Re: [PATCH v8 11/28] x86/insn-eval: Add utility function to identify string instructions

From: Borislav Petkov
Date: Fri Sep 08 2017 - 12:14:33 EST

On Fri, Aug 18, 2017 at 05:27:52PM -0700, Ricardo Neri wrote:
> String instructions are special because, in protected mode, the linear
> address is always obtained via the ES segment register in operands that
> use the (E)DI register; the DS segment register in operands that use
> the (E)SI register. Furthermore, segment override prefixes are ignored
> when calculating a linear address involving the (E)DI register; segment
> override prefixes can be used when calculating linear addresses involving
> the (E)SI register.
> It follows that linear addresses are calculated differently for the case of
> string instructions. The purpose of this utility function is to identify
> such instructions for callers to determine a linear address correctly.
> Note that this function only identifies string instructions; it does not
> determine what segment register to use in the address computation. That is
> left to callers. A subsequent commmit introduces a function to determine
> the segment register to use given the instruction, operands and
> segment override prefixes.
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Adam Buchbinder <adam.buchbinder@xxxxxxxxx>
> Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> Cc: Qiaowei Ren <>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Thomas Garnier <thgarnie@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> ---
> arch/x86/lib/insn-eval.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)

Reviewed-by: Borislav Petkov <bp@xxxxxxx>


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