Re: [PATCH v9 17/29] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 101b

Borislav Petkov
2017-10-20T15:45:04Z

On Tue, Oct 03, 2017 at 08:54:20PM -0700, Ricardo Neri wrote:
> Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software
> Developer's Manual volume 2A states that when ModRM.mod is zero and
> ModRM.rm is 101b, a 32-bit displacement follows the ModRM byte. This means
> that none of the registers are used in the computation of the effective
> address. A return value of -EDOM indicates callers that they should not
> use the value of registers when computing the effective address for the
> instruction.
>
> In long mode, the effective address is given by the 32-bit displacement
> plus the location of the next instruction. In protected mode, only the
> displacement is used.
>
> The instruction decoder takes care of obtaining the displacement.
>
> 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 | 25 ++++++++++++++++++++++---
> 1 file changed, 22 insertions(+), 3 deletions(-)

Reviewed-by: Borislav Petkov <bp@suse.de>

--
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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