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arm64/fpsimd: ptrace: Mandate SVE payload for streaming-mode state

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When a task has PSTATE.SM==1, reads of NT_ARM_SSVE are required to
always present a header with SVE_PT_REGS_SVE, and register data in SVE
format. Reads of NT_ARM_SSVE must never present register data in FPSIMD
format. Within the kernel, we always expect streaming SVE data to be
stored in SVE format.

Currently a user can write to NT_ARM_SSVE with a header presenting
SVE_PT_REGS_FPSIMD rather than SVE_PT_REGS_SVE, placing the task's
FPSIMD/SVE data into an invalid state.

To fix this we can either:

(a) Forbid such writes.
(b) Accept such writes, and immediately convert data into SVE format.

Take the simple option and forbid such writes.

Fixes: e12310a0d3 ("arm64/sme: Implement ptrace support for streaming mode SVE registers")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Spickett <david.spickett@arm.com>
Cc: Luis Machado <luis.machado@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250508132644.1395904-19-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2025-05-08 14:26:38 +01:00 committed by Will Deacon
parent b93e685ecf
commit f916dd32a9
1 changed files with 11 additions and 1 deletions
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12
arch/arm64/kernel/ptrace.c
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@ -890,6 +890,7 @@ static int sve_set_common(struct task_struct *target,
struct user_sve_header header;
unsigned int vq;
unsigned long start, end;
bool fpsimd;
/* Header */
if (count < sizeof(header))
@ -899,6 +900,15 @@ static int sve_set_common(struct task_struct *target,
if (ret)
goto out;
/*
* Streaming SVE data is always stored and presented in SVE format.
* Require the user to provide SVE formatted data for consistency, and
* to avoid the risk that we configure the task into an invalid state.
*/
fpsimd = (header.flags & SVE_PT_REGS_MASK) == SVE_PT_REGS_FPSIMD;
if (fpsimd && type == ARM64_VEC_SME)
return -EINVAL;
/*
* Apart from SVE_PT_REGS_MASK, all SVE_PT_* flags are consumed by
* vec_set_vector_length(), which will also validate them for us:
@ -945,7 +955,7 @@ static int sve_set_common(struct task_struct *target,
/* Registers: FPSIMD-only case */
BUILD_BUG_ON(SVE_PT_FPSIMD_OFFSET != sizeof(header));
if ((header.flags & SVE_PT_REGS_MASK) == SVE_PT_REGS_FPSIMD) {
if (fpsimd) {
clear_tsk_thread_flag(target, TIF_SVE);
target->thread.fp_type = FP_STATE_FPSIMD;
ret = __fpr_set(target, regset, pos, count, kbuf, ubuf,