linux-kernel - [PATCH 12/12] x86_64: __clear_user as case of __memset

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Message-Id: <20181219213338.26619-13-igor.stoppa@huawei.com>
Date:   Wed, 19 Dec 2018 23:33:38 +0200
From:   Igor Stoppa <igor.stoppa@...il.com>
To:     Andy Lutomirski <luto@...capital.net>,
        Matthew Wilcox <willy@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     igor.stoppa@...wei.com, Nadav Amit <nadav.amit@...il.com>,
        Kees Cook <keescook@...omium.org>,
        linux-integrity@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 12/12] x86_64: __clear_user as case of __memset_user

To avoid code duplication, re-use __memset_user(), when clearing
user-space memory.

The overhead should be minimal (2 extra register assignments) and
outside of the writing loop.

Signed-off-by: Igor Stoppa <igor.stoppa@...wei.com>

CC: Andy Lutomirski <luto@...capital.net>
CC: Nadav Amit <nadav.amit@...il.com>
CC: Matthew Wilcox <willy@...radead.org>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Kees Cook <keescook@...omium.org>
CC: Dave Hansen <dave.hansen@...ux.intel.com>
CC: Mimi Zohar <zohar@...ux.vnet.ibm.com>
CC: linux-integrity@...r.kernel.org
CC: kernel-hardening@...ts.openwall.com
CC: linux-mm@...ck.org
CC: linux-kernel@...r.kernel.org
---
 arch/x86/lib/usercopy_64.c | 29 +----------------------------
 1 file changed, 1 insertion(+), 28 deletions(-)

diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 84f8f8a20b30..ab6aabb62055 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -69,34 +69,7 @@ EXPORT_SYMBOL(memset_user);
 
 unsigned long __clear_user(void __user *addr, unsigned long size)
 {
-	long __d0;
-	might_fault();
-	/* no memory constraint because it doesn't change any memory gcc knows
-	   about */
-	stac();
-	asm volatile(
-		"	testq  %[size8],%[size8]\n"
-		"	jz     4f\n"
-		"0:	movq $0,(%[dst])\n"
-		"	addq   $8,%[dst]\n"
-		"	decl %%ecx ; jnz   0b\n"
-		"4:	movq  %[size1],%%rcx\n"
-		"	testl %%ecx,%%ecx\n"
-		"	jz     2f\n"
-		"1:	movb   $0,(%[dst])\n"
-		"	incq   %[dst]\n"
-		"	decl %%ecx ; jnz  1b\n"
-		"2:\n"
-		".section .fixup,\"ax\"\n"
-		"3:	lea 0(%[size1],%[size8],8),%[size8]\n"
-		"	jmp 2b\n"
-		".previous\n"
-		_ASM_EXTABLE_UA(0b, 3b)
-		_ASM_EXTABLE_UA(1b, 2b)
-		: [size8] "=&c"(size), [dst] "=&D" (__d0)
-		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));
-	clac();
-	return size;
+	return __memset_user(addr, 0, size);
 }
 EXPORT_SYMBOL(__clear_user);
 
-- 
2.19.1