linux-kernel - [PATCH] x86/asm/entry/64: Use a define for an invalid segment

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Date:	Fri, 3 Apr 2015 14:25:28 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Will Drewry <wad@...omium.org>
Subject: [PATCH] x86/asm/entry/64: Use a define for an invalid segment

On Fri, Apr 03, 2015 at 02:05:17PM +0200, Borislav Petkov wrote:
> Let me do a patch.

---
From: Borislav Petkov <bp@...e.de>
Date: Fri, 3 Apr 2015 14:22:00 +0200
Subject: [PATCH] x86/asm/entry/64: Use a define for an invalid segment
 selector

... instead of a naked number, for better readability.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/include/asm/segment.h | 2 ++
 arch/x86/kernel/cpu/common.c   | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index d394899e055c..5a9856eb12ba 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -39,6 +39,8 @@
 /* ... GDT has it cleared */
 #define SEGMENT_GDT		0x0
 
+#define GDT_ENTRY_INVALID_SEG	0
+
 #ifdef CONFIG_X86_32
 /*
  * The layout of the per-CPU GDT under Linux:
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 2c249b57e4b5..a62cf04dac8a 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1223,7 +1223,7 @@ void syscall_init(void)
 	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)ia32_sysenter_target);
 #else
 	wrmsrl(MSR_CSTAR, ignore_sysret);
-	wrmsrl_safe(MSR_IA32_SYSENTER_CS, 0ULL);
+	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
 	wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
 	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL);
 #endif
-- 
2.3.3

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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