linux-kernel - Re: [PATCH] mm: Revert x86_64 and arm64 ELF_ET_DYN

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Message-ID: <CAGXu5jLuBNUeaT4mR7yHCsgX+C=P2+iE0OHeodWaxXyGGtQsyg@mail.gmail.com>
Date:   Tue, 15 Aug 2017 12:02:34 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kostya Serebryany <kcc@...gle.com>,
        Will Deacon <will.deacon@....com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Daniel Micay <danielmicay@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Pratyush Anand <panand@...hat.com>,
        Dong Bo <dongbo4@...wei.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Rik van Riel <riel@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Grzegorz Andrejczuk <grzegorz.andrejczuk@...el.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Reid Kleckner <rnk@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Revert x86_64 and arm64 ELF_ET_DYN_BASE base

ping to akpm to please pick this up for -mm...

On Tue, Aug 8, 2017 at 7:00 PM, Kees Cook <keescook@...omium.org> wrote:
> On Tue, Aug 8, 2017 at 2:34 AM, Will Deacon <will.deacon@....com> wrote:
>> On Mon, Aug 07, 2017 at 01:15:42PM -0700, Kees Cook wrote:
>>> Moving the x86_64 and arm64 PIE base from 0x555555554000 to 0x000100000000
>>> broke AddressSanitizer. This is a partial revert of:
>>>
>>>   commit eab09532d400 ("binfmt_elf: use ELF_ET_DYN_BASE only for PIE")
>>>   commit 02445990a96e ("arm64: move ELF_ET_DYN_BASE to 4GB / 4MB")
>>>
>>> The AddressSanitizer tool has hard-coded expectations about where
>>> executable mappings are loaded. The motivation for changing the PIE
>>> base in the above commits was to avoid the Stack-Clash CVEs that
>>> allowed executable mappings to get too close to heap and stack. This
>>> was mainly a problem on 32-bit, but the 64-bit bases were moved too,
>>> in an effort to proactively protect those systems (proofs of concept
>>> do exist that show 64-bit collisions, but other recent changes to fix
>>> stack accounting and setuid behaviors will minimize the impact).
>>>
>>> The new 32-bit PIE base is fine for ASan (since it matches the ET_EXEC
>>> base), so only the 64-bit PIE base needs to be reverted to let x86 and
>>> arm64 ASan binaries run again. Future changes to the 64-bit PIE base on
>>> these architectures can be made optional once a more dynamic method for
>>> dealing with AddressSanitizer is found. (e.g. always loading PIE into
>>> the mmap region for marked binaries.)
>>>
>>> Reported-by: Kostya Serebryany <kcc@...gle.com>
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Kees Cook <keescook@...omium.org>
>>> ---
>>>  arch/arm64/include/asm/elf.h | 4 ++--
>>>  arch/x86/include/asm/elf.h   | 4 ++--
>>>  2 files changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
>>> index acae781f7359..3288c2b36731 100644
>>> --- a/arch/arm64/include/asm/elf.h
>>> +++ b/arch/arm64/include/asm/elf.h
>>> @@ -114,10 +114,10 @@
>>>
>>>  /*
>>>   * This is the base location for PIE (ET_DYN with INTERP) loads. On
>>> - * 64-bit, this is raised to 4GB to leave the entire 32-bit address
>>> + * 64-bit, this is above 4GB to leave the entire 32-bit address
>>>   * space open for things that want to use the area for 32-bit pointers.
>>>   */
>>> -#define ELF_ET_DYN_BASE              0x100000000UL
>>> +#define ELF_ET_DYN_BASE              (2 * TASK_SIZE_64 / 3)
>>>
>>>  #ifndef __ASSEMBLY__
>>
>> Acked-by: Will Deacon <will.deacon@....com>
>>
>> I assume this is going via akpm like the original commit?
>
> That's my expectation, yup. Thanks for the Ack!
>
> -Kees
>
> --
> Kees Cook
> Pixel Security



-- 
Kees Cook
Pixel Security