linux-kernel - [tip:x86/asm] x86/asm/entry/32: Open-code CLEAR

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Message-ID: <tip-ef0cd5dc25404594f832dad9133abae52e3b2fa3@git.kernel.org>
Date:	Sun, 7 Jun 2015 01:31:19 -0700
From:	tip-bot for Denys Vlasenko <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	fweisbec@...il.com, peterz@...radead.org, ast@...mgrid.com,
	linux-kernel@...r.kernel.org, oleg@...hat.com, brgerst@...il.com,
	keescook@...omium.org, rostedt@...dmis.org, tglx@...utronix.de,
	wad@...omium.org, akpm@...ux-foundation.org, mingo@...nel.org,
	luto@...capital.net, torvalds@...ux-foundation.org, hpa@...or.com,
	bp@...en8.de, dvlasenk@...hat.com
Subject: [tip:x86/asm] x86/asm/entry/32: Open-code CLEAR_RREGS

Commit-ID:  ef0cd5dc25404594f832dad9133abae52e3b2fa3
Gitweb:     http://git.kernel.org/tip/ef0cd5dc25404594f832dad9133abae52e3b2fa3
Author:     Denys Vlasenko <dvlasenk@...hat.com>
AuthorDate: Tue, 2 Jun 2015 21:04:01 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 5 Jun 2015 13:22:22 +0200

x86/asm/entry/32: Open-code CLEAR_RREGS

This macro is small, has only four callsites, and one of them is
slightly different using a conditional parameter.

A few saved lines aren't worth the resulting obfuscation.

Generated machine code is identical.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
[ Added comments. ]
Cc: Alexei Starovoitov <ast@...mgrid.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Drewry <wad@...omium.org>
Link: http://lkml.kernel.org/r/1433271842-9139-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/entry/ia32entry.S | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/arch/x86/entry/ia32entry.S b/arch/x86/entry/ia32entry.S
index f00a409..8a45d2c 100644
--- a/arch/x86/entry/ia32entry.S
+++ b/arch/x86/entry/ia32entry.S
@@ -29,15 +29,6 @@
 
 	.section .entry.text, "ax"
 
-	/* clobbers %rax */
-	.macro  CLEAR_RREGS _r9=rax
-	xorl 	%eax,%eax
-	movq	%rax,R11(%rsp)
-	movq	%rax,R10(%rsp)
-	movq	%\_r9,R9(%rsp)
-	movq	%rax,R8(%rsp)
-	.endm
-
 	/*
 	 * Reload arg registers from stack in case ptrace changed them.
 	 * We don't reload %eax because syscall_trace_enter() returned
@@ -243,7 +234,11 @@ sysexit_from_sys_call:
 	TRACE_IRQS_OFF
 	testl %edi, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jz \exit
-	CLEAR_RREGS
+	xorl	%eax, %eax	/* do not leak kernel information */
+	movq	%rax, R11(%rsp)
+	movq	%rax, R10(%rsp)
+	movq	%rax, R9(%rsp)
+	movq	%rax, R8(%rsp)
 	jmp int_with_check
 	.endm
 
@@ -267,7 +262,11 @@ sysenter_tracesys:
 	jz	sysenter_auditsys
 #endif
 	SAVE_EXTRA_REGS
-	CLEAR_RREGS
+	xorl	%eax, %eax	/* do not leak kernel information */
+	movq	%rax, R11(%rsp)
+	movq	%rax, R10(%rsp)
+	movq	%rax, R9(%rsp)
+	movq	%rax, R8(%rsp)
 	movq	%rsp,%rdi        /* &pt_regs -> arg1 */
 	call	syscall_trace_enter
 	LOAD_ARGS32  /* reload args from stack in case ptrace changed it */
@@ -407,7 +406,11 @@ cstar_tracesys:
 #endif
 	xchgl %r9d,%ebp
 	SAVE_EXTRA_REGS
-	CLEAR_RREGS r9
+	xorl	%eax, %eax	/* do not leak kernel information */
+	movq	%rax, R11(%rsp)
+	movq	%rax, R10(%rsp)
+	movq	%r9,  R9(%rsp)
+	movq	%rax, R8(%rsp)
 	movq %rsp,%rdi        /* &pt_regs -> arg1 */
 	call syscall_trace_enter
 	LOAD_ARGS32 1	/* reload args from stack in case ptrace changed it */
@@ -422,7 +425,11 @@ ia32_badarg:
 	jmp ia32_sysret
 
 ia32_ret_from_sys_call:
-	CLEAR_RREGS
+	xorl	%eax, %eax	/* do not leak kernel information */
+	movq	%rax, R11(%rsp)
+	movq	%rax, R10(%rsp)
+	movq	%rax, R9(%rsp)
+	movq	%rax, R8(%rsp)
 	jmp int_ret_from_sys_call
 
 /*
--
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