linux-kernel - [PATCH 4/9] x86/asm/entry/64: delay popping return address in stubs

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Date:	Thu,  2 Apr 2015 16:36:13 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/9] x86/asm/entry/64: delay popping return address in stubs

This allows to remove "addq $8, %rsp" from five of six execve and sigreturn stubs.

More importantly, it enables next optimization: faster return on execve failure.

Run-tested.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Borislav Petkov <bp@...en8.de>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Alexei Starovoitov <ast@...mgrid.com>
CC: Will Drewry <wad@...omium.org>
CC: Kees Cook <keescook@...omium.org>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/entry_64.S | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 1cf245d..060cb2e 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -418,11 +418,11 @@ END(stub_\func)
 
 ENTRY(stub_execve)
 	CFI_STARTPROC
-	addq $8, %rsp
-	DEFAULT_FRAME 0
-	SAVE_EXTRA_REGS
+	DEFAULT_FRAME 0, 8
+	SAVE_EXTRA_REGS 8
 	call sys_execve
 return_from_stub:
+	addq $8, %rsp
 	movq %rax,RAX(%rsp)
 	RESTORE_EXTRA_REGS
 	jmp int_ret_from_sys_call
@@ -431,9 +431,8 @@ END(stub_execve)
 
 ENTRY(stub_execveat)
 	CFI_STARTPROC
-	addq $8, %rsp
-	DEFAULT_FRAME 0
-	SAVE_EXTRA_REGS
+	DEFAULT_FRAME 0, 8
+	SAVE_EXTRA_REGS 8
 	call sys_execveat
 	jmp  return_from_stub
 	CFI_ENDPROC
@@ -445,8 +444,7 @@ END(stub_execveat)
  */
 ENTRY(stub_rt_sigreturn)
 	CFI_STARTPROC
-	addq $8, %rsp
-	DEFAULT_FRAME 0
+	DEFAULT_FRAME 0, 8
 	/*
 	 * Despite RESTORE_EXTRA_REGS in return_from_stub,
 	 * no need to SAVE_EXTRA_REGS here:
@@ -461,8 +459,7 @@ END(stub_rt_sigreturn)
 #ifdef CONFIG_X86_X32_ABI
 ENTRY(stub_x32_rt_sigreturn)
 	CFI_STARTPROC
-	addq $8, %rsp
-	DEFAULT_FRAME 0
+	DEFAULT_FRAME 0, 8
 	/* No need to SAVE_EXTRA_REGS */
 	call sys32_x32_rt_sigreturn
 	jmp  return_from_stub
@@ -471,9 +468,8 @@ END(stub_x32_rt_sigreturn)
 
 ENTRY(stub_x32_execve)
 	CFI_STARTPROC
-	addq $8, %rsp
-	DEFAULT_FRAME 0
-	SAVE_EXTRA_REGS
+	DEFAULT_FRAME 0, 8
+	SAVE_EXTRA_REGS 8
 	call compat_sys_execve
 	jmp  return_from_stub
 	CFI_ENDPROC
@@ -481,9 +477,8 @@ END(stub_x32_execve)
 
 ENTRY(stub_x32_execveat)
 	CFI_STARTPROC
-	addq $8, %rsp
-	DEFAULT_FRAME 0
-	SAVE_EXTRA_REGS
+	DEFAULT_FRAME 0, 8
+	SAVE_EXTRA_REGS 8
 	call compat_sys_execveat
 	jmp  return_from_stub
 	CFI_ENDPROC
-- 
1.8.1.4

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