Messages in this thread Patch in this message | | | Date | Tue, 29 Jun 2010 14:53:50 +0900 | From | Masami Hiramatsu <> | Subject | [PATCH -tip] [BUGFIX] kprobes/x86: Fix kprobes to skip prefixes correctly |
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Fix resume_execution() and is_IF_modifier() to skip x86 instruction prefixes correctly by using x86 instruction attribute.
Without this fix, resume_execution() can't handle instructions which have non-REX prefixes (REX prefixes are skipped). This will cause unexpected kernel panic by hitting bad address when a kprobe hits on two-byte ret (e.g. "repz ret" generated for Athlon/K8 optimization), because it just checks "repz" and can't recognize the "ret" instruction.
These prefixes can be found easily with x86 instruction attribute. This patch introduces skip_prefixes() and uses it in resume_execution() and is_IF_modifier() to skip prefixes.
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com> ---
arch/x86/kernel/kprobes.c | 33 +++++++++++++++++---------------- 1 files changed, 17 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c index 345a4b1..175f85c 100644 --- a/arch/x86/kernel/kprobes.c +++ b/arch/x86/kernel/kprobes.c @@ -126,16 +126,22 @@ static void __kprobes synthesize_reljump(void *from, void *to) }
/* - * Check for the REX prefix which can only exist on X86_64 - * X86_32 always returns 0 + * Skip the prefixes of the instruction. */ -static int __kprobes is_REX_prefix(kprobe_opcode_t *insn) +static kprobe_opcode_t *__kprobes skip_prefixes(kprobe_opcode_t *insn) { + insn_attr_t attr; + + attr = inat_get_opcode_attribute((insn_byte_t)*insn); + while (inat_is_legacy_prefix(attr)) { + insn++; + attr = inat_get_opcode_attribute((insn_byte_t)*insn); + } #ifdef CONFIG_X86_64 - if ((*insn & 0xf0) == 0x40) - return 1; + if (inat_is_rex_prefix(attr)) + insn++; #endif - return 0; + return insn; }
/* @@ -272,6 +278,9 @@ static int __kprobes can_probe(unsigned long paddr) */ static int __kprobes is_IF_modifier(kprobe_opcode_t *insn) { + /* Skip prefixes */ + insn = skip_prefixes(insn); + switch (*insn) { case 0xfa: /* cli */ case 0xfb: /* sti */ @@ -280,13 +289,6 @@ static int __kprobes is_IF_modifier(kprobe_opcode_t *insn) return 1; }
- /* - * on X86_64, 0x40-0x4f are REX prefixes so we need to look - * at the next byte instead.. but of course not recurse infinitely - */ - if (is_REX_prefix(insn)) - return is_IF_modifier(++insn); - return 0; }
@@ -803,9 +805,8 @@ static void __kprobes resume_execution(struct kprobe *p, unsigned long orig_ip = (unsigned long)p->addr; kprobe_opcode_t *insn = p->ainsn.insn;
- /*skip the REX prefix*/ - if (is_REX_prefix(insn)) - insn++; + /* Skip prefixes */ + insn = skip_prefixes(insn);
regs->flags &= ~X86_EFLAGS_TF; switch (*insn) {
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