Commit 567a9fd8 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Ingo Molnar
Browse files

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: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
LKML-Reference: <4C298A6E.8070609@hitachi.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent a1d0ce82

arch/x86/kernel/kprobes.c

+17 −16
Original line number Diff line number Diff line
@@ -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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