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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>
This commit is contained in:
Masami Hiramatsu 2010-06-29 14:53:50 +09:00 committed by Ingo Molnar
parent a1d0ce8213
commit 567a9fd867
1 changed files with 17 additions and 16 deletions
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33
arch/x86/kernel/kprobes.c
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@ -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) {