linux-kernel - Re: [PATCH] arm64: Clear the stack

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Message-ID: <CAGXu5jLW5FJdRdRXcP=xPOEcQ=Tg+uSi=vj6vQ39iVp=QHSRAQ@mail.gmail.com>
Date:   Fri, 29 Jun 2018 13:25:20 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Alexander Popov <alex.popov@...ux.com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: Clear the stack

On Fri, Jun 29, 2018 at 1:22 PM, Laura Abbott <labbott@...hat.com> wrote:
> On 06/29/2018 01:19 PM, Kees Cook wrote:
>>
>> On Fri, Jun 29, 2018 at 12:05 PM, Laura Abbott <labbott@...hat.com> wrote:
>>>
>>> Implementation of stackleak based heavily on the x86 version
>>>
>>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>>> [...]
>>> +#define current_top_of_stack() (task_stack_page(current) + THREAD_SIZE)
>>> +#define on_thread_stack()      (on_task_stack(current,
>>> current_stack_pointer))
>>
>>
>> nit on types here. I get some warnings:
>>
>> kernel/stackleak.c:55:12: warning: assignment makes integer from
>> pointer without a cast [-Wint-conversion]
>>     boundary = current_top_of_stack();
>>              ^
>> kernel/stackleak.c:65:24: warning: assignment makes integer from
>> pointer without a cast [-Wint-conversion]
>>    current->lowest_stack = current_top_of_stack() - THREAD_SIZE / 64;
>>                          ^
>>
>> So I think this needs to be:
>>
>> +#define current_top_of_stack() ((unsigned long)task_stack_page(current) +
>> \
>> +                                THREAD_SIZE)
>>
>
> Argh, missed that in an amend, can fix for next version if there
> are no other objections to this approach.

No worries! I've made the change locally and will push this out to
-next unless there are objections?

-Kees

-- 
Kees Cook
Pixel Security