linux-kernel - [tip:x86/fpu] x86/fpu: Use validate_xstate_header() to validate the xstate_header in __fpu__restore

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Message-ID: <tip-b11e2e18a7fc8eaa3d592c260d50c7129e094ded@git.kernel.org>
Date:   Tue, 26 Sep 2017 01:35:10 -0700
From:   tip-bot for Eric Biggers <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, dvyukov@...gle.com, mingo@...nel.org,
        oleg@...hat.com, riel@...hat.com, yu-cheng.yu@...el.com,
        torvalds@...ux-foundation.org, hpa@...or.com, bp@...en8.de,
        peterz@...radead.org, keescook@...omium.org,
        linux-kernel@...r.kernel.org, haokexin@...il.com,
        dave.hansen@...ux.intel.com, wanpeng.li@...mail.com,
        fenghua.yu@...el.com, mhalcrow@...gle.com,
        akpm@...ux-foundation.org, luto@...capital.net,
        ebiggers@...gle.com, luto@...nel.org, ebiggers3@...il.com
Subject: [tip:x86/fpu] x86/fpu: Use validate_xstate_header() to validate the
 xstate_header in __fpu__restore_sig()

Commit-ID:  b11e2e18a7fc8eaa3d592c260d50c7129e094ded
Gitweb:     http://git.kernel.org/tip/b11e2e18a7fc8eaa3d592c260d50c7129e094ded
Author:     Eric Biggers <ebiggers@...gle.com>
AuthorDate: Sun, 24 Sep 2017 12:59:06 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 26 Sep 2017 09:43:46 +0200

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

Tighten the checks in __fpu__restore_sig() and update comments.

Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Eric Biggers <ebiggers3@...il.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Kevin Hao <haokexin@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Michael Halcrow <mhalcrow@...gle.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Wanpeng Li <wanpeng.li@...mail.com>
Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc: kernel-hardening@...ts.openwall.com
Link: http://lkml.kernel.org/r/20170924105913.9157-4-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/fpu/signal.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 7fa3bdb..fb639e7 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -214,8 +214,11 @@ sanitize_restored_xstate(struct task_struct *tsk,
 	struct xstate_header *header = &xsave->header;
 
 	if (use_xsave()) {
-		/* These bits must be zero. */
-		memset(header->reserved, 0, 48);
+		/*
+		 * Note: we don't need to zero the reserved bits in the
+		 * xstate_header here because we either didn't copy them at all,
+		 * or we checked earlier that they aren't set.
+		 */
 
 		/*
 		 * Init the state that is not present in the memory
@@ -224,7 +227,7 @@ sanitize_restored_xstate(struct task_struct *tsk,
 		if (fx_only)
 			header->xfeatures = XFEATURE_MASK_FPSSE;
 		else
-			header->xfeatures &= (xfeatures_mask & xfeatures);
+			header->xfeatures &= xfeatures;
 	}
 
 	if (use_fxsr()) {
@@ -308,7 +311,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		/*
 		 * For 32-bit frames with fxstate, copy the user state to the
 		 * thread's fpu state, reconstruct fxstate from the fsave
-		 * header. Sanitize the copied state etc.
+		 * header. Validate and sanitize the copied state.
 		 */
 		struct fpu *fpu = &tsk->thread.fpu;
 		struct user_i387_ia32_struct env;
@@ -329,9 +332,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		} else {
 			err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
 
-			/* xcomp_bv must be 0 when using uncompacted format */
-			if (!err && state_size > offsetof(struct xregs_state, header) && fpu->state.xsave.header.xcomp_bv)
-				err = -EINVAL;
+			if (!err && state_size > offsetof(struct xregs_state, header))
+				err = validate_xstate_header(&fpu->state.xsave.header);
 		}
 
 		if (err || __copy_from_user(&env, buf, sizeof(env))) {