Re: [Regression v5.19-rc1] kernel fails to boot, no console output (Re: [PATCH v12 38/46] x86/sev: Add SEV-SNP feature detection/setup)

[Jeremi Piotrowski]

On Mon, Aug 22, 2022 at 11:39:33AM -0500, Michael Roth wrote:
> On Wed, Aug 17, 2022 at 10:40:40AM +0200, Jeremi Piotrowski wrote:
> > On Tue, Aug 16, 2022 at 10:06:37AM -0500, Michael Roth wrote:
> > > And if that does not avoid the issue, can you retry with the below change
> > > (without the above change in place)?
> > > 
> > >   diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> > >   index 7b668f91c9ab..0b430f98e053 100644
> > >   --- a/arch/x86/kernel/sev.c
> > >   +++ b/arch/x86/kernel/sev.c
> > >   @@ -2073,10 +2073,12 @@ static __init struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
> > >           struct cc_blob_sev_info *cc_info;
> > >   
> > >           /* Boot kernel would have passed the CC blob via boot_params. */
> > >   +#if 0
> > >           if (bp->cc_blob_address) {
> > >                   cc_info = (struct cc_blob_sev_info *)(unsigned long)bp->cc_blob_address;
> > >                   goto found_cc_info;
> > >           }
> > >   +#endif
> > >   
> > >           /*
> > >            * If kernel was booted directly, without the use of the
> > >   @@ -2087,7 +2089,7 @@ static __init struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
> > >           if (!cc_info)
> > >                   return NULL;
> > >   
> > >   -found_cc_info:
> > >   +//found_cc_info:
> > >           if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
> > >                   snp_abort();
> > > 
> > > Trying to see if you're hitting a separate issue or not.
> > 
> > This version boots correctly.
> 
> Hi Jeremi,
> 
> Still haven't been able to reproduce this on my systems, but it looks like
> it's either an issue dereferencing boot_params, or bp->cc_blob_address is
> pointing to garbage, so the cc_info->magic check fails. The latter seems
> more likely, since sme_enable() previously made use of the same boot_params
> pointer without any issues.
> 
> To confirm, please give the below fix a try:
> 
> 
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index 52f989f6acc2..dd6cd0d7c740 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -392,6 +392,13 @@ bool snp_init(struct boot_params *bp)
>         if (!bp)
>                 return false;
> 
> +       /*
> +        * bp->cc_blob_address should only be set by boot/compressed kernel.
> +        * Initialize it to 0 to ensure that uninitialized values from
> +        * buggy bootloaders aren't propagated.
> +        */
> +       bp->cc_blob_address = 0;
> +
>         cc_info = find_cc_blob(bp);
>         if (!cc_info)
>                 return false;
> 

Sorry, couldn't get back to you sooner.
I tested the patch https://lore.kernel.org/lkml/20220823160734.89036-1-michael.roth@xxxxxxx/
and it solves the issue.

Thanks for looking into this
Jeremi

> Thanks!
> 
> -Mike
> 
> > 
> > > 
> > > Thanks,
> > > 
> > > Mike
> > > 
> > >