On Mon, 2017-05-29 at 15:07 +0200, Borislav Petkov wrote: > 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." Agreed. I will update the comment to make more sense. Thanks and BR, Ricardo -- 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
