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Message-ID: <8737cxswuk.fsf@concordia.ellerman.id.au>
Date: Tue, 25 Apr 2017 00:29:07 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Balbir Singh <bsingharora@...il.com>, linuxppc-dev@...abs.org
Cc: bhsharma@...hat.com, keescook@...omium.org, kernel-hardening@...ts.openwall.com
Subject: Re: Re: [PATCH v2] powerpc/mm: Add support for runtime configuration of ASLR limits
Balbir Singh <bsingharora@...il.com> writes:
> On Fri, 2017-04-21 at 00:36 +1000, Michael Ellerman wrote:
>> Add powerpc support for mmap_rnd_bits and mmap_rnd_compat_bits, which are two
>> sysctls that allow a user to configure the number of bits of randomness used for
>> ASLR.
...
>
> Could we please suggest that this should not be sent to stable or back-ported
> as the 128T default is new?
I'm not sure I follow. I didn't tag it for stable. Do you mean we should
explicitly mark it as not-for-stable?
If someone sends it to stable@...r I'll be pinged before it goes in and
nak it, if someone wants to backport it (incorrectly) to their own tree
then good luck to them :)
>> 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?
No, shift can only be 29 at most IIRC?
But it's a bit fragile, so I'll change it.
cheers
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