Messages in this thread Patch in this message | | | From | Ricardo Neri <> | Subject | [PATCH v7 14/26] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 5 | Date | Fri, 5 May 2017 11:17:12 -0700 |
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Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when ModRM.mod is zero and ModRM.rm is 101b, a 32-bit displacement follows the ModRM byte. This means that none of the registers are used in the computation of the effective address. A return value of -EDOM signals callers that they should not use the value of registers when computing the effective address for the instruction.
In IA-32e 64-bit mode (long mode), the effective address is given by the 32-bit displacement plus the value of RIP of the next instruction. In IA-32e compatibility mode (protected mode), only the displacement is used.
The instruction decoder takes care of obtaining the displacement.
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: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Kees Cook <keescook@chromium.org> Cc: Thomas Garnier <thgarnie@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Borislav Petkov <bp@suse.de> Cc: Dmitry Vyukov <dvyukov@google.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/lib/insn-eval.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 693e5a8..4f600de 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -379,6 +379,12 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, switch (type) { case REG_TYPE_RM: regno = X86_MODRM_RM(insn->modrm.value); + /* + * ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit displacement + * follows the ModRM byte. + */ + if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5) + return -EDOM; if (X86_REX_B(insn->rex_prefix.value)) regno += 8; break; @@ -730,9 +736,21 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); - if (addr_offset < 0) + /* + * -EDOM means that we must ignore the address_offset. + * In such a case, in 64-bit mode the effective address + * relative to the RIP of the following instruction. + */ + if (addr_offset == -EDOM) { + eff_addr = 0; + if (user_64bit_mode(regs)) + eff_addr = (long)regs->ip + + insn->length; + } else if (addr_offset < 0) { goto out_err; - eff_addr = regs_get_register(regs, addr_offset); + } else { + eff_addr = regs_get_register(regs, addr_offset); + } } eff_addr += insn->displacement.value; } -- 2.9.3
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