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[3.11,012/198] x86-32, espfix: Remove filter for espfix32 due to race

Message ID 1404379241-8590-13-git-send-email-luis.henriques@canonical.com
State New
Headers show

Commit Message

Luis Henriques July 3, 2014, 9:17 a.m. UTC 
3.11.10.13 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "H. Peter Anvin" <hpa@linux.intel.com>

commit 246f2d2ee1d715e1077fc47d61c394569c8ee692 upstream.

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@linux.intel.com>
Link: http://lkml.kernel.org/r/1398816946-3351-1-git-send-email-hpa@linux.intel.com
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 arch/x86/kernel/entry_32.S | 5 -----
 1 file changed, 5 deletions(-)
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Patch

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index bbc89cf397bd..473f125a3a52 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -554,11 +554,6 @@  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