android_kernel_oneplus_msm8998/arch/x86/include/asm/barrier.h
Dan Williams 5bfdf36147 x86/spectre_v1: Disable compiler optimizations over array_index_mask_nospec()
commit eab6870fee877258122a042bfd99ee7908c40280 upstream.

Mark Rutland noticed that GCC optimization passes have the potential to elide
necessary invocations of the array_index_mask_nospec() instruction sequence,
so mark the asm() volatile.

Mark explains:

"The volatile will inhibit *some* cases where the compiler could lift the
 array_index_nospec() call out of a branch, e.g. where there are multiple
 invocations of array_index_nospec() with the same arguments:

        if (idx < foo) {
                idx1 = array_idx_nospec(idx, foo)
                do_something(idx1);
        }

        < some other code >

        if (idx < foo) {
                idx2 = array_idx_nospec(idx, foo);
                do_something_else(idx2);
        }

 ... since the compiler can determine that the two invocations yield the same
 result, and reuse the first result (likely the same register as idx was in
 originally) for the second branch, effectively re-writing the above as:

        if (idx < foo) {
                idx = array_idx_nospec(idx, foo);
                do_something(idx);
        }

        < some other code >

        if (idx < foo) {
                do_something_else(idx);
        }

 ... if we don't take the first branch, then speculatively take the second, we
 lose the nospec protection.

 There's more info on volatile asm in the GCC docs:

   https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Volatile
 "

Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: babdde2698d4 ("x86: Implement array_index_mask_nospec")
Link: https://lkml.kernel.org/lkml/152838798950.14521.4893346294059739135.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-07-03 11:21:26 +02:00

122 lines
3 KiB
C

#ifndef _ASM_X86_BARRIER_H
#define _ASM_X86_BARRIER_H
#include <asm/alternative.h>
#include <asm/nops.h>
/*
* Force strict CPU ordering.
* And yes, this is required on UP too when we're talking
* to devices.
*/
#ifdef CONFIG_X86_32
/*
* Some non-Intel clones support out of order store. wmb() ceases to be a
* nop for these.
*/
#define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)
#define rmb() alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)
#define wmb() alternative("lock; addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM)
#else
#define mb() asm volatile("mfence":::"memory")
#define rmb() asm volatile("lfence":::"memory")
#define wmb() asm volatile("sfence" ::: "memory")
#endif
/**
* array_index_mask_nospec() - generate a mask that is ~0UL when the
* bounds check succeeds and 0 otherwise
* @index: array element index
* @size: number of elements in array
*
* Returns:
* 0 - (index < size)
*/
static inline unsigned long array_index_mask_nospec(unsigned long index,
unsigned long size)
{
unsigned long mask;
asm volatile ("cmp %1,%2; sbb %0,%0;"
:"=r" (mask)
:"r"(size),"r" (index)
:"cc");
return mask;
}
/* Override the default implementation from linux/nospec.h. */
#define array_index_mask_nospec array_index_mask_nospec
/* Prevent speculative execution past this barrier. */
#define barrier_nospec() alternative_2("", "mfence", X86_FEATURE_MFENCE_RDTSC, \
"lfence", X86_FEATURE_LFENCE_RDTSC)
#ifdef CONFIG_X86_PPRO_FENCE
#define dma_rmb() rmb()
#else
#define dma_rmb() barrier()
#endif
#define dma_wmb() barrier()
#ifdef CONFIG_SMP
#define smp_mb() mb()
#define smp_rmb() dma_rmb()
#define smp_wmb() barrier()
#define smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0)
#else /* !SMP */
#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0)
#endif /* SMP */
#define read_barrier_depends() do { } while (0)
#define smp_read_barrier_depends() do { } while (0)
#if defined(CONFIG_X86_PPRO_FENCE)
/*
* For this option x86 doesn't have a strong TSO memory
* model and we should fall back to full barriers.
*/
#define smp_store_release(p, v) \
do { \
compiletime_assert_atomic_type(*p); \
smp_mb(); \
WRITE_ONCE(*p, v); \
} while (0)
#define smp_load_acquire(p) \
({ \
typeof(*p) ___p1 = READ_ONCE(*p); \
compiletime_assert_atomic_type(*p); \
smp_mb(); \
___p1; \
})
#else /* regular x86 TSO memory ordering */
#define smp_store_release(p, v) \
do { \
compiletime_assert_atomic_type(*p); \
barrier(); \
WRITE_ONCE(*p, v); \
} while (0)
#define smp_load_acquire(p) \
({ \
typeof(*p) ___p1 = READ_ONCE(*p); \
compiletime_assert_atomic_type(*p); \
barrier(); \
___p1; \
})
#endif
/* Atomic operations are already serializing on x86 */
#define smp_mb__before_atomic() barrier()
#define smp_mb__after_atomic() barrier()
#endif /* _ASM_X86_BARRIER_H */