Commit 6f9866a1 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Borislav Petkov
Browse files

x86/fpu/signal: Let xrstor handle the features to init 



There is no reason to do an extra XRSTOR from init_fpstate for feature
bits which have been cleared by user space in the FX magic xfeatures
storage.

Just clear them in the task's XSTATE header and do a full restore which
will put these cleared features into init state.

There is no real difference in performance because the current code
already does a full restore when the xfeatures bits are preserved as the
signal frame setup has stored them, which is the full UABI feature set.

 [ bp: Use the negated mxcsr_feature_mask in the MXCSR check. ]

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121457.804115017@linutronix.de
parent fcb3635f

arch/x86/kernel/fpu/signal.c

+31 −58
Original line number Diff line number Diff line
@@ -220,36 +220,6 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size) 
	return 0;

}



static inline void

sanitize_restored_user_xstate(union fpregs_state *state,

			      struct user_i387_ia32_struct *ia32_env, u64 mask)

{

	struct xregs_state *xsave = &state->xsave;

	struct xstate_header *header = &xsave->header;



	if (use_xsave()) {

		/*

		 * Clear all feature bits which are not set in mask.

		 *

		 * Supervisor state has to be preserved. The sigframe

		 * restore can only modify user features, i.e. @mask

		 * cannot contain them.

		 */

		header->xfeatures &= mask | xfeatures_mask_supervisor();

	}



	if (use_fxsr()) {

		/*

		 * mscsr reserved bits must be masked to zero for security

		 * reasons.

		 */

		xsave->i387.mxcsr &= mxcsr_feature_mask;



		if (ia32_env)

			convert_to_fxsr(&state->fxsave, ia32_env);

	}

}



static int __restore_fpregs_from_user(void __user *buf, u64 xrestore,

				      bool fx_only)

{
@@ -352,6 +322,8 @@ static int __fpu_restore_sig(void __user *buf, void __user *buf_fx, 
		fx_only = !fx_sw_user.magic1;

		state_size = fx_sw_user.xstate_size;

		user_xfeatures = fx_sw_user.xfeatures;

	} else {

		user_xfeatures = XFEATURE_MASK_FPSSE;

	}



	if (likely(!ia32_fxstate)) {
@@ -395,54 +367,55 @@ static int __fpu_restore_sig(void __user *buf, void __user *buf_fx, 
		set_thread_flag(TIF_NEED_FPU_LOAD);

	}

	__fpu_invalidate_fpregs_state(fpu);

	__cpu_invalidate_fpregs_state();

	fpregs_unlock();



	if (use_xsave() && !fx_only) {

		u64 init_bv = xfeatures_mask_uabi() & ~user_xfeatures;



		ret = copy_sigframe_from_user_to_xstate(&fpu->state.xsave, buf_fx);

		if (ret)

			return ret;



		sanitize_restored_user_xstate(&fpu->state, &env, user_xfeatures);



		fpregs_lock();

		if (unlikely(init_bv))

			os_xrstor(&init_fpstate.xsave, init_bv);



		/*

		 * Restore previously saved supervisor xstates along with

		 * copied-in user xstates.

		 */

		ret = os_xrstor_safe(&fpu->state.xsave,

				     user_xfeatures | xfeatures_mask_supervisor());



	} else {

		ret = __copy_from_user(&fpu->state.fxsave, buf_fx, state_size);

		if (ret)

		if (__copy_from_user(&fpu->state.fxsave, buf_fx,

				     sizeof(fpu->state.fxsave)))

			return -EFAULT;



		sanitize_restored_user_xstate(&fpu->state, &env, user_xfeatures);

		/* Reject invalid MXCSR values. */

		if (fpu->state.fxsave.mxcsr & ~mxcsr_feature_mask)

			return -EINVAL;



		/* Enforce XFEATURE_MASK_FPSSE when XSAVE is enabled */

		if (use_xsave())

			fpu->state.xsave.header.xfeatures |= XFEATURE_MASK_FPSSE;

	}



	/* Fold the legacy FP storage */

	convert_to_fxsr(&fpu->state.fxsave, &env);



	fpregs_lock();

	if (use_xsave()) {

			u64 init_bv;



			init_bv = xfeatures_mask_uabi() & ~XFEATURE_MASK_FPSSE;

			os_xrstor(&init_fpstate.xsave, init_bv);

		}

		/*

		 * Remove all UABI feature bits not set in user_xfeatures

		 * from the memory xstate header which makes the full

		 * restore below bring them into init state. This works for

		 * fx_only mode as well because that has only FP and SSE

		 * set in user_xfeatures.

		 *

		 * Preserve supervisor states!

		 */

		u64 mask = user_xfeatures | xfeatures_mask_supervisor();



		fpu->state.xsave.header.xfeatures &= mask;

		ret = os_xrstor_safe(&fpu->state.xsave, xfeatures_mask_all);

	} else {

		ret = fxrstor_safe(&fpu->state.fxsave);

	}



	if (!ret)

	if (likely(!ret))

		fpregs_mark_activate();

	else

		fpregs_deactivate(fpu);



	fpregs_unlock();

	return ret;

}



static inline int xstate_sigframe_size(void)

{

	return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :