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

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Date:   Thu, 1 Apr 2021 18:19:57 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Chris von Recklinghausen <crecklin@...hat.com>,
        Simo Sorce <simo@...hat.com>, Dexuan Cui <decui@...rosoft.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] use crc32 instead of md5 for hibernation e820
 integrity check

On Thu, Apr 1, 2021 at 3:59 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Thu, 1 Apr 2021 at 15:34, Rafael J. Wysocki <rafael@...nel.org> wrote:
> >
> > On Thu, Apr 1, 2021 at 2:25 PM Chris von Recklinghausen
> > <crecklin@...hat.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.
> > >
> > > Fixes: 62a03defeabd ("PM / hibernate: Verify the consistent of e820 memory map
> > >        by md5 digest")
> > > Signed-off-by: Chris von Recklinghausen <crecklin@...hat.com>
> > > ---
> > >  arch/x86/power/hibernate.c | 31 +++++++++++++++++--------------
> > >  1 file changed, 17 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/arch/x86/power/hibernate.c b/arch/x86/power/hibernate.c
> > > index cd3914fc9f3d..6a3f4e32e49c 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];
> > >  };
> >
> > No.
> >
> > CRC32 was used here before and it was deemed insufficient.
> >
>
> Why? The git commit log does not have an explanation of this.

IIRC there was an example of a memory map that would produce the same
CRC32 value as the original or something like that.

But that said this code is all about failing more gracefully, so I
guess it isn't a big deal if the failure is more graceful in fewer
cases ...