Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that if a SIB byte is used and SIB.base is 101b and ModRM.mod is zero, then the base part of the base part of the effective address computation is null. To signal this situation, a -EDOM error is returned to indicate callers to ignore the base value present in the register operand.
In this scenario, a 32-bit displacement follows the SIB byte. Displacement is obtained when the instruction decoder parses the operands. Cc: Borislav Petkov <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Adam Buchbinder <[email protected]> Cc: Colin Ian King <[email protected]> Cc: Lorenzo Stoakes <[email protected]> Cc: Qiaowei Ren <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Nathan Howard <[email protected]> Cc: Adan Hawthorn <[email protected]> Cc: Joe Perches <[email protected]> Cc: Ravi V. Shankar <[email protected]> Cc: [email protected] Signed-off-by: Ricardo Neri <[email protected]> --- arch/x86/mm/mpx.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 892aa6468805..53e24ca01f29 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -123,6 +123,14 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, case REG_TYPE_BASE: regno = X86_SIB_BASE(insn->sib.value); + /* + * If ModRM.mod is 0 and SIB.base == 5, the base of the + * register-indirect addressing is 0. 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; @@ -164,17 +172,21 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) eff_addr = regs_get_register(regs, addr_offset); } else { if (insn->sib.nbytes) { + /* + * Negative values in the base and index offset means + * an error when decoding the SIB byte. Except -EDOM, + * which means that the registers should not be used + * in the address computation. + */ base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); - if (base_offset < 0) + if (base_offset == -EDOM) + base = 0; + else if (base_offset < 0) goto out_err; + else + base = regs_get_register(regs, base_offset); indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); - - /* - * A negative offset generally means a error, except - * -EDOM, which means that the contents of the register - * should not be used as index. - */ if (indx_offset == -EDOM) indx = 0; else if (indx_offset < 0) @@ -182,8 +194,6 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) else indx = regs_get_register(regs, indx_offset); - base = regs_get_register(regs, base_offset); - eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); -- 2.13.0
