On Mon, Apr 12, 2021 at 03:04:58PM -0400, Chris von Recklinghausen wrote: > On 4/12/21 1:45 PM, Eric Biggers wrote: > > On Mon, Apr 12, 2021 at 10:09:32AM -0400, Chris von Recklinghausen 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. > > > > > > The purpose of the integrity check is to detect possible differences > > > between the memory map used at the time when the hibernation image is > > > about to be loaded into memory and the memory map used at the image > > > creation time, because it is generally unsafe to load the image if the > > > current memory map doesn't match the one used when it was created. so > > > it is not intended as a cryptographic integrity check. > > This still doesn't actually explain why a non-cryptographic checksum is > > sufficient. "Detection of possible differences" could very well require > > cryptographic authentication; it depends on whether malicious changes need to be > > detected or not. > > Hi Eric, > > The cases that the commit comments for 62a03defeabd mention are the same as > for this patch, e.g. > > 1. Without this patch applied, it is possible that BIOS has > provided an inconsistent memory map, but the resume kernel is still > able to restore the image anyway(e.g, E820_RAM region is the superset > of the previous one), although the system might be unstable. So this > patch tries to treat any inconsistent e820 as illegal. > > 2. Another case is, this patch replies on comparing the e820_saved, but > currently the e820_save might not be strictly the same across > hibernation, even if BIOS has provided consistent e820 map - In > theory mptable might modify the BIOS-provided e820_saved dynamically > in early_reserve_e820_mpc_new, which would allocate a buffer from > E820_RAM, and marks it from E820_RAM to E820_RESERVED). > This is a potential and rare case we need to deal with in OS in > the future. > > Maybe they should be added to the comments with this patch as well? In any > case, the above comments only mention detecting consequences of BIOS > issues/actions on the e820 map and not intrusions from attackers requiring > cryptographic protection. Does that seem to be a reasonable explanation to > you? If so I can add these to the commit comments. > > I'll make the other changes you suggest below. > > Thanks, > Those details are still missing the high-level point. Is this just meant to detect non-malicious changes (presumably caused by BIOS bugs), or is it meant to detect malicious changes? That's all that really needs to be mentioned. - Eric
