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From:   "Reshetova, Elena" <elena.reshetova@intel.com>
To:     'Kees Cook' <keescook@chromium.org>,
        'Ingo Molnar' <mingo@kernel.org>,
        'Andy Lutomirski' <luto@kernel.org>
CC:     'Theodore Ts'o' <tytso@mit.edu>,
        'David Laight' <David.Laight@aculab.com>,
        'Eric Biggers' <ebiggers3@gmail.com>,
        "'ebiggers@google.com'" <ebiggers@google.com>,
        "'herbert@gondor.apana.org.au'" <herbert@gondor.apana.org.au>,
        'Peter Zijlstra' <peterz@infradead.org>,
        'Daniel Borkmann' <daniel@iogearbox.net>,
        "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
        "'jpoimboe@redhat.com'" <jpoimboe@redhat.com>,
        "'jannh@google.com'" <jannh@google.com>,
        "Perla, Enrico" <enrico.perla@intel.com>,
        "'mingo@redhat.com'" <mingo@redhat.com>,
        "'bp@alien8.de'" <bp@alien8.de>,
        "'tglx@linutronix.de'" <tglx@linutronix.de>,
        "'gregkh@linuxfoundation.org'" <gregkh@linuxfoundation.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
        'Linus Torvalds' <torvalds@linux-foundation.org>,
        'Peter Zijlstra' <a.p.zijlstra@chello.nl>
Subject: RE: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall
Thread-Topic: [PATCH] x86/entry/64: randomize kernel stack offset upon
 syscall
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Date:   Thu, 1 Aug 2019 06:35:47 +0000
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>> The in-stack randomization is really a very small change both code wise and
>> logic wise.
>> It does not affect real workloads and does not require enablement of other
>> features (such as GCC plugins).
>> So, I think we should really reconsider its inclusion.

>I'd agree: the code is tiny and while the benefit can't point to a
>specific issue, it does point to the general weakness of the stack
>offset being predictable which has been a core observation for many
>stack-based attacks.

>If we're going to save state between syscalls (like the 4096 random
>bytes pool), how about instead we just use a single per-CPU long mixed
>with rdtsc saved at syscall exit. That should be a reasonable balance
>between all the considerations and make it trivial for the feature to
>be a boot flag without the extra page of storage, etc.

Sounds like a viable compromise for me. 
Ingo, Andy? 

Best Regards,
Elena.