Re: [PATCH 3.16.y,3.18.y] kprobes/x86: Return correct length in __copy_instruction()

[Luis Henriques <luis.henriques@canonical.com>]

On Tue, May 19, 2015 at 04:58:14PM +0300, Eugene Shatokhin wrote:
> Commit c80e5c0c23ce2282476fdc64c4b5e3d3a40723fd upstream.
> This is the backport of that fix for 3.16.y-3.18.y.
>

Thank you, Eugene.  I'll queue this for the 3.16 kernel.

Cheers,
--
Lu�s

> 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>
> ---
>  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 93d2c04..f2e281c 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -330,13 +330,16 @@ int __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)) {
> @@ -366,7 +369,7 @@ 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)
> -- 
> 2.3.2
> 
> --
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