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)

From: Michael Roth
Date: Mon Aug 22 2022 - 12:40:04 EST


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;

Thanks!

-Mike

>
> >
> > Thanks,
> >
> > Mike
> >
> >