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 <b...@suse.de> > Cc: Andy Lutomirski <l...@kernel.org> > Cc: Dave Hansen <dave.han...@linux.intel.com> > Cc: Adam Buchbinder <adam.buchbin...@gmail.com> > Cc: Colin Ian King <colin.k...@canonical.com> > Cc: Lorenzo Stoakes <lstoa...@gmail.com> > Cc: Qiaowei Ren <qiaowei....@intel.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Nathan Howard <liverl...@gmail.com> > Cc: Adan Hawthorn <adanhawth...@gmail.com> > Cc: Joe Perches <j...@perches.com> > Cc: Ravi V. Shankar <ravi.v.shan...@intel.com> > Cc: x...@kernel.org > Signed-off-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com> > --- > 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html