bytes, but no three byte
opcodes use '0f 00 xx' or '0f 01 xx' as an escape, i.e. it should be
impossible to get a false positive if the first two opcode bytes match '0f 00'
or '0f 01'.  Go with a more conservative check with respect to the existing
code to minimize the chances of breaking userspace, e.g. due to decoder
weirdness.

Analyzed by Nick Bray <ncbray@google.com>.

Fixes: 1e5db22369 ("x86/umip: Add emulation code for UMIP instructions")
Reported-by: Dan Snyder <dansnyder@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-10-19 16:21:48 +02:00
arch
block block: use int to store blk_stack_limits() return value 2025-10-19 16:21:30 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-19 16:21:43 +02:00
Documentation drm/vmwgfx: Copy DRM hash-table code into driver 2025-10-19 16:21:41 +02:00
drivers spi: cadence-quadspi: Flush posted register writes before DAC access 2025-10-19 16:21:48 +02:00
fs openat2: don't trigger automounts with RESOLVE_NO_XDEV 2025-10-19 16:21:46 +02:00
include scsi: libsas: Add sas_task_find_rq() 2025-10-19 16:21:40 +02:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:21:45 +02:00
io_uring io_uring: fix possible deadlock in io_register_iowq_max_workers() 2024-11-17 15:06:25 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:05:26 +01:00
kernel copy_sighand: Handle architectures where sizeof(unsigned long) < sizeof(u64) 2025-10-19 16:21:44 +02:00
lib lib/genalloc: fix device leak in of_gen_pool_get() 2025-10-19 16:21:45 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: hugetlb: avoid soft lockup when mprotect to large memory area 2025-10-19 16:21:38 +02:00
net sctp: Fix MAC comparison to be constant-time 2025-10-19 16:21:46 +02:00
samples samples: mei: Fix building on musl libc 2025-08-28 16:24:07 +02:00
scripts randstruct: gcc-plugin: Fix attribute addition 2025-09-09 18:50:23 +02:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-19 16:21:45 +02:00
sound ASoC: Intel: bytcr_rt5651: Fix invalid quirk input mapping 2025-10-19 16:21:34 +02:00
tools rseq/selftests: Use weak symbol reference, not definition, to link with glibc 2025-10-19 16:21:47 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:05:22 +01:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-10-22 15:40:41 +02:00
.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 Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.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 trace: Relocate event helper files 2024-04-10 16:19:24 +02:00
Makefile Linux 5.15.194 2025-10-02 13:39:15 +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.