linux-kernel - Re: [PATCH v3 3/3] x86/sev: Fix broken SNP support with KVM module built-in

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Z6O8p96ExhWFEn_9@google.com>
Date: Wed, 5 Feb 2025 11:31:51 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Vasant Hegde <vasant.hegde@....com>
Cc: Ashish Kalra <Ashish.Kalra@....com>, pbonzini@...hat.com, tglx@...utronix.de, 
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, 
	hpa@...or.com, thomas.lendacky@....com, john.allen@....com, 
	herbert@...dor.apana.org.au, davem@...emloft.net, joro@...tes.org, 
	suravee.suthikulpanit@....com, will@...nel.org, robin.murphy@....com, 
	michael.roth@....com, dionnaglaze@...gle.com, nikunj@....com, ardb@...nel.org, 
	kevinloughlin@...gle.com, Neeraj.Upadhyay@....com, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org, 
	linux-coco@...ts.linux.dev, iommu@...ts.linux.dev
Subject: Re: [PATCH v3 3/3] x86/sev: Fix broken SNP support with KVM module built-in

On Wed, Feb 05, 2025, Vasant Hegde wrote:
> On 2/5/2025 8:47 PM, Sean Christopherson wrote:
> > On Wed, Feb 05, 2025, Vasant Hegde wrote:
> >>> @@ -3318,6 +3326,9 @@ static int __init iommu_go_to_state(enum iommu_init_state state)
> >>>  		ret = state_next();
> >>>  	}
> >>>  
> >>> +	if (ret && !amd_iommu_snp_en && cc_platform_has(CC_ATTR_HOST_SEV_SNP))
> >>
> >>
> >> I think we should clear when `amd_iommu_snp_en` is true.
> > 
> > That doesn't address the case where amd_iommu_prepare() fails, because amd_iommu_snp_en
> > will be %false (its init value) and the RMP will be uninitialized, i.e.
> > CC_ATTR_HOST_SEV_SNP will be incorrectly left set.
> 
> You are right. I missed early failure scenarios :-(
> 
> > 
> > And conversely, IMO clearing CC_ATTR_HOST_SEV_SNP after initializing the IOMMU
> > and RMP is wrong as well.  Such a host is probably hosed regardless, but from
> > the CPU's perspective, SNP is supported and enabled.
> 
> So we don't want to clear  CC_ATTR_HOST_SEV_SNP after RMP initialization -OR-
> clear for all failures?

I honestly don't know, because the answer largely depends on what happens with
hardware.  I asked in an earlier version of this series if IOMMU initialization
failure after the RMP is configured is even survivable.

For this series, I think it makes sense to match the existing behavior, unless
someone from AMD can definitively state that we should do something different.
And the existing behavior is that amd_iommu_snp_en and CC_ATTR_HOST_SEV_SNP will
be left set if the IOMMU completes iommu_snp_enable(), and the kernel completes
RMP setup.