Commit f916dd32 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
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arm64/fpsimd: ptrace: Mandate SVE payload for streaming-mode state 



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: e12310a0 ("arm64/sme: Implement ptrace support for streaming mode SVE registers")
Signed-off-by: default avatarMark 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: default avatarMark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250508132644.1395904-19-mark.rutland@arm.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent b93e685e

arch/arm64/kernel/ptrace.c

+11 −1
Original line number Diff line number Diff line
@@ -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,