linux-kernel - [PATCH 3/5] x86/asm/entry/32: Jump from SYSENTER32 to SYSCALL32 code path

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Date:	Mon, 27 Jul 2015 22:33:46 +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>,
	"Krzysztof A. Sobiecki" <sobkas@...il.com>,
	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 3/5] x86/asm/entry/32: Jump from SYSENTER32 to SYSCALL32 code path

In 32-bit SYSENTER code, load arg6 into R9 instead of EBP.
Jump to SYSCALL code path after we finish setting up pt_regs
and clearing FLAGS_NT.

This leaves most of SYSENTER32 code path inaccessible.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Ingo Molnar <mingo@...nel.org>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Krzysztof A. Sobiecki <sobkas@...il.com>
CC: Steven Rostedt <rostedt@...dmis.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/entry/entry_64_compat.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index df102e8..d74745a 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -93,7 +93,7 @@ ENTRY(entry_SYSENTER_compat)
 	 * 32-bit zero extended
 	 */
 	ASM_STAC
-1:	movl	(%rbp), %ebp
+1:	movl	(%rbp), %r9d
 	_ASM_EXTABLE(1b, ia32_badarg)
 	ASM_CLAC
 
@@ -105,6 +105,7 @@ ENTRY(entry_SYSENTER_compat)
 	testl	$X86_EFLAGS_NT, EFLAGS(%rsp)
 	jnz	sysenter_fix_flags
 sysenter_flags_fixed:
+	jmp	sysenter_jumps_here
 
 	orl	$TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl	$_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -343,6 +344,7 @@ ENTRY(entry_SYSCALL_compat)
 	_ASM_EXTABLE(1b, ia32_badarg)
 	ASM_CLAC
 
+sysenter_jumps_here:
 	orl	$TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl	$_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jnz	cstar_tracesys
-- 
1.8.1.4

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