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@suse.de Cc: Andy Lutomirski luto@kernel.org 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: Peter Zijlstra peterz@infradead.org Cc: Nathan Howard liverlint@gmail.com Cc: Adan Hawthorn adanhawthorn@gmail.com Cc: Joe Perches joe@perches.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 | 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;