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

[Edgecombe, Rick P]

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.