[PATCH -tip ] kprobes/x86: Return correct length in __copy_instruction()

From: Masami Hiramatsu
Date: Tue Mar 17 2015 - 06:10:42 EST

From: Eugene Shatokhin <eugene.shatokhin@xxxxxxxxxx>

On x86-64, __copy_instruction() always returns 0 (error) if the
instruction uses %rip-relative addressing. This is because
kernel_insn_init() is called the second time for 'insn' instance
in such cases and sets all its fields to 0.

Because of this, trying to place a Kprobe on such instruction will
fail, register_kprobe() will return -EINVAL.

This patch fixes the problem.

Signed-off-by: Eugene Shatokhin <eugene.shatokhin@xxxxxxxxxx>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
arch/x86/kernel/kprobes/core.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 4e3d5a9..03189d8 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -354,6 +354,7 @@ int __copy_instruction(u8 *dest, u8 *src)
struct insn insn;
kprobe_opcode_t buf[MAX_INSN_SIZE];
+ int length;
unsigned long recovered_insn =
recover_probed_instruction(buf, (unsigned long)src);

@@ -361,16 +362,18 @@ int __copy_instruction(u8 *dest, u8 *src)
return 0;
kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
+ length = insn.length;
/* Another subsystem puts a breakpoint, failed to recover */
if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
return 0;
- memcpy(dest, insn.kaddr, insn.length);
+ memcpy(dest, insn.kaddr, length);

#ifdef CONFIG_X86_64
if (insn_rip_relative(&insn)) {
s64 newdisp;
u8 *disp;
- kernel_insn_init(&insn, dest, insn.length);
+ kernel_insn_init(&insn, dest, length);
* The copied instruction uses the %rip-relative addressing
@@ -394,7 +397,7 @@ int __copy_instruction(u8 *dest, u8 *src)
*(s32 *) disp = (s32) newdisp;
- return insn.length;
+ return length;

static int arch_copy_kprobe(struct kprobe *p)

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