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

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Message-ID: <20180905083320.GA28462@soda.linbit>
Date:   Wed, 5 Sep 2018 10:33:20 +0200
From:   Lars Ellenberg <lars.ellenberg@...bit.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     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 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.

> 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.

Thanks!

    Lars