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From: tip-bot for Andy Lutomirski <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
	tglx@linutronix.de, luto@amacapital.net, hpa@zytor.com
Subject: [tip:x86/urgent] x86, tls, ldt: Stop checking lm in LDT_empty
Date: Thu, 22 Jan 2015 12:13:42 -0800	[thread overview]
Message-ID: <tip-e30ab185c490e9a9381385529e0fd32f0a399495@git.kernel.org> (raw)
In-Reply-To: <72a059de55e86ad5e2935c80aa91880ddf19d07c.1421954363.git.luto@amacapital.net>

Commit-ID:  e30ab185c490e9a9381385529e0fd32f0a399495
Gitweb:     http://git.kernel.org/tip/e30ab185c490e9a9381385529e0fd32f0a399495
Author:     Andy Lutomirski <luto@amacapital.net>
AuthorDate: Thu, 22 Jan 2015 11:27:58 -0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 22 Jan 2015 21:11:06 +0100

x86, tls, ldt: Stop checking lm in LDT_empty

32-bit programs don't have an lm bit in their ABI, so they can't
reliably cause LDT_empty to return true without resorting to memset.
They shouldn't need to do this.

This should fix a longstanding, if minor, issue in all 64-bit kernels
as well as a potential regression in the TLS hardening code.

Fixes: 41bdc78544b8 x86/tls: Validate TLS entries to protect espfix
Cc: stable@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: torvalds@linux-foundation.org
Link: http://lkml.kernel.org/r/72a059de55e86ad5e2935c80aa91880ddf19d07c.1421954363.git.luto@amacapital.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/desc.h | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index 50d033a..fc237fd 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -251,7 +251,8 @@ static inline void native_load_tls(struct thread_struct *t, unsigned int cpu)
 		gdt[GDT_ENTRY_TLS_MIN + i] = t->tls_array[i];
 }
 
-#define _LDT_empty(info)				\
+/* This intentionally ignores lm, since 32-bit apps don't have that field. */
+#define LDT_empty(info)					\
 	((info)->base_addr		== 0	&&	\
 	 (info)->limit			== 0	&&	\
 	 (info)->contents		== 0	&&	\
@@ -261,12 +262,6 @@ static inline void native_load_tls(struct thread_struct *t, unsigned int cpu)
 	 (info)->seg_not_present	== 1	&&	\
 	 (info)->useable		== 0)
 
-#ifdef CONFIG_X86_64
-#define LDT_empty(info) (_LDT_empty(info) && ((info)->lm == 0))
-#else
-#define LDT_empty(info) (_LDT_empty(info))
-#endif
-
 static inline void clear_LDT(void)
 {
 	set_ldt(NULL, 0);

  reply	other threads:[~2015-01-22 20:13 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-22 19:27 [PATCH 0/2] x86: TLS regression fixes Andy Lutomirski
2015-01-22 19:27 ` [PATCH 1/2] x86, tls, ldt: Stop checking lm in LDT_empty Andy Lutomirski
2015-01-22 20:13   ` tip-bot for Andy Lutomirski [this message]
2015-01-22 19:27 ` [PATCH 2/2] x86, tls: Interpret an all-zero struct user_desc as "no segment" Andy Lutomirski
2015-01-22 19:47   ` Borislav Petkov
2015-01-22 20:12     ` Andy Lutomirski
2015-01-22 20:14   ` [tip:x86/urgent] x86, tls: Interpret an all-zero struct user_desc as %22no segment%22 tip-bot for Andy Lutomirski
2015-01-22 20:54   ` [tip:x86/urgent] x86, tls: Interpret an all-zero struct user_desc as "no segment" tip-bot for Andy Lutomirski
2015-01-22 19:56 ` [PATCH 0/2] x86: TLS regression fixes Linus Torvalds

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