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    Subject[PATCH 3.12 065/124] kprobes/x86: Return correct length in __copy_instruction()
    Date
    From: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    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: Jiri Slaby <jslaby@suse.cz>
    ---
    arch/x86/kernel/kprobes/core.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
    index a1f5b1866cbe..490fee15fea5 100644
    --- a/arch/x86/kernel/kprobes/core.c
    +++ b/arch/x86/kernel/kprobes/core.c
    @@ -326,13 +326,16 @@ int __kprobes __copy_instruction(u8 *dest, u8 *src)
    {
    struct insn insn;
    kprobe_opcode_t buf[MAX_INSN_SIZE];
    + int length;

    kernel_insn_init(&insn, (void *)recover_probed_instruction(buf, (unsigned long)src));
    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)) {
    @@ -362,7 +365,7 @@ int __kprobes __copy_instruction(u8 *dest, u8 *src)
    *(s32 *) disp = (s32) newdisp;
    }
    #endif
    - return insn.length;
    + return length;
    }

    static int __kprobes arch_copy_kprobe(struct kprobe *p)
    --
    2.4.6


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