On Fri, May 05, 2017 at 11:17:03AM -0700, Ricardo Neri wrote:
> Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software
> Developer's Manual volume 2A states that when a SIB byte is used and the
> base of the SIB byte points is base = 101b and the mod part
> of the ModRM byte is zero, the base port on the effective address
> computation is null. In this case, a 32-bit displacement follows the SIB
> byte. This is obtained when the instruction decoder parses the operands.
>
> To signal this scenario, a -EDOM error is returned to indicate callers that
> they should ignore the base.
>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> 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 <qiaowei.ren@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Nathan Howard <liverlint@xxxxxxxxx>
> Cc: Adan Hawthorn <adanhawthorn@xxxxxxxxx>
> Cc: Joe Perches <joe@xxxxxxxxxxx>
> Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> ---
> arch/x86/mm/mpx.c | 27 ++++++++++++++++++++-------
> 1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
> index 7397b81..30aef92 100644
> --- a/arch/x86/mm/mpx.c
> +++ b/arch/x86/mm/mpx.c
> @@ -122,6 +122,15 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
>
> case REG_TYPE_BASE:
> regno = X86_SIB_BASE(insn->sib.value);
> + /*
> + * If ModRM.mod is 0 and SIB.base == 5, the base of the
> + * register-indirect addressing is 0. In this case, a
> + * 32-bit displacement is expected in this case; the
> + * instruction decoder finds such displacement for us.
That last sentence reads funny. Just say:
"In this case, a 32-bit displacement follows the SIB byte."
> + */
> + if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5)
> + return -EDOM;
> +
> if (X86_REX_B(insn->rex_prefix.value))
> regno += 8;
> break;
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
--
To unsubscribe from this list: send the line "unsubscribe linux-msdos" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
