linux-kernel - Re: [PATCH v7] drbd: Convert from ahash to shash

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Date:   Wed, 5 Sep 2018 09:04:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Kees Cook <keescook@...omium.org>, Jens Axboe <axboe@...nel.dk>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        linux-block <linux-block@...r.kernel.org>,
        drbd-dev@...ts.linbit.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7] drbd: Convert from ahash to shash

On Wed, Sep 5, 2018 at 1:33 AM, Lars Ellenberg
<lars.ellenberg@...bit.com> wrote:
> On Tue, Sep 04, 2018 at 08:04:18PM -0700, Kees Cook wrote:
>> On Mon, Sep 3, 2018 at 11:04 PM, Kees Cook <keescook@...omium.org> wrote:
>> > On Mon, Aug 6, 2018 at 4:32 PM, Kees Cook <keescook@...omium.org> wrote:
>> >> In preparing to remove all stack VLA usage from the kernel[1], this
>> >> removes the discouraged use of AHASH_REQUEST_ON_STACK in favor of
>> >> the smaller SHASH_DESC_ON_STACK by converting from ahash-wrapped-shash
>> >> to direct shash. By removing a layer of indirection this both improves
>> >> performance and reduces stack usage. The stack allocation will be made
>> >> a fixed size in a later patch to the crypto subsystem.
>> >>
>> >> The bulk of the lines in this change are simple s/ahash/shash/, but the
>> >> main logic differences are in drbd_csum_ee() and drbd_csum_bio(), which
>> >> externalizes the page walking with k(un)map_atomic() instead of using
>> >> scattergather.
>> >
>> > Hi Lars! How does this look to you? If you can Ack I assume Jens would
>> > be able to take this.
>
> Sure, I should have ACKed it a month ago already.  As I said, I believe
> you the crypto. And you added the kmap_atomic as I pointed out.
> All good.

Great, thanks! Jens, can you take this?

>> FWIW I've tested a simple drbd configuration before/after this change
>> and things seem to be working correctly.
>
> You'd need "data-integrity-alg" set (or "verify-alg", and then have it
> do an online-verify) to excercise the crypto stuff,
> and you'd need a highmem system (are these still out there?)
> to have the kmap not be a no-op.  But I don't see any potential problem.

While I don't have a highmem system, I've confirmed that
data-integrity-alg and verify-alg are both working for me.

Thanks!

-Kees

-- 
Kees Cook
Pixel Security