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From: Laura Abbott <labbott@redhat.com>
Message-ID: <37807af6-1743-059c-614a-1328c0c880e4@redhat.com>
Date: Wed, 6 Dec 2017 15:06:12 -0800
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Subject: [kernel-hardening] Re: [PATCH RFC v6 5/6] fs/proc: Show STACKLEAK metrics in the /proc
 file system
To: Kees Cook <keescook@chromium.org>
Cc: Alexander Popov <alex.popov@linux.com>, kernel-hardening@lists.openwall.com, PaX Team <pageexec@freemail.hu>, Brad Spengler <spender@grsecurity.net>, Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@kernel.org>, Tycho Andersen <tycho@tycho.ws>, Mark Rutland <mark.rutland@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Borislav Petkov <bp@alien8.de>, Thomas Gleixner <tglx@linutronix.de>, "H . Peter Anvin" <hpa@zytor.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, X86 ML <x86@kernel.org>
List-ID: <kernel-hardening.lists.openwall.com>

On 12/06/2017 12:40 PM, Kees Cook wrote:
> On Wed, Dec 6, 2017 at 11:22 AM, Laura Abbott <labbott@redhat.com> wrote:
>> On 12/05/2017 03:33 PM, Alexander Popov wrote:
>>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>>> index 28fa852..3569446 100644
>>> --- a/fs/proc/base.c
>>> +++ b/fs/proc/base.c
>>> @@ -2884,6 +2884,17 @@ static int proc_pid_patch_state(struct seq_file *m,
>>> struct pid_namespace *ns,
>>>    }
>>>    #endif /* CONFIG_LIVEPATCH */
>>>    +#ifdef CONFIG_STACKLEAK_METRICS
>>> +static int proc_lowest_stack(struct seq_file *m, struct pid_namespace
>>> *ns,
>>> +                               struct pid *pid, struct task_struct *task)
>>> +{
>>> +       seq_printf(m, "prev_lowest_stack: %pK\nlowest_stack: %pK\n",
>>> +                  (void *)task->thread.prev_lowest_stack,
>>> +                  (void *)task->thread.lowest_stack);
>>> +       return 0;
>>> +}
>>> +#endif /* CONFIG_STACKLEAK_METRICS */
>>> +
>>
>>
>> This just prints the hashed value with the new pointer leak work.
>> I don't think we want to print the fully exposed value via %px so
>> it's not clear how valuable this proc file is now.
> 
> Maybe print the size, not the location?
> 
> -Kees
> 
Hmmmmm, that starts to overlap with CONFIG_DEBUG_STACK_USAGE.
That's not a bad thing but it would be good to clarify what
this is tracking vs. CONFIG_DEBUG_STACK_USAGE.

Thanks,
Laura