linux-kernel - Re: [PATCH] x86/microcode: Allow early loading without initrd

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Thu, 30 Apr 2015 10:18:14 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Borislav Petkov <bp@...en8.de>, Alexander Hirsch <1zeeky@...il.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/microcode: Allow early loading without initrd

On Sun, Apr 26, 2015, at 13:16, Borislav Petkov wrote:
> * the early loader was done with initrd in mind and it was/still is its
> main source for microcode blobs early in the boot. So if we want to
> make it not-mandatory, then the driver needs to be reorganized so that
> builtin blobs and initrd blobs loading paths are cleanly untangled. The
> ifdeffery thing might work now but is certainly not future-proof so it
> would need to be designed in a cleaner way.
> 
> Perhaps something like a microcode cache of patches the AMD loader has,
> all decoupled from the loading paths or so... I don't have a good idea
> right now. I'll have to think about it.

Well, the *early* Intel driver does have a cache of sorts. It could use (a lot of) love, though...

The "cache" in the early intel microcode update driver is implemented by mc_saved_in_initrd[].  It is currently sub-optimal, in that it has MAX_UCODE_COUNT slots (128 slots).

The worst-case real-world fill of this cache is, currently, 7 slots (processor signature 0x6FB). The typical fill would be 1-4 slots.

If we change the code to store at maximum one microcode per pfmask bit plus some other details to handle the "processor does not support pfmask, so it is all zeroes" special case, we can safely change MAX_UCODE_COUNT to either 8 or 9, depending on implementation details.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/