Commit be625d80 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
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arm64/fpsimd: signal: Consistently read FPSIMD context 



For historical reasons, restore_sve_fpsimd_context() has an open-coded
copy of the logic from read_fpsimd_context(), which is used to either
restore an FPSIMD-only context, or to merge FPSIMD state into an
SVE state when restoring an SVE+FPSIMD context. The logic is *almost*
identical.

Refactor the logic to avoid duplication and make this clearer.

This comes with two functional changes that I do not believe will be
problematic in practice:

* The user_fpsimd_state::size field will be checked in all restore paths
  that consume it user_fpsimd_state. The kernel always populates this
  field when delivering a signal, and so this should contain the
  expected value unless it has been corrupted.

* If a read of user_fpsimd_state fails, we will return early without
  modifying TIF_SVE, the saved SVCR, or the save fp_type. This will
  leave the task in a consistent state, without potentially resurrecting
  stale FPSIMD state. A read of user_fpsimd_state should never fail
  unless the structure has been corrupted or the stack has been
  unmapped.

Suggested-by: default avatarWill Deacon <will@kernel.org>
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20250508132644.1395904-5-mark.rutland@arm.com


[will: Ensure read_fpsimd_context() returns negative error code or zero]
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent b465ace4

arch/arm64/kernel/signal.c

+29 −28
Original line number Diff line number Diff line
@@ -264,30 +264,40 @@ static int preserve_fpsimd_context(struct fpsimd_context __user *ctx) 
	return err ? -EFAULT : 0;

}



static int restore_fpsimd_context(struct user_ctxs *user)

static int read_fpsimd_context(struct user_fpsimd_state *fpsimd,

			       struct user_ctxs *user)

{

	struct user_fpsimd_state fpsimd;

	int err = 0;

	int err;



	/* check the size information */

	if (user->fpsimd_size != sizeof(struct fpsimd_context))

		return -EINVAL;



	/* copy the FP and status/control registers */

	err = __copy_from_user(fpsimd.vregs, &(user->fpsimd->vregs),

			       sizeof(fpsimd.vregs));

	__get_user_error(fpsimd.fpsr, &(user->fpsimd->fpsr), err);

	__get_user_error(fpsimd.fpcr, &(user->fpsimd->fpcr), err);

	err = __copy_from_user(fpsimd->vregs, &(user->fpsimd->vregs),

			       sizeof(fpsimd->vregs));

	__get_user_error(fpsimd->fpsr, &(user->fpsimd->fpsr), err);

	__get_user_error(fpsimd->fpcr, &(user->fpsimd->fpcr), err);



	return err ? -EFAULT : 0;

}



static int restore_fpsimd_context(struct user_ctxs *user)

{

	struct user_fpsimd_state fpsimd;

	int err;



	err = read_fpsimd_context(&fpsimd, user);

	if (err)

		return err;



	clear_thread_flag(TIF_SVE);

	current->thread.svcr &= ~SVCR_SM_MASK;

	current->thread.fp_type = FP_STATE_FPSIMD;



	/* load the hardware registers from the fpsimd_state structure */

	if (!err)

	fpsimd_update_current_state(&fpsimd);



	return err ? -EFAULT : 0;

	return 0;

}



static int preserve_fpmr_context(struct fpmr_context __user *ctx)
@@ -427,12 +437,8 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user) 
	 * consistency and robustness, reject restoring streaming SVE state

	 * without an SVE payload.

	 */

	if (!sm && user->sve_size == sizeof(*user->sve)) {

		clear_thread_flag(TIF_SVE);

		current->thread.svcr &= ~SVCR_SM_MASK;

		current->thread.fp_type = FP_STATE_FPSIMD;

		goto fpsimd_only;

	}

	if (!sm && user->sve_size == sizeof(*user->sve))

		return restore_fpsimd_context(user);



	vq = sve_vq_from_vl(vl);
@@ -458,19 +464,14 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user) 
		set_thread_flag(TIF_SVE);

	current->thread.fp_type = FP_STATE_SVE;



fpsimd_only:

	/* copy the FP and status/control registers */

	/* restore_sigframe() already checked that user->fpsimd != NULL. */

	err = __copy_from_user(fpsimd.vregs, user->fpsimd->vregs,

			       sizeof(fpsimd.vregs));

	__get_user_error(fpsimd.fpsr, &user->fpsimd->fpsr, err);

	__get_user_error(fpsimd.fpcr, &user->fpsimd->fpcr, err);

	err = read_fpsimd_context(&fpsimd, user);

	if (err)

		return err;



	/* load the hardware registers from the fpsimd_state structure */

	if (!err)

	/* Merge the FPSIMD registers into the SVE state */

	fpsimd_update_current_state(&fpsimd);



	return err ? -EFAULT : 0;

	return 0;

}



#else /* ! CONFIG_ARM64_SVE */