[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAK8P3a076DEDpzRgTRBNLWan-KZyD0LkauWpuO8RFCf-9i1mhA@mail.gmail.com>
Date: Fri, 30 Jun 2017 10:27:06 +0200
From: Arnd Bergmann <arnd@...db.de>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Kees Cook <keescook@...omium.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, Laura Abbott <labbott@...hat.com>,
"the arch/x86 maintainers" <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Russell King - ARM Linux <linux@...linux.org.uk>, Nicolas Pitre <nicolas.pitre@...aro.org>,
Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v2 04/20] gcc-plugins: Add the randstruct plugin
On Fri, Jun 30, 2017 at 9:55 AM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> On 30 June 2017 at 07:35, Arnd Bergmann <arnd@...db.de> wrote:
>> On Fri, Jun 30, 2017 at 12:53 AM, Kees Cook <keescook@...omium.org> wrote:
>>> The first obviously won't fly. The second just bypasses the problem
>>> forcing it to be exposed by other people later. The third is likely
>>> easiest to do now, but reduces the effectiveness of randomization for
>>> architectures that don't have sensitive immediate values. The fourth
>>> sounds not generally useful. The fifth may be unacceptable to arm
>>> maintainers due to performance impacts.
>>
>> I was thinking of the fifth solution, but don't know exactly how to
>> do it. If performance is a concern, I guess we could have separate
>> implementations for randstruct and traditional builds.
>>
>
> Does this not apply to *all* entries in asm-offsets? If so, I don't
> see how it is tractable to fix this in the code, unless we add some
> instrumentation to asm-offsets to whitelist some huge structs and
> error out on new ones. Or perhaps there's really only a handful?
I think the other structs are all small enough:
* thread_info is at most 720 bytes (including crunch+vfp3, which
you wouldn't find in one combined kernel) and not randomized
at the moment
* pt_regs is 72 bytes and I don't see how that would be randomized
* machine_desc would be a candidate for randomizing, but is only
108 bytes
* proc_info_list is 52 bytes and not currently randomized
* vm_area_struct is randomized but only 96 bytes.
* task_struct is clearly large enough, but we only use TSK_ACTIVE_MM
and TSK_STACK_CANARY, both can be fixed with your trick.
> In any case, these particular examples are fairly straightforward,
> since there is no need to preserve the register's value.
>
> ldr r7, [r7, #TSK_STACK_CANARY]
>
> could be replaced with
>
> .if TSK_STACK_CANARAY >= PAGE_SIZE
> add r7, r7, #TSK_STACK_CANARY & PAGE_MASK
> .endif
> ldr r7, [r7, #TSK_STACK_CANARY & ~PAGE_MASK]
Nice!
Arnd
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
