linux-kernel - Re: [PATCH 1/1] crypto: ccp - Add the SNP_VERIFY

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <aHppQWM5TKPD7JpD@google.com>
Date: Fri, 18 Jul 2025 08:33:21 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: "Pratik R. Sampat" <prsampat@....com>
Cc: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	ashish.kalra@....com, thomas.lendacky@....com, john.allen@....com, 
	herbert@...dor.apana.org.au, bp@...en8.de, michael.roth@....com, aik@....com, 
	pbonzini@...hat.com
Subject: Re: [PATCH 1/1] crypto: ccp - Add the SNP_VERIFY_MITIGATION command

On Wed, Jul 16, 2025, Pratik R. Sampat wrote:
> 
> 
> On 7/10/25 5:45 PM, Sean Christopherson wrote:
> > On Wed, Jul 09, 2025, Pratik R. Sampat wrote:
> >> Hi Sean,
> >>
> >> On 7/8/25 8:57 AM, Sean Christopherson wrote:
> >>> On Mon, Jun 30, 2025, Pratik R. Sampat wrote:
> >>>> The SEV-SNP firmware provides the SNP_VERIFY_MITIGATION command, which
> >>>> can be used to query the status of currently supported vulnerability
> >>>> mitigations and to initiate mitigations within the firmware.
> >>>>
> >>>> See SEV-SNP Firmware ABI specifications 1.58, SNP_VERIFY_MITIGATION for
> >>>> more details.
> >>>
> >>> Nothing here explains why this needs to be exposed directly to userspace.
> >>
> >> The general idea is that not all mitigations may/can be applied
> >> immediately, for ex: some mitigations may require all the guest to be
> >> shutdown before they can be applied. So a host userspace interface to
> >> query+apply mitigations can be useful for that coordination before
> >> attempting to apply the mitigation.
> > 
> > But why expose ioctls to effectively give userspace direct access to firmware?
> > E.g. why not configure firmware mitigations via the kernel's upcoming
> > Attack Vector Controls.
> > 
> > https://lore.kernel.org/all/20250707183316.1349127-1-david.kaplan@amd.com
> 
> Something like Attack Vector Controls may not work in our case, since
> those are designed to protect the kernel from userspace and guests,
> whereas SEV firmware mitigations are focused on protecting guests from
> the hypervisor. Additionally, Attack Vector Controls are managed via
> boot command-line parameters, but maybe we could potentially change
> that by introducing RW interfaces for our case within
> /sys/devices/system/cpu/vector_vulnerabilities (or what the final form
> of this interface ends up being).
> 
> Another option could be to expose this functionality in a subdirectory
> under /sys/firmware/?
> 
> However, with any of these approaches, we would still be giving
> userspace the ability to access and alter the firmware, similar to
> the interfaces that expose features such as Download Firmware EX
> also allow, right?

Not all userspace is created equal, e.g. init_ex_path is a module param, and
(un)loading modules requires CAP_SYS_MODULE.  The expected/desired use cases also
matter, e.g. if there's no use case for toggling mitigations after initial setup,
then the interface presented to userspace could likely be much different than if
there's a "need" to make mitigations fully runtime configurable.