On Tue, Mar 07, 2017 at 04:32:43PM -0800, Ricardo Neri wrote:
Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when the mod part of the ModRM byte is zero and R/EBP is specified in the R/M part of such bit, the value of the aforementioned register should not be used in the address computation. Instead, a 32-bit displacement is expected. The instruction decoder takes care of setting the displacement to the expected value. Returning -EDOM signals callers that they should ignore the value of such register when computing the address encoded in the instruction operands.
Also, callers should exercise care to correctly interpret this particular case. In IA-32e 64-bit mode, the address is given by the displacement plus the value of the RIP. In IA-32e compatibility mode, the value of EIP is ignored. This correction is done for our insn_get_addr_ref.
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 | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index cda6c71..ea10b03 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -250,6 +250,14 @@ 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);
/* if mod=0, register R/EBP is not used in the address* computation. Instead, a 32-bit displacement is expected;* the instruction decoder takes care of reading such* displacement. This is true for both R/EBP and R13, as the* REX.B bit is not decoded.*/
I'd simply write here: "ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit displacement is following."
In addition, kernel comments style is:
/* * A sentence ending with a full-stop. * Another sentence. ... * More sentences. ... */
if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)return -EDOM;
if (X86_MODRM_MOD(insn->modrm.value) == 0 && X86_MODRM_RM(insn->modrm.value) == 5)
looks more understandable to me.
if (X86_REX_B(insn->rex_prefix.value)) regno += 8; break;@@ -599,9 +607,22 @@ 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.* The only case in which we see this value is when* R/M points to R/EBP. In such a case, in 64-bit mode* the effective address is relative to tho RIP.
s/tho//
*/
Kernel comments style is:
/* * A sentence ending with a full-stop. * Another sentence. ... * More sentences. ... */
if (addr_offset == -EDOM) {eff_addr = 0;+#ifdef CONFIG_X86_64
if (user_64bit_mode(regs))eff_addr = (long)regs->ip;
Is regs->ip the rIP of the *following* insn?
+#endif
You can do this in a prepatch and then get rid of the ifdeffery here:
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index 2b5d686ea9f3..f6239273c5f1 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -115,9 +115,9 @@ static inline int v8086_mode(struct pt_regs *regs) #endif }
-#ifdef CONFIG_X86_64 static inline bool user_64bit_mode(struct pt_regs *regs) { +#ifdef CONFIG_X86_64 #ifndef CONFIG_PARAVIRT /* * On non-paravirt systems, this is the only long mode CPL 3 @@ -128,6 +128,9 @@ static inline bool user_64bit_mode(struct pt_regs *regs) /* Headers are too twisted for this to go in paravirt.h. */ return regs->cs == __USER_CS || regs->cs == pv_info.extra_user_64bit_cs; #endif +#else /* !CONFIG_X86_64 */ + return false; +#endif }
#define current_user_stack_pointer() current_pt_regs()->sp ---