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Commit babdde26 authored by Dan Williams's avatar Dan Williams Committed by Thomas Gleixner
Browse files

x86: Implement array_index_mask_nospec 



array_index_nospec() uses a mask to sanitize user controllable array
indexes, i.e. generate a 0 mask if 'index' >= 'size', and a ~0 mask
otherwise. While the default array_index_mask_nospec() handles the
carry-bit from the (index - size) result in software.

The x86 array_index_mask_nospec() does the same, but the carry-bit is
handled in the processor CF flag without conditional instructions in the
control flow.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
Cc: gregkh@linuxfoundation.org
Cc: alan@linux.intel.com
Link: https://lkml.kernel.org/r/151727414808.33451.1873237130672785331.stgit@dwillia2-desk3.amr.corp.intel.com
parent f3804203

arch/x86/include/asm/barrier.h

+24 −0
Original line number Diff line number Diff line
@@ -24,6 +24,30 @@ 
#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 ("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



#ifdef CONFIG_X86_PPRO_FENCE

#define dma_rmb()	rmb()

#else