linux-kernel - Re: [PATCH] Fix kexec forbidding kernels signed with custom platform keys to boot

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Date:   Thu, 16 Aug 2018 08:52:06 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     Yannik Sembritzki <yannik@...britzki.me>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Peter Anvin <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Baoquan He <bhe@...hat.com>,
        "Justin M. Forbes" <jforbes@...hat.com>
Subject: Re: [PATCH] Fix kexec forbidding kernels signed with custom platform
 keys to boot

On 08/15/18 at 01:42pm, Vivek Goyal wrote:
> On Wed, Aug 15, 2018 at 07:27:33PM +0200, Yannik Sembritzki wrote:
> > Would this be okay?
> 
> [ CC dave young, Baoquan, Justin Forbes]
> 
> Hi Yannik,
> 
> I am reading that bug and wondering that what broke it. It used to work,
> so some change broke it. 
> 
> Justin said that we have been signing fedora kernels with fedora keys so
> looks like no change there.
> 
> Previously, I think all the keys used to go in system keyring and it
> used to work. Is it somehow because of split in builtin keyring and
> secondary system keyring. Could it be that fedora key used to show
> up in system keyring previously and it worked but now it shows up
> in secondary system keyring and by default we don't use keys from
> that keyring for signature verification?

There was a Fedora bug below:
https://bugzilla.redhat.com/show_bug.cgi?id=1470995

I posted a fix here but bobody responsed, I think I obviously did not
consider the "trust build system only" point from Linus:
http://lists.infradead.org/pipermail/kexec/2017-November/019632.html

But either above patch or defining a macro for the "1UL" in cert header
file works.

Since nobody reviewed my patch so later I submitted a Fedora only patch
which is similar with Yannik's and merged in Fedora tree:
https://bugzilla.redhat.com/attachment.cgi?id=1450772&action=edit

> 
> Thanks
> Vivek
> 
> > 
> > diff --git a/arch/x86/kernel/kexec-bzimage64.c
> > b/arch/x86/kernel/kexec-bzimage64.c
> > index 7326078e..2ba47e24 100644
> > --- a/arch/x86/kernel/kexec-bzimage64.c
> > +++ b/arch/x86/kernel/kexec-bzimage64.c
> > @@ -41,6 +41,9 @@
> >  #define MIN_KERNEL_LOAD_ADDR   0x100000
> >  #define MIN_INITRD_LOAD_ADDR   0x1000000
> >  
> > +// Allow both builtin trusted keys and secondary trusted keys
> > +#define TRUST_FULL_KEYRING     (void *)1UL
> > +
> >  /*
> >   * This is a place holder for all boot loader specific data structure which
> >   * gets allocated in one call but gets freed much later during cleanup
> > @@ -532,7 +535,7 @@ static int bzImage64_cleanup(void *loader_data)
> >  static int bzImage64_verify_sig(const char *kernel, unsigned long
> > kernel_len)
> >  {
> >         return verify_pefile_signature(kernel, kernel_len,
> > -                                      NULL,
> > +                                      TRUST_FULL_KEYRING,
> >                                        VERIFYING_KEXEC_PE_SIGNATURE);
> >  }
> >  #endif
> > --
> > 
> > On 15.08.2018 18:54, Linus Torvalds wrote:
> > > This needs more people involved, and at least a sign-off.
> > >
> > > It looks ok, but I think we need a #define for the magical (void *)1UL
> > > thing. I see the use in verify_pkcs7_signature(), but still.
> > >
> > >               Linus
> > >
> > >
> > >
> > > On Wed, Aug 15, 2018 at 3:11 AM Yannik Sembritzki <yannik@...britzki.me> wrote:
> > >> ---
> > >>  arch/x86/kernel/kexec-bzimage64.c | 2 +-
> > >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
> > >> index 7326078e..eaaa125d 100644
> > >> --- a/arch/x86/kernel/kexec-bzimage64.c
> > >> +++ b/arch/x86/kernel/kexec-bzimage64.c
> > >> @@ -532,7 +532,7 @@ static int bzImage64_cleanup(void *loader_data)
> > >>  static int bzImage64_verify_sig(const char *kernel, unsigned long kernel_len)
> > >>  {
> > >>         return verify_pefile_signature(kernel, kernel_len,
> > >> -                                      NULL,
> > >> +                                      (void *)1UL,
> > >>                                        VERIFYING_KEXEC_PE_SIGNATURE);
> > >>  }
> > >>  #endif
> > >> --
> > >> 2.17.1
> > >>
> > >> The exact scenario under which this issue occurs is described here:
> > >> https://bugzilla.redhat.com/show_bug.cgi?id=1554113
> > >>
> > 

Thanks
Dave