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

[Ricardo Neri <ricardo.neri-calderon@linux.intel.com>]

On Fri, 2017-09-08 at 15:57 +0200, Borislav Petkov wrote:
> 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@linux.intel.com>
> > Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
> > Cc: Colin Ian King <colin.king@canonical.com>
> > Cc: Lorenzo Stoakes <lstoakes@gmail.com>
> > Cc: Qiaowei Ren <qiaowei.ren@intel.com>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Cc: Masami Hiramatsu <mhiramat@kernel.org>
> > Cc: Adrian Hunter <adrian.hunter@intel.com>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Thomas Garnier <thgarnie@google.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Borislav Petkov <bp@suse.de>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
> > Cc: x86@kernel.org
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> > ---
> >  arch/x86/lib/insn-eval.c | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> Reviewed-by: Borislav Petkov <bp@suse.de>

Thanks for your review!

BR,
Ricardo