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

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 2af4ccd..3a463f9 100644 (file)
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -550,11 +550,6 @@ 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