Lucas De Marchi <lucas.de.mar...@gmail.com> writes:
> Sorry to come up with this suggestion only now (and after you have
> already talked to me at LPC). Only after seeing this implementation I
> thought about the implications of having the module signed in this
> format.
...
> I'm worried about performance here. Module loading can take a fair
> amount of boot time. It may not be critical for servers or desktops
> that we rarely boot, but it is for embedded uses.
...
> Letting it in be32 is the simplest solution IMO. it's way simpler then
> the loop above.
...
>> Scanning the module is the least of our issues since we've just copied
>> it and we're about to SHA it.
>
> Yeah, but I don't think we need to scan it one more time. On every
> boot. For every module
Regretfully, I don't have Linus' talent for flamage.
There's no measurable performance impact. Scanning 1k takes about
5usec; we've wasted about enough time on this subject to load a billion
kernel modules.
I know this. Not because I'm brilliant, but because I *measured* it. I
even pulled out my original module signature signing check code, and
that was both faster and simpler. See below.
Your assertion that the length-prepended version is "way simpler" is
wrong. Again, I know this because I *read the code*:
https://git.kernel.org/?p=linux/kernel/git/kasatkin/linux-digsig.git;a=commitdiff;h=19eef6e4e529ccf2b3a6ab5c19dd40f2eaf8fcaf
Don't send any more lazy, unthoughtful mails to the list. It's
disrespectful and makes me grumpy.
Rusty.
PS. Pushed updated version to my kernel.org linux.git/module-signing branch.
#ifdef CONFIG_MODULE_SIG
static int module_sig_check(struct load_info *info,
const void *mod, unsigned long *len)
{
int err = 0;
const unsigned long markerlen = strlen(MODULE_SIG_STRING);
const void *p = mod, *end = mod + *len;
/* Poor man's memmem. */
while ((p = memchr(p, MODULE_SIG_STRING[0], end - p))) {
if (p + markerlen > end)
break;
if (memcmp(p, MODULE_SIG_STRING, markerlen) == 0) {
const void *sig = p + markerlen;
/* Truncate module up to signature. */
*len = p - mod;
err = mod_verify_sig(mod, *len,
sig, end - sig,
&info->sig_ok);
break;
}
p++;
}
/* Not having a signature is only an error if we're strict. */
if (!err && !info->sig_ok && sig_enforce)
err = -EKEYREJECTED;
return err;
}
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