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Date: Thu, 2 Feb 2017 23:34:10 +0530
From: Bhupesh Sharma <bhsharma@...hat.com>
To: Kees Cook <keescook@...omium.org>
Cc: "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Daniel Cashman <dcashman@...gle.com>,
Michael Ellerman <mpe@...erman.id.au>, Bhupesh SHARMA <bhupesh.linux@...il.com>,
Alexander Graf <agraf@...e.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>, Anatolij Gustschin <agust@...x.de>,
Alistair Popple <alistair@...ple.id.au>, Matt Porter <mporter@...nel.crashing.org>,
Vitaly Bordug <vitb@...nel.crashing.org>, Scott Wood <oss@...error.net>,
Kumar Gala <galak@...nel.crashing.org>, Daniel Cashman <dcashman@...roid.com>
Subject: Re: [PATCH 1/2] powerpc: mm: support ARCH_MMAP_RND_BITS
Hi Kees,
On Thu, Feb 2, 2017 at 7:55 PM, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Feb 1, 2017 at 9:42 PM, Bhupesh Sharma <bhsharma@...hat.com> wrote:
>> powerpc: arch_mmap_rnd() uses hard-coded values, (23-PAGE_SHIFT) for
>> 32-bit and (30-PAGE_SHIFT) for 64-bit, to generate the random offset
>> for the mmap base address.
>>
>> This value represents a compromise between increased
>> ASLR effectiveness and avoiding address-space fragmentation.
>> Replace it with a Kconfig option, which is sensibly bounded, so that
>> platform developers may choose where to place this compromise.
>> Keep default values as new minimums.
>>
>> This patch makes sure that now powerpc mmap arch_mmap_rnd() approach
>> is similar to other ARCHs like x86, arm64 and arm.
>>
>> Cc: Alexander Graf <agraf@...e.com>
>> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>> Cc: Paul Mackerras <paulus@...ba.org>
>> Cc: Michael Ellerman <mpe@...erman.id.au>
>> Cc: Anatolij Gustschin <agust@...x.de>
>> Cc: Alistair Popple <alistair@...ple.id.au>
>> Cc: Matt Porter <mporter@...nel.crashing.org>
>> Cc: Vitaly Bordug <vitb@...nel.crashing.org>
>> Cc: Scott Wood <oss@...error.net>
>> Cc: Kumar Gala <galak@...nel.crashing.org>
>> Cc: Daniel Cashman <dcashman@...roid.com>
>> Cc: Kees Cook <keescook@...omium.org>
>> Signed-off-by: Bhupesh Sharma <bhsharma@...hat.com>
>> ---
>> arch/powerpc/Kconfig | 34 ++++++++++++++++++++++++++++++++++
>> arch/powerpc/mm/mmap.c | 7 ++++---
>> 2 files changed, 38 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index a8ee573fe610..b4a843f68705 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -22,6 +22,38 @@ config MMU
>> bool
>> default y
>>
>> +config ARCH_MMAP_RND_BITS_MIN
>> + default 5 if PPC_256K_PAGES && 32BIT
>> + default 12 if PPC_256K_PAGES && 64BIT
>> + default 7 if PPC_64K_PAGES && 32BIT
>> + default 14 if PPC_64K_PAGES && 64BIT
>> + default 9 if PPC_16K_PAGES && 32BIT
>> + default 16 if PPC_16K_PAGES && 64BIT
>> + default 11 if PPC_4K_PAGES && 32BIT
>> + default 18 if PPC_4K_PAGES && 64BIT
>> +
>> +# max bits determined by the following formula:
>> +# VA_BITS - PAGE_SHIFT - 4
>> +# for e.g for 64K page and 64BIT = 48 - 16 - 4 = 28
>> +config ARCH_MMAP_RND_BITS_MAX
>> + default 10 if PPC_256K_PAGES && 32BIT
>> + default 26 if PPC_256K_PAGES && 64BIT
>> + default 12 if PPC_64K_PAGES && 32BIT
>> + default 28 if PPC_64K_PAGES && 64BIT
>> + default 14 if PPC_16K_PAGES && 32BIT
>> + default 30 if PPC_16K_PAGES && 64BIT
>> + default 16 if PPC_4K_PAGES && 32BIT
>> + default 32 if PPC_4K_PAGES && 64BIT
>> +
>> +config ARCH_MMAP_RND_COMPAT_BITS_MIN
>> + default 5 if PPC_256K_PAGES
>> + default 7 if PPC_64K_PAGES
>> + default 9 if PPC_16K_PAGES
>> + default 11
>> +
>> +config ARCH_MMAP_RND_COMPAT_BITS_MAX
>> + default 16
>> +
>> config HAVE_SETUP_PER_CPU_AREA
>> def_bool PPC64
>>
>> @@ -100,6 +132,8 @@ config PPC
>> select HAVE_EFFICIENT_UNALIGNED_ACCESS if !(CPU_LITTLE_ENDIAN && POWER7_CPU)
>> select HAVE_KPROBES
>> select HAVE_ARCH_KGDB
>> + select HAVE_ARCH_MMAP_RND_BITS
>> + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
>> select HAVE_KRETPROBES
>> select HAVE_ARCH_TRACEHOOK
>> select HAVE_MEMBLOCK
>> diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
>> index 2f1e44362198..babf59faab3b 100644
>> --- a/arch/powerpc/mm/mmap.c
>> +++ b/arch/powerpc/mm/mmap.c
>> @@ -60,11 +60,12 @@ unsigned long arch_mmap_rnd(void)
>> {
>> unsigned long rnd;
>>
>> - /* 8MB for 32bit, 1GB for 64bit */
>> +#ifdef CONFIG_COMPAT
>> if (is_32bit_task())
>> - rnd = get_random_long() % (1<<(23-PAGE_SHIFT));
>> + rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
>> else
>> - rnd = get_random_long() % (1UL<<(30-PAGE_SHIFT));
>> +#endif
>> + rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
>>
>> return rnd << PAGE_SHIFT;
>> }
>
> Awesome! This looks good to me based on my earlier analysis.
>
> Reviewed-by: Kees Cook <keescook@...omium.org>
Many thanks.
Regards,
Bhupesh
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