| Date | Wed, 23 Jun 2021 14:01:37 +0200 | From | Thomas Gleixner <> | Subject | [patch V4 10/65] x86/fpu: Reject invalid MXCSR values in copy_kernel_to_xstate() |
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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> Reviewed-by: Borislav Petkov <bp@suse.de> --- V3: Validate MXCSR when FP|SSE|YMM are set. The quirk check is only correct for the copy function. V2: New patch --- arch/x86/kernel/fpu/xstate.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-)
--- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -1154,6 +1154,19 @@ void copy_xstate_to_kernel(struct membuf 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_s 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_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; }
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