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Date:   Wed, 4 May 2022 07:54:14 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Andy Shevchenko <andriy.shevchenko@intel.com>
cc:     Stafford Horne <shorne@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Shevchenko <andy@kernel.org>,
        device-mapper development <dm-devel@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Mike Snitzer <msnitzer@redhat.com>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Milan Broz <gmazyland@gmail.com>, Jason@zx2c4.com
Subject: Re: [PATCH v2] hex2bin: make the function hex_to_bin constant-time
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On Wed, 4 May 2022, Andy Shevchenko wrote:

> On Wed, May 04, 2022 at 04:57:35AM -0400, Mikulas Patocka wrote:
> > On Wed, 4 May 2022, Stafford Horne wrote:
> > > On Mon, Apr 25, 2022 at 08:07:48AM -0400, Mikulas Patocka wrote:
> 
> ...
> 
> > > Just a heads up it seems this patch is causing some instability with crypto self
> > > tests on OpenRISC when using a PREEMPT kernel (no SMP).
> > > 
> > > This was reported by Jason A. Donenfeld as it came up in wireguard testing.
> > > 
> > > I am trying to figure out if this is an OpenRISC PREEMPT issue or something
> > > else.
> 
> > That patch is so simple that I can't imagine how could it break the 
> > curve25519 test. Are you sure that you bisected it correctly?
> 
> Can you provide a test cases for hex_to_bin()?

I tested it with this:

#include <stdio.h>

int hex_to_bin(unsigned char c);

int main(void)
{
        int i;
        for (i = 0; i < 256; i++)
                printf("%02x - %d\n", i, hex_to_bin(i));
        return 0;
}

Mikulas