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

Tighten the checks in xstateregs_set().
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/20170924105913.9157-3-mingo@kernel.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/fpu/regset.c

@@ -141,27 +141,20 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
 			ret = copy_user_to_xstate(xsave, ubuf);
 	} else {
 		ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, xsave, 0, -1);
-
-		/* xcomp_bv must be 0 when using uncompacted format */
-		if (!ret && xsave->header.xcomp_bv)
-			ret = -EINVAL;
+		if (!ret)
+			ret = validate_xstate_header(&xsave->header);
 	}
 
-	/*
-	 * In case of failure, mark all states as init:
-	 */
-	if (ret)
-		fpstate_init(&fpu->state);
-
 	/*
 	 * mxcsr reserved bits must be masked to zero for security reasons.
 	 */
 	xsave->i387.mxcsr &= mxcsr_feature_mask;
-	xsave->header.xfeatures &= xfeatures_mask;
+
 	/*
-	 * These bits must be zero.
+	 * In case of failure, mark all states as init:
 	 */
-	memset(&xsave->header.reserved, 0, 48);
+	if (ret)
+		fpstate_init(&fpu->state);
 
 	return ret;
 }