linux-kernel - Re: Is it really correct to check for breakpoint in kernel space against ptracer's address space?

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Message-ID: <CALCETrVC26_hQjKFCfum2jBkxScyCun6PQc=UGmVwavR7jOaFg@mail.gmail.com>
Date:	Tue, 10 May 2016 09:10:19 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ruslan Kabatsayev <b7.10110111@...il.com>
Cc:	Andy Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Is it really correct to check for breakpoint in kernel space
 against ptracer's address space?

On Tue, May 10, 2016 at 8:40 AM, Ruslan Kabatsayev
<b7.10110111@...il.com> wrote:
> On Tue, May 10, 2016 at 6:23 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> Anyway, what kernel are you on?  I think I fixed your specific issue in:
>>
>> commit 27747f8bc355a2808ca9e490ab6866acd85b4c16
>> Author: Andy Lutomirski <luto@...nel.org>
>> Date:   Thu Jul 30 20:32:42 2015 -0700
>>
>>     perf/x86/hw_breakpoints: Fix check for kernel-space breakpoints
>>
>> If that does fix it and it's a problem for you on older kernels, you
>> could ask for a backport.
>
> Indeed, I was using a 3.12 kernel. This should indeed fix it, thanks.
>
> BTW, in that commit, why isn't va>=TASK_SIZE_MAX redundant with the
> second operand of ||? If va is aligned to a multiple of len (so
> va+len-1 doesn't overflow), then in what cases would the first
> condition be true with the second being false?

An excellent question :)

I think that, when I wrote that, I wasn't 100% convinced that len
couldn't be zero.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC