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Date: Tue, 25 Apr 2017 08:44:18 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Kees Cook <keescook@...omium.org>
Cc: Balbir Singh <bsingharora@...il.com>, "linuxppc-dev\@ozlabs.org" <linuxppc-dev@...abs.org>, Bhupesh Sharma <bhsharma@...hat.com>, "kernel-hardening\@lists.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: Re: [PATCH v2] powerpc/mm: Add support for runtime configuration of ASLR limits
Kees Cook <keescook@...omium.org> writes:
> On Mon, Apr 24, 2017 at 7:29 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
>> Balbir Singh <bsingharora@...il.com> writes:
>>>> diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
>>>> index a5d9ef59debe..6141cfff634e 100644
>>>> --- a/arch/powerpc/mm/mmap.c
>>>> +++ b/arch/powerpc/mm/mmap.c
>>>> @@ -59,13 +59,14 @@ static inline int mmap_is_legacy(void)
>>>>
>>>> unsigned long arch_mmap_rnd(void)
>>>> {
>>>> - unsigned long rnd;
>>>> + unsigned long shift, rnd;
>>>>
>>>> - /* 8MB for 32bit, 1GB for 64bit */
>>>> + shift = mmap_rnd_bits;
>>>> +#ifdef CONFIG_COMPAT
>>>> if (is_32bit_task())
>>>> - rnd = get_random_long() % (1<<(23-PAGE_SHIFT));
>>>> - else
>>>> - rnd = get_random_long() % (1UL<<(30-PAGE_SHIFT));
>>>> + shift = mmap_rnd_compat_bits;
>>>> +#endif
>>>> + rnd = get_random_long() % (1 << shift);
>>>
>>> Nitpick, 1 should be 1UL?
>
> Nice catch!
>
>> No, shift can only be 29 at most IIRC?
>
> The largest value in the kconfigs is 33?
Yeah you're right, for the 4K page kernel it can be 33.
Will fix.
cheers
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