[PATCH 3.12 158/181] x86-32, espfix: Remove filter for espfix32 due to race

Jiri Slaby
2014-06-30T12:46:47Z

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

3.12-stable review patch. If anyone has any objections, please let me know.

===============

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: Jiri Slaby <jslaby@suse.cz>
---
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 15a569a47b4d..cef8f5132b87 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
--
2.0.0