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 such SIB byte points to R/EBP (i.e., base = 5), an explicit displacement is needed. This is, the mod part of the ModRM byte cannot be zero. In case that no displacement is needed, the mod part of the ModRM byte must be 1 with the displacement byte equal to zero.
Make the address decoder to return -EINVAL in the aforementioned case.
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: 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/mm/mpx.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 9d15f6b..c59a851 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -120,6 +120,14 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
case REG_TYPE_BASE: regno = X86_SIB_BASE(insn->sib.value); + /* + * If R/EBP (regno = 5) is indicated in the base part of the SIB + * byte, an explicit displacement must be specified. In other + * words, the mod part of the ModRM byte cannot be zero. + */ + if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0) + return -EINVAL; + if (X86_REX_B(insn->rex_prefix.value)) regno += 8; break;