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x86, tls, ldt: Stop checking lm in LDT_empty 

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: 41bdc78544 x86/tls: Validate TLS entries to protect espfix
Cc: stable@vger.kernel.org
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>
This commit is contained in:
Andy Lutomirski 2015-01-22 11:27:58 -08:00 committed by Thomas Gleixner
parent e9d1b4f3c6
commit e30ab185c4
1 changed files with 2 additions and 7 deletions
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9
arch/x86/include/asm/desc.h
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@ -251,7 +251,8 @@ static inline void native_load_tls(struct thread_struct *t, unsigned int cpu)
gdt[GDT_ENTRY_TLS_MIN + i] = t->tls_array[i]; 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)->base_addr == 0 && \
(info)->limit == 0 && \ (info)->limit == 0 && \
(info)->contents == 0 && \ (info)->contents == 0 && \
@ -261,12 +262,6 @@ static inline void native_load_tls(struct thread_struct *t, unsigned int cpu)
(info)->seg_not_present == 1 && \ (info)->seg_not_present == 1 && \
(info)->useable == 0) (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) static inline void clear_LDT(void)
{ {
set_ldt(NULL, 0); set_ldt(NULL, 0);