[PATCH 4.0 19/22] kprobes/x86: Return correct length in __copy_instruction()

Greg Kroah-Hartman
2015-06-27T01:16:53Z

From: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>

commit c80e5c0c23ce2282476fdc64c4b5e3d3a40723fd upstream.

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@rosalab.ru>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Link: http://lkml.kernel.org/r/20150317100918.28349.94654.stgit@localhost.localdomain
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kernel/kprobes/core.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- 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);
insn_get_length(&insn);
+ 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);
insn_get_displacement(&insn);
/*
* The copied instruction uses the %rip-relative addressing
@@ -394,7 +397,7 @@ int __copy_instruction(u8 *dest, u8 *src
*(s32 *) disp = (s32) newdisp;
}
#endif
- return insn.length;
+ return length;
}

static int arch_copy_kprobe(struct kprobe *p)