kprobes/x86: Return correct length in __copy_instruction()

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>

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 4e3d5a9621fe0052fac43d5ad6c109b9d3f54447..03189d86357d9253aff5d064e4a893e24091f00c 100644 (file)
--- 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)