4.15-stable review patch. If anyone has any objections, please let me know.
------------------ From: Dan Williams [email protected] commit babdde2698d482b6c0de1eab4f697cf5856c5859 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: Linus Torvalds <[email protected]> Signed-off-by: Dan Williams <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Link: https://lkml.kernel.org/r/151727414808.33451.1873237130672785331.st...@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Greg Kroah-Hartman <[email protected]> --- arch/x86/include/asm/barrier.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -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
