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Mark Rutland 7b5a52cf25 arm64/fpsimd: signal: Fix restoration of SVE context 
commit d2907cbe9e upstream.

When SME is supported, Restoring SVE signal context can go wrong in a
few ways, including placing the task into an invalid state where the
kernel may read from out-of-bounds memory (and may potentially take a
fatal fault) and/or may kill the task with a SIGKILL.

(1) Restoring a context with SVE_SIG_FLAG_SM set can place the task into
    an invalid state where SVCR.SM is set (and sve_state is non-NULL)
    but TIF_SME is clear, consequently resuting in out-of-bounds memory
    reads and/or killing the task with SIGKILL.

    This can only occur in unusual (but legitimate) cases where the SVE
    signal context has either been modified by userspace or was saved in
    the context of another task (e.g. as with CRIU), as otherwise the
    presence of an SVE signal context with SVE_SIG_FLAG_SM implies that
    TIF_SME is already set.

    While in this state, task_fpsimd_load() will NOT configure SMCR_ELx
    (leaving some arbitrary value configured in hardware) before
    restoring SVCR and attempting to restore the streaming mode SVE
    registers from memory via sve_load_state(). As the value of
    SMCR_ELx.LEN may be larger than the task's streaming SVE vector
    length, this may read memory outside of the task's allocated
    sve_state, reading unrelated data and/or triggering a fault.

    While this can result in secrets being loaded into streaming SVE
    registers, these values are never exposed. As TIF_SME is clear,
    fpsimd_bind_task_to_cpu() will configure CPACR_ELx.SMEN to trap EL0
    accesses to streaming mode SVE registers, so these cannot be
    accessed directly at EL0. As fpsimd_save_user_state() verifies the
    live vector length before saving (S)SVE state to memory, no secret
    values can be saved back to memory (and hence cannot be observed via
    ptrace, signals, etc).

    When the live vector length doesn't match the expected vector length
    for the task, fpsimd_save_user_state() will send a fatal SIGKILL
    signal to the task. Hence the task may be killed after executing
    userspace for some period of time.

(2) Restoring a context with SVE_SIG_FLAG_SM clear does not clear the
    task's SVCR.SM. If SVCR.SM was set prior to restoring the context,
    then the task will be left in streaming mode unexpectedly, and some
    register state will be combined inconsistently, though the task will
    be left in legitimate state from the kernel's PoV.

    This can only occur in unusual (but legitimate) cases where ptrace
    has been used to set SVCR.SM after entry to the sigreturn syscall,
    as syscall entry clears SVCR.SM.

    In these cases, the the provided SVE register data will be loaded
    into the task's sve_state using the non-streaming SVE vector length
    and the FPSIMD registers will be merged into this using the
    streaming SVE vector length.

Fix (1) by setting TIF_SME when setting SVCR.SM. This also requires
ensuring that the task's sme_state has been allocated, but as this could
contain live ZA state, it should not be zeroed. Fix (2) by clearing
SVCR.SM when restoring a SVE signal context with SVE_SIG_FLAG_SM clear.

For consistency, I've pulled the manipulation of SVCR, TIF_SVE, TIF_SME,
and fp_type earlier, immediately after the allocation of
sve_state/sme_state, before the restore of the actual register state.
This makes it easier to ensure that these are always modified
consistently, even if a fault is taken while reading the register data
from the signal context. I do not expect any software to depend on the
exact state restored when a fault is taken while reading the context.

Fixes: 85ed24dad2 ("arm64/sme: Implement streaming SVE signal handling")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: <stable@vger.kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-01-30 10:32:24 +01:00
arch arm64/fpsimd: signal: Fix restoration of SVE context 2026-01-30 10:32:24 +01:00
block block: zero non-PI portion of auto integrity buffer 2026-01-23 11:21:16 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-30 10:32:12 +01:00
Documentation fou: Don't allow 0 for FOU_ATTR_IPPROTO. 2026-01-30 10:32:12 +01:00
drivers wifi: rsi: Fix memory corruption due to not set vif driver data size 2026-01-30 10:32:24 +01:00
fs fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes() 2026-01-30 10:32:15 +01:00
include mm/hugetlb: fix hugetlb_pmd_shared() 2026-01-30 10:32:15 +01:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring/io-wq: check IO_WQ_BIT_EXIT inside work run loop 2026-01-30 10:32:15 +01:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel panic: only warn about deprecated panic_print on write access 2026-01-30 10:32:22 +01:00
lib lib/buildid: use __kernel_read() for sleepable context 2026-01-23 11:21:25 +01:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm migrate: correct lock ordering for hugetlb file folios 2026-01-30 10:32:22 +01:00
net net/sched: act_ife: avoid possible NULL deref 2026-01-30 10:32:21 +01:00
rust rust: bitops: fix missing _find_* functions on 32-bit ARM 2026-01-23 11:21:12 +01:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:17:11 +01:00
scripts kconfig: fix static linking of nconf 2026-01-30 10:32:16 +01:00
security keys/trusted_keys: fix handle passed to tpm_buf_append_name during unseal 2026-01-30 10:32:22 +01:00
sound ALSA: usb-audio: Fix use-after-free in snd_usb_mixer_free() 2026-01-30 10:32:23 +01:00
tools vsock/test: fix seqpacket message bounds test 2026-01-30 10:32:21 +01:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: Fix last_boosted_vcpu index assignment bug 2026-01-02 12:57:21 +01:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS soc: fixes for 6.18, part 4 2025-11-28 09:57:31 -08:00
Makefile Linux 6.18.7 2026-01-23 11:21:37 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.