linux-kernel - [tip: x86/urgent] x86/uaccess: Don't leak the AC flags into __get

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Message-ID: <156742768563.30370.14506895450404848829.tip-bot2@tip-bot2>
Date:   Mon, 02 Sep 2019 12:34:45 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, broonie@...nel.org,
        sfr@...b.auug.org.au, akpm@...ux-foundation.org, mhocko@...e.cz,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/uaccess: Don't leak the AC flags into
 __get_user() argument evaluation

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     9b8bd476e78e89c9ea26c3b435ad0201c3d7dbf5
Gitweb:        https://git.kernel.org/tip/9b8bd476e78e89c9ea26c3b435ad0201c3d7dbf5
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Thu, 29 Aug 2019 10:24:45 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 02 Sep 2019 14:22:38 +02:00

x86/uaccess: Don't leak the AC flags into __get_user() argument evaluation

Identical to __put_user(); the __get_user() argument evalution will too
leak UBSAN crud into the __uaccess_begin() / __uaccess_end() region.
While uncommon this was observed to happen for:

  drivers/xen/gntdev.c: if (__get_user(old_status, batch->status[i]))

where UBSAN added array bound checking.

This complements commit:

  6ae865615fc4 ("x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation")

Tested-by Sedat Dilek <sedat.dilek@...il.com>
Reported-by: Randy Dunlap <rdunlap@...radead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: broonie@...nel.org
Cc: sfr@...b.auug.org.au
Cc: akpm@...ux-foundation.org
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: mhocko@...e.cz
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lkml.kernel.org/r/20190829082445.GM2369@hirez.programming.kicks-ass.net
---
 arch/x86/include/asm/uaccess.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 9c44353..35c225e 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -444,8 +444,10 @@ __pu_label:							\
 ({									\
 	int __gu_err;							\
 	__inttype(*(ptr)) __gu_val;					\
+	__typeof__(ptr) __gu_ptr = (ptr);				\
+	__typeof__(size) __gu_size = (size);				\
 	__uaccess_begin_nospec();					\
-	__get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT);	\
+	__get_user_size(__gu_val, __gu_ptr, __gu_size, __gu_err, -EFAULT);	\
 	__uaccess_end();						\
 	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
 	__builtin_expect(__gu_err, 0);					\