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Subject[PATCH 3.2 124/152] x86, tls, ldt: Stop checking lm in LDT_empty
3.2.67-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Andy Lutomirski <luto@amacapital.net>

commit e30ab185c490e9a9381385529e0fd32f0a399495 upstream.

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
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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/x86/include/asm/desc.h | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)

--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -248,7 +248,8 @@ static inline void native_load_tls(struc
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 && \
@@ -258,12 +259,6 @@ static inline void native_load_tls(struc
(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);


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