linux-kernel - Re: [PATCH v2 3.16] x86,kprobes: Don't try to resolve kprobe faults from userspace

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Date:	Mon, 14 Jul 2014 07:39:02 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 3.16] x86,kprobes: Don't try to resolve kprobe faults
 from userspace

(2014/07/12 2:27), Andy Lutomirski wrote:
> This commit:
> 
>     commit 6f6343f53d133bae516caf3d254bce37d8774625
>     Author: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>     Date:   Thu Apr 17 17:17:33 2014 +0900
> 
>         kprobes/x86: Call exception handlers directly from do_int3/do_debug
> 
> appears to have inadvertently dropped a check that the int3 came
> from kernel mode.  Trying to dereference addr when addr is
> user-controlled is completely bogus.

Oops, right!

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

Thank you very much!

> 
> Signed-off-by: Andy Lutomirski <luto@...capital.net>
> ---
> 
> Changes from v1: Fixed the changelog message
> 
>  arch/x86/kernel/kprobes/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 7596df6..67e6d19 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -574,6 +574,9 @@ int kprobe_int3_handler(struct pt_regs *regs)
>  	struct kprobe *p;
>  	struct kprobe_ctlblk *kcb;
>  
> +	if (user_mode_vm(regs))
> +		return 0;
> +
>  	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
>  	/*
>  	 * We don't want to be preempted for the entire
> 


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


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