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From: tip-bot for Masami Hiramatsu on 29 Jun 2010 05:30
Commit-ID: 567a9fd86735ccdc897768ed2dacdd5e83a13509
Gitweb: http://git.kernel.org/tip/567a9fd86735ccdc897768ed2dacdd5e83a13509
Author: Masami Hiramatsu <masami.hiramatsu.pt(a)hitachi.com>
AuthorDate: Tue, 29 Jun 2010 14:53:50 +0900
Committer: Ingo Molnar <mingo(a)elte.hu>
CommitDate: Tue, 29 Jun 2010 10:43:41 +0200

kprobes/x86: Fix kprobes to skip prefixes correctly

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(a)hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth(a)in.ibm.com>
LKML-Reference: <4C298A6E.8070609(a)hitachi.com>
Signed-off-by: Ingo Molnar <mingo(a)elte.hu>
---
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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Prev: x86, alternatives: Use 16-bit numbers for cpufeature index
Next: [tip:perf/core] tracing: Remove redundant raw_init callbacks