lkml.org 
[lkml]   [2022]   [May]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] hex2bin: make the function hex_to_bin constant-time


On Wed, 4 May 2022, Stafford Horne wrote:

> On Mon, Apr 25, 2022 at 08:07:48AM -0400, Mikulas Patocka wrote:
>
> > From: Mikulas Patocka <mpatocka@redhat.com>
> >
> > -int hex_to_bin(char ch)
> > +int hex_to_bin(unsigned char ch)
> > {
> > - if ((ch >= '0') && (ch <= '9'))
> > - return ch - '0';
> > - ch = tolower(ch);
> > - if ((ch >= 'a') && (ch <= 'f'))
> > - return ch - 'a' + 10;
> > - return -1;
> > + unsigned char cu = ch & 0xdf;
> > + return -1 +
> > + ((ch - '0' + 1) & (unsigned)((ch - '9' - 1) & ('0' - 1 - ch)) >> 8) +
> > + ((cu - 'A' + 11) & (unsigned)((cu - 'F' - 1) & ('A' - 1 - cu)) >> 8);
> > }
> > EXPORT_SYMBOL(hex_to_bin);
>
> Hello,
>
> 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.

Hi

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?

Mikulas

\
 
 \ /
  Last update: 2022-05-04 10:59    [W:0.124 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site