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

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(2015/03/09 20:19), Eugene Shatokhin wrote:
> 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.

Oops, good catch!

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Thank you!

> 
> This patch fixes the problem.
> 
> Signed-off-by: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>
> ---
>  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);
>  	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)
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com