Messages in this thread | | | Subject | Re: [PATCH v5 1/1] use crc32 instead of md5 for hibernation e820 integrity check | From | Simo Sorce <> | Date | Thu, 08 Apr 2021 11:52:31 -0400 |
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On Thu, 2021-04-08 at 08:26 -0700, Eric Biggers wrote: > On Thu, Apr 08, 2021 at 03:32:38PM +0200, Rafael J. Wysocki wrote: > > On Thu, Apr 8, 2021 at 3:15 PM Chris von Recklinghausen > > <crecklin@redhat.com> wrote: > > > Suspend fails on a system in fips mode because md5 is used for the e820 > > > integrity check and is not available. Use crc32 instead. > > > > > > This patch changes the integrity check algorithm from md5 to > > > crc32. This integrity check is used only to verify accidental > > > corruption of the hybernation data > > > > It isn't used for that. > > > > In fact, it is used to detect differences between the memory map used > > before hibernation and the one made available by the BIOS during the > > subsequent resume. And the check is there, because it is generally > > unsafe to load the hibernation image into memory if the current memory > > map doesn't match the one used when the image was created. > > So what types of "differences" are you trying to detect? If you need to detect > differences caused by someone who maliciously made changes ("malicious" implies > they may try to avoid detection), then you need to use a cryptographic hash > function (or a cryptographic MAC if the hash value isn't stored separately). If > you only need to detect non-malicious changes (normally these would be called > "accidental" changes, but sure, it could be changes that are "intentionally" > made provided that the other side can be trusted to not try to avoid > detection...), then a non-cryptographic checksum would be sufficient.
Wouldn't you also need a signature with a TPM key in that case? An attacker that can change memory maps can also change the hash on disk ? Unless the hash is in an encrypted partition I guess...
Simo.
-- Simo Sorce RHEL Crypto Team Red Hat, Inc
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