From: dcashman@android•com (Daniel Cashman)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v4 4/4] x86: mm: support ARCH_MMAP_RND_BITS.
Date: Tue, 1 Dec 2015 10:19:32 -0800 [thread overview]
Message-ID: <565DE4B4.5050305@android.com> (raw)
In-Reply-To: <CAGXu5j+Wj_=27gsYStV5OuwNSznux7MtDcMuYe5wM2ORrna_TQ@mail.gmail.com>
On 11/30/2015 04:03 PM, Kees Cook wrote:
> On Thu, Nov 26, 2015 at 2:59 PM, Daniel Cashman <dcashman@android•com> wrote:
>> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
>> index 844b06d..647fecf 100644
>> --- a/arch/x86/mm/mmap.c
>> +++ b/arch/x86/mm/mmap.c
>> @@ -69,14 +69,14 @@ unsigned long arch_mmap_rnd(void)
>> {
>> unsigned long rnd;
>>
>> - /*
>> - * 8 bits of randomness in 32bit mmaps, 20 address space bits
>> - * 28 bits of randomness in 64bit mmaps, 40 address space bits
>> - */
>> if (mmap_is_ia32())
>> - rnd = (unsigned long)get_random_int() % (1<<8);
>> +#ifdef CONFIG_COMPAT
>> + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits);
>> +#else
>> + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
>> +#endif
>> else
>> - rnd = (unsigned long)get_random_int() % (1<<28);
>> + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
>>
>> return rnd << PAGE_SHIFT;
>> }
>> --
>> 2.6.0.rc2.230.g3dd15c0
>>
>
> Can you rework this logic to look more like the arm64 one? I think
> it's more readable as:
>
> #ifdef CONFIG_COMPAT
> if (mmap_is_ia32())
> rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits);
> else
> #endif
> rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
>
> -Kees
>
There is a subtle difference between the two that requires this
difference. the x86 code was written to be used by both 32-bit and
64-bit kernels, whereas the arm64 code runs only for 64-bit. The
assumption I've made with arm64 is that TIF_32BIT should never be set if
CONFIG_COMPAT is not set, but with x86 we could encounter a 32-bit
application without CONFIG_COMPAT, in which case it should use the
default mmap_rnd_bits, not compat, since there is no compat.
-Dan
next prev parent reply other threads:[~2015-12-01 18:19 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-26 22:59 [PATCH v4 0/4] Allow customizable random offset to mmap_base address Daniel Cashman
2015-11-26 22:59 ` [PATCH v4 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR Daniel Cashman
2015-11-26 22:59 ` [PATCH v4 2/4] arm: mm: support ARCH_MMAP_RND_BITS Daniel Cashman
2015-11-26 22:59 ` [PATCH v4 3/4] arm64: " Daniel Cashman
2015-11-26 22:59 ` [PATCH v4 4/4] x86: " Daniel Cashman
2015-12-01 0:03 ` Kees Cook
2015-12-01 18:19 ` Daniel Cashman [this message]
2015-11-30 23:54 ` [PATCH v4 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR Andrew Morton
2015-12-01 0:01 ` Andrew Morton
2015-12-01 0:04 ` Kees Cook
2015-12-01 0:18 ` Andrew Morton
2015-12-01 0:47 ` Daniel Cashman
2015-12-01 0:55 ` Eric W. Biederman
2015-12-01 22:09 ` Andrew Morton
2015-12-01 1:00 ` Kees Cook
2015-12-01 0:05 ` Kees Cook
2015-11-26 23:24 ` [PATCH v4 0/4] Allow customizable random offset to mmap_base address Daniel Cashman
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