linux-kernel - [tip:x86/espfix] x86-32, espfix: Remove filter for espfix32 due to race

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Date:	Wed, 30 Apr 2014 14:19:10 -0700
From:	"tip-bot for H. Peter Anvin" <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	tglx@...utronix.de, hpa@...ux.intel.com
Subject: [tip:x86/espfix] x86-32, espfix:
  Remove filter for espfix32 due to race

Commit-ID:  246f2d2ee1d715e1077fc47d61c394569c8ee692
Gitweb:     http://git.kernel.org/tip/246f2d2ee1d715e1077fc47d61c394569c8ee692
Author:     H. Peter Anvin <hpa@...ux.intel.com>
AuthorDate: Wed, 30 Apr 2014 14:03:25 -0700
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Wed, 30 Apr 2014 14:14:49 -0700

x86-32, espfix: Remove filter for espfix32 due to race

It is not safe to use LAR to filter when to go down the espfix path,
because the LDT is per-process (rather than per-thread) and another
thread might change the descriptors behind our back.  Fortunately it
is always *safe* (if a bit slow) to go down the espfix path, and a
32-bit LDT stack segment is extremely rare.

Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Link: http://lkml.kernel.org/r/1398816946-3351-1-git-send-email-hpa@linux.intel.com
Cc: <stable@...r.kernel.org> # consider after upstream merge
---
 arch/x86/kernel/entry_32.S | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index a2a4f46..2780b8f 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -551,11 +551,6 @@ ENTRY(iret_exc)
 
 	CFI_RESTORE_STATE
 ldt_ss:
-	larl PT_OLDSS(%esp), %eax
-	jnz restore_nocheck
-	testl $0x00400000, %eax		# returning to 32bit stack?
-	jnz restore_nocheck		# allright, normal return
-
 #ifdef CONFIG_PARAVIRT
 	/*
 	 * The kernel can't run on a non-flat stack if paravirt mode
--
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