Re: [PATCH v5 1/1] use crc32 instead of md5 for hibernation e820 integrity check

[Chris von Recklinghausen]

On 4/8/21 11:30 AM, Eric Biggers wrote:
> On Thu, Apr 08, 2021 at 09:15:06AM -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. This integrity check is used only to verify accidental
> > corruption of the hybernation data and is not intended as a
> > cryptographic integrity check.
> > Md5 is overkill in this case and also disabled in FIPS mode because it
> > is known to be broken for cryptographic purposes.
> >
> > Fixes: 62a03defeabd ("PM / hibernate: Verify the consistent of e820 memory map
> >         by md5 digest")
> >
> > Tested-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> > Reviewed-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> > Signed-off-by: Chris von Recklinghausen <crecklin@xxxxxxxxxx>
> > ---
> > v1 -> v2
> >     bump up RESTORE_MAGIC
> > v2 -> v3
> >     move embelishment from cover letter to commit comments (no code change)
> > v3 -> v4
> >     add note to comments that md5 isn't used for encryption here.
> > v4 -> v5
> >     reword comment per Simo's suggestion
> >
> >   arch/x86/power/hibernate.c | 35 +++++++++++++++++++----------------
> >   1 file changed, 19 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/x86/power/hibernate.c b/arch/x86/power/hibernate.c
> > index cd3914fc9f3d..b56172553275 100644
> > --- a/arch/x86/power/hibernate.c
> > +++ b/arch/x86/power/hibernate.c
> > @@ -55,31 +55,31 @@ int pfn_is_nosave(unsigned long pfn)
> >   }
> >   
> >   
> > -#define MD5_DIGEST_SIZE 16
> > +#define CRC32_DIGEST_SIZE 16
> >   
> >   struct restore_data_record {
> >   	unsigned long jump_address;
> >   	unsigned long jump_address_phys;
> >   	unsigned long cr3;
> >   	unsigned long magic;
> > -	u8 e820_digest[MD5_DIGEST_SIZE];
> > +	u8 e820_digest[CRC32_DIGEST_SIZE];
> >   };
> >   
> > -#if IS_BUILTIN(CONFIG_CRYPTO_MD5)
> > +#if IS_BUILTIN(CONFIG_CRYPTO_CRC32)
> Should CONFIG_CRYPTO_CRC32 be getting selected from somewhere?


Yes, presumably from the same source that sets CONFIG_CRYPTO_MD5. Also 
presumably there's value to not forcing the check if the config value is 
not set.


> If that is too hard because it would pull in too much of the crypto API, maybe
> using the library interface to CRC-32 (lib/crc32.c) would be a better fit?


Based on my statement above, the intent is to provide a simple drop in 
replacement for md5 so that users of FIPS mode can suspend/resume 
without any errors.

Thanks,

Chris


> - Eric