Date:   Wed, 25 Jan 2023 00:55:09 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     John Allen <john.allen@amd.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        pbonzini@redhat.com, weijiang.yang@intel.com,
        rick.p.edgecombe@intel.com, x86@kernel.org, thomas.lendacky@amd.com
Subject: Re: [RFC PATCH 0/7] SVM guest shadow stack support
Message-ID: <Y9B97dZnFnjEHhVf@google.com>
References: <20221012203910.204793-1-john.allen@amd.com>
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In-Reply-To: <20221012203910.204793-1-john.allen@amd.com>
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On Wed, Oct 12, 2022, John Allen wrote:
> AMD Zen3 and newer processors support shadow stack, a feature designed to
> protect against ROP (return-oriented programming) attacks in which an attacker
> manipulates return addresses on the call stack in order to execute arbitrary
> code. To prevent this, shadow stacks can be allocated that are only used by
> control transfer and return instructions. When a CALL instruction is issued, it
> writes the return address to both the program stack and the shadow stack. When
> the subsequent RET instruction is issued, it pops the return address from both
> stacks and compares them. If the addresses don't match, a control-protection
> exception is raised.
> 
> Shadow stack and a related feature, Indirect Branch Tracking (IBT), are
> collectively referred to as Control-flow Enforcement Technology (CET). However,
> current AMD processors only support shadow stack and not IBT.
> 
> This series adds support for shadow stack in SVM guests and builds upon the
> support added in the CET guest support patch series [1] and the CET kernel
> patch series [2]. Additional patches are required to support shadow stack
> enabled guests in qemu [3] and glibc [4].
> 
> [1]: CET guest support patches
> https://lore.kernel.org/all/20220616084643.19564-1-weijiang.yang@intel.com/
> 
> [2]: Latest CET kernel patches
> https://lore.kernel.org/all/20220929222936.14584-1-rick.p.edgecombe@intel.com/

That dependency chain makes me sad.

Outside of a very shallow comment on the last patch, I don't plan on reviewing
this until the kernel side of things gets out of our way.  When that finally
does happen, I'll definitely prioritize reviewing and merging this and the KVM
Intel series.  I'd love to see this land.

Sorry :-(