From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Date: Tue, 29 Jun 2010 05:53:50 +0000 (+0900)

Subject: kprobes/x86: Fix kprobes to skip prefixes correctly

X-Git-Tag: v2.6.36-rc1~41^2~53

X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=567a9fd86735ccdc897768ed2dacdd5e83a13509

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@hitachi.com>

Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

LKML-Reference: <4C298A6E.8070609@hitachi.com>

Signed-off-by: Ingo Molnar <mingo@elte.hu>

---

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) {