linux-kernel - Re: [PATCH] crypto: jitterentropy

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Message-ID: <CAMj1kXFC=6G1pqFAcjASrKJfzguO3k9Rv-7NsmTaX8qNre5TGw@mail.gmail.com>
Date:   Mon, 5 Oct 2020 08:24:46 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "Stephan M??ller" <smueller@...onox.de>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        kernel test robot <lkp@...el.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] crypto: jitterentropy - bind statically into kernel

On Mon, 5 Oct 2020 at 08:19, Christoph Hellwig <hch@...radead.org> wrote:
>
> On Sun, Oct 04, 2020 at 11:16:10PM +0200, Ard Biesheuvel wrote:
> > On Sun, 4 Oct 2020 at 20:48, Stephan M??ller <smueller@...onox.de> wrote:
> > >
> > > The RISC-V architecture is about to implement the callback
> > > random_get_entropy with a function that is not exported to modules.
> >
> > Why is that? Wouldn't it be better to export the symbol instead?
>
> get_cycles is a low-level time keeping detail that really should not
> be exported, and at least for RISC-V this would be the only modular
> user.  Once that is sorted out I'll audit other common architectures
> to drop the export, as it isn't something that should be used in ramdom
> driver code.

Fair enough.

But this means we should fix the jitterentropy driver rather than
sidestepping the issue by only allowing it to be built in a way where
we don't happen to notice that the symbol in question is not meant for
general consumption.

If jitterentropy is a special case, we could put a alternate
non-'static inline' version of random_get_entropy() in the core
kernel, and only export it if JITTER_ENTROPY is built as a module in
the first place. But I'd prefer it if jitterentropy switches to an API
that is suitable for driver consumption.