Re: [RFC PATCH 0/7] SVM guest shadow stack support

[Yang, Weijiang]

On 3/29/2023 1:51 AM, John Allen wrote:
> On Wed, Jan 25, 2023 at 01:11:44AM +0000, Edgecombe, Rick P wrote:
> > On Wed, 2023-01-25 at 00:55 +0000, Sean Christopherson wrote:
> > > 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@xxxxxxxxx/
> > > > [2]: Latest CET kernel patches
> > https://lore.kernel.org/all/20220929222936.14584-1-rick.p.edgecombe@xxxxxxxxx/
> > > 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.
> > I think all KVM needs is a few patches from the beginning of the host
> > series (the FPU stuff). At one point Weijiang and I had discussed with
> > Paolo and x86 folks that those few could go up with the KVM series if
> > desired.
> Now that the baremetal series has been accepted, how do we want to
> proceed? I think I'd like to send a refreshed version based on the
> version that was accpeted, but I'd want to wait to base it on a new
> version of Weijiang's kvm/vmx series (if one is planned).
>
> Weijiang and Rick,
>
> Are you planning on sending a new version of the kvm/vmx series?

Hi, Allen,

Yes, I'm working on the new version of kvm/vmx series, will cc you when

send it to community.


> Thanks,
> John