[PATCH v2 09/22] x86/uaccess: Remove redundant CLACs in getuser/putuser error paths

From: Josh Poimboeuf <jpoimboe@redhat.com>
To: x86@kernel.org
Cc: linux-kernel@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Arnd Bergmann <arnd@arndb.de>, Jann Horn <jannh@google.com>,
	Randy Dunlap <rdunlap@infradead.org>
Subject: [PATCH v2 09/22] x86/uaccess: Remove redundant CLACs in getuser/putuser error paths
Date: Wed, 17 Jul 2019 20:36:44 -0500	[thread overview]
Message-ID: <bc14ded2755ae75bd9010c446079e113dbddb74b.1563413318.git.jpoimboe@redhat.com> (raw)
In-Reply-To: <cover.1563413318.git.jpoimboe@redhat.com>

The same getuser/putuser error paths are used regardless of whether AC
is set.  In non-exception failure cases, this results in an unnecessary
CLAC.

Fixes the following warnings:

  arch/x86/lib/getuser.o: warning: objtool: .altinstr_replacement+0x18: redundant UACCESS disable
  arch/x86/lib/putuser.o: warning: objtool: .altinstr_replacement+0x18: redundant UACCESS disable

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/lib/getuser.S | 20 ++++++++++----------
 arch/x86/lib/putuser.S | 29 ++++++++++++++++-------------
 2 files changed, 26 insertions(+), 23 deletions(-)

diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index 74fdff968ea3..304f958c27b2 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -115,29 +115,29 @@ ENDPROC(__get_user_8)
 EXPORT_SYMBOL(__get_user_8)
 
 
+bad_get_user_clac:
+	ASM_CLAC
 bad_get_user:
 	xor %edx,%edx
 	mov $(-EFAULT),%_ASM_AX
-	ASM_CLAC
 	ret
-END(bad_get_user)
 
 #ifdef CONFIG_X86_32
+bad_get_user_8_clac:
+	ASM_CLAC
 bad_get_user_8:
 	xor %edx,%edx
 	xor %ecx,%ecx
 	mov $(-EFAULT),%_ASM_AX
-	ASM_CLAC
 	ret
-END(bad_get_user_8)
 #endif
 
-	_ASM_EXTABLE_UA(1b, bad_get_user)
-	_ASM_EXTABLE_UA(2b, bad_get_user)
-	_ASM_EXTABLE_UA(3b, bad_get_user)
+	_ASM_EXTABLE_UA(1b, bad_get_user_clac)
+	_ASM_EXTABLE_UA(2b, bad_get_user_clac)
+	_ASM_EXTABLE_UA(3b, bad_get_user_clac)
 #ifdef CONFIG_X86_64
-	_ASM_EXTABLE_UA(4b, bad_get_user)
+	_ASM_EXTABLE_UA(4b, bad_get_user_clac)
 #else
-	_ASM_EXTABLE_UA(4b, bad_get_user_8)
-	_ASM_EXTABLE_UA(5b, bad_get_user_8)
+	_ASM_EXTABLE_UA(4b, bad_get_user_8_clac)
+	_ASM_EXTABLE_UA(5b, bad_get_user_8_clac)
 #endif
diff --git a/arch/x86/lib/putuser.S b/arch/x86/lib/putuser.S
index d2e5c9c39601..14bf78341d3c 100644
--- a/arch/x86/lib/putuser.S
+++ b/arch/x86/lib/putuser.S
@@ -32,8 +32,6 @@
  */
 
 #define ENTER	mov PER_CPU_VAR(current_task), %_ASM_BX
-#define EXIT	ASM_CLAC ;	\
-		ret
 
 .text
 ENTRY(__put_user_1)
@@ -43,7 +41,8 @@ ENTRY(__put_user_1)
 	ASM_STAC
 1:	movb %al,(%_ASM_CX)
 	xor %eax,%eax
-	EXIT
+	ASM_CLAC
+	ret
 ENDPROC(__put_user_1)
 EXPORT_SYMBOL(__put_user_1)
 
@@ -56,7 +55,8 @@ ENTRY(__put_user_2)
 	ASM_STAC
 2:	movw %ax,(%_ASM_CX)
 	xor %eax,%eax
-	EXIT
+	ASM_CLAC
+	ret
 ENDPROC(__put_user_2)
 EXPORT_SYMBOL(__put_user_2)
 
@@ -69,7 +69,8 @@ ENTRY(__put_user_4)
 	ASM_STAC
 3:	movl %eax,(%_ASM_CX)
 	xor %eax,%eax
-	EXIT
+	ASM_CLAC
+	ret
 ENDPROC(__put_user_4)
 EXPORT_SYMBOL(__put_user_4)
 
@@ -85,19 +86,21 @@ ENTRY(__put_user_8)
 5:	movl %edx,4(%_ASM_CX)
 #endif
 	xor %eax,%eax
-	EXIT
+	ASM_CLAC
+	RET
 ENDPROC(__put_user_8)
 EXPORT_SYMBOL(__put_user_8)
 
+bad_put_user_clac:
+	ASM_CLAC
 bad_put_user:
 	movl $-EFAULT,%eax
-	EXIT
-END(bad_put_user)
+	RET
 
-	_ASM_EXTABLE_UA(1b, bad_put_user)
-	_ASM_EXTABLE_UA(2b, bad_put_user)
-	_ASM_EXTABLE_UA(3b, bad_put_user)
-	_ASM_EXTABLE_UA(4b, bad_put_user)
+	_ASM_EXTABLE_UA(1b, bad_put_user_clac)
+	_ASM_EXTABLE_UA(2b, bad_put_user_clac)
+	_ASM_EXTABLE_UA(3b, bad_put_user_clac)
+	_ASM_EXTABLE_UA(4b, bad_put_user_clac)
 #ifdef CONFIG_X86_32
-	_ASM_EXTABLE_UA(5b, bad_put_user)
+	_ASM_EXTABLE_UA(5b, bad_put_user_clac)
 #endif
-- 
2.20.1

