linux-kernel - Re: [PATCH] ima: dynamically allocate shash

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Message-ID: <CAK8P3a1Q2JG3KBYNYgWg0_XtGUufNc6zuqcUBqiGSaBRp+au-w@mail.gmail.com>
Date:   Mon, 17 Jun 2019 22:08:02 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        linux-integrity@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ima: dynamically allocate shash_desc

On Mon, Jun 17, 2019 at 8:08 PM Mimi Zohar <zohar@...ux.ibm.com> wrote:
>
> On Mon, 2019-06-17 at 11:55 -0400, Mimi Zohar wrote:
> > On Mon, 2019-06-17 at 13:20 +0200, Arnd Bergmann wrote:
> > > On 32-bit ARM, we get a warning about excessive stack usage when
> > > building with clang.
> > >
> > > security/integrity/ima/ima_crypto.c:504:5: error: stack frame size
> > > of 1152 bytes in function 'ima_calc_field_array_hash' [-Werror,-
> > > Wframe-larger-than=]
> >
> > I'm definitely not seeing this.  Is this problem a result of non
> > upstreamed patches?  For sha1, currently the only possible hash
> > algorithm, I'm seeing 664.

You won't see it with gcc, only with clang in some randconfig builds,
I suppose only when KASAN is enabled.

> Every time a measurement is added to the measurement list, the memory
> would be allocated/freed.  The frequency of new measurements is policy
> dependent.  For performance reasons, I'd prefer if the allocation
> remains on the stack.

Is there a way to preallocate the shash_desc instead? That would
avoid the overhead.

        Arnd