[patch V2 09/52] x86/fpu: Reject invalid MXCSR values in copy_kernel_to_xstate()

Thomas Gleixner
2021-06-14T16:38:27Z

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

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: New patch
---
arch/x86/kernel/fpu/xstate.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1166,6 +1166,14 @@ int copy_kernel_to_xstate(struct xregs_s
if (validate_user_xstate_header(&hdr))
return -EINVAL;

+ if (xfeatures_mxcsr_quirk(hdr.xfeatures)) {
+ const u32 *mxcsr = kbuf + offsetof(struct fxregs_state, mxcsr);
+
+ /* Reserved bits in MXCSR must be zero. */
+ if (*mxcsr & ~mxcsr_feature_mask)
+ return -EINVAL;
+ }
+
for (i = 0; i < XFEATURE_MAX; i++) {
u64 mask = ((u64)1 << i);

@@ -1196,9 +1204,6 @@ int copy_kernel_to_xstate(struct xregs_s
*/
xsave->header.xfeatures |= hdr.xfeatures;

- /* mxcsr reserved bits must be masked to zero for historical reasons. */
- xsave->i387.mxcsr &= mxcsr_feature_mask;
-
return 0;
}