x86/fpu: Use validate_xstate_header() to validate the xstate_header in copy_user_to_xstate()

Tighten the checks in copy_user_to_xstate().
Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Kevin Hao <haokexin@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Halcrow <mhalcrow@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: kernel-hardening@lists.openwall.com
Link: http://lkml.kernel.org/r/20170924105913.9157-10-mingo@kernel.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/fpu/xstate.c

@@ -1188,16 +1188,15 @@ int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf)
 }
 
 /*
- * Convert from a ptrace standard-format user-space buffer to kernel XSAVES format
- * and copy to the target thread. This is called from xstateregs_set() and
- * there we check the CPU has XSAVES and a whole standard-sized buffer
- * exists.
+ * Convert from a ptrace or sigreturn standard-format user-space buffer to
+ * kernel XSAVES format and copy to the target thread. This is called from
+ * xstateregs_set(), as well as potentially from the sigreturn() and
+ * rt_sigreturn() system calls.
  */
 int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf)
 {
 	unsigned int offset, size;
 	int i;
-	u64 allowed_features;
 	struct xstate_header hdr;
 
 	offset = offsetof(struct xregs_state, header);
@@ -1206,12 +1205,7 @@ int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf)
 	if (__copy_from_user(&hdr, ubuf + offset, size))
 		return -EFAULT;
 
-	/*
-	 * Reject if the user sets any disabled or supervisor features:
-	 */
-	allowed_features = xfeatures_mask & ~XFEATURE_MASK_SUPERVISOR;
-
-	if (hdr.xfeatures & ~allowed_features)
+	if (validate_xstate_header(&hdr))
 		return -EINVAL;
 
 	for (i = 0; i < XFEATURE_MAX; i++) {