Commit 947f4947 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Borislav Petkov
Browse files

x86/fpu: Reject invalid MXCSR values in copy_kernel_to_xstate() 



Instead of masking out reserved bits, check them and reject the provided
state as invalid if not zero.

Suggested-by: default avatarAndy Lutomirski <luto@kernel.org>
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/20210623121452.308388343@linutronix.de
parent 43be46e8

arch/x86/kernel/fpu/xstate.c

+16 −3
Original line number Diff line number Diff line
@@ -1154,6 +1154,19 @@ void copy_xstate_to_kernel(struct membuf to, struct xregs_state *xsave) 
		membuf_zero(&to, to.left);

}



static inline bool mxcsr_valid(struct xstate_header *hdr, const u32 *mxcsr)

{

	u64 mask = XFEATURE_MASK_FP | XFEATURE_MASK_SSE | XFEATURE_MASK_YMM;



	/* Only check if it is in use */

	if (hdr->xfeatures & mask) {

		/* Reserved bits in MXCSR must be zero. */

		if (*mxcsr & ~mxcsr_feature_mask)

			return false;

	}

	return true;

}



/*

 * Convert from a ptrace standard-format kernel buffer to kernel XSAVE[S] format

 * and copy to the target thread. This is called from xstateregs_set().
@@ -1172,6 +1185,9 @@ int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf) 
	if (validate_user_xstate_header(&hdr))

		return -EINVAL;



	if (!mxcsr_valid(&hdr, kbuf + offsetof(struct fxregs_state, mxcsr)))

		return -EINVAL;



	for (i = 0; i < XFEATURE_MAX; i++) {

		u64 mask = ((u64)1 << i);
@@ -1202,9 +1218,6 @@ int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf) 
	 */

	xsave->header.xfeatures |= hdr.xfeatures;



	/* mxcsr reserved bits must be masked to zero for historical reasons. */

	xsave->i387.mxcsr &= mxcsr_feature_mask;



	return 0;

}