[RFC PATCH v3 0/8] SVM guest shadow stack support

[John Allen]

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]. Additional
patches are required to support shadow stack enabled guests in qemu [2]
and glibc [3].

[1]: CET guest support patches (v5)
https://lore.kernel.org/all/20230803042732.88515-1-weijiang.yang@xxxxxxxxx/

[2]: CET qemu patches
https://patchwork.ozlabs.org/project/qemu-devel/patch/20201013051935.6052-2-weijiang.yang@xxxxxxxxx/

[3]: glibc tree containing necessary updates
https://gitlab.com/x86-glibc/glibc/-/tree/users/hjl/cet/master/

---

v2:
  - Rebased on v3 of the Intel CET virtualization series, dropping the
    patch that moved cet_is_msr_accessible to common code as that has
    been pulled into the Intel series.
  - Minor change removing curly brackets around if statement introduced
    in patch 6/6.
v3:
  - Rebased on v5 of the Intel CET virtualization series.
  - Add patch changing the name of vmplX_ssp SEV-ES save area fields to
    plX_ssp.
  - Merge this series intended for KVM with the separate guest kernel
    patch (now patch 7/8).
  - Update MSR passthrough code to conditionally pass through shadow
    stack MSRS based on both host and guest support.
  - Don't save PL0_SSP, PL1_SSP, and PL2_SSP MSRs on SEV-ES VMRUN as
    these are currently unused.
  
John Allen (8):
  KVM: x86: SVM: Emulate reads and writes to shadow stack MSRs
  KVM: x86: SVM: Update dump_vmcb with shadow stack save area additions
  KVM: x86: SVM: Pass through shadow stack MSRs
  KVM: SVM: Rename vmplX_ssp -> plX_ssp
  KVM: SVM: Save shadow stack host state on VMRUN
  KVM: SVM: Add MSR_IA32_XSS to the GHCB for hypervisor kernel
  x86/sev-es: Include XSS value in GHCB CPUID request
  KVM: SVM: Add CET features to supported_xss

 arch/x86/include/asm/svm.h   |  9 +++---
 arch/x86/kernel/sev-shared.c | 15 ++++++++++
 arch/x86/kvm/svm/sev.c       | 21 ++++++++++++--
 arch/x86/kvm/svm/svm.c       | 53 ++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.h       |  2 +-
 5 files changed, 93 insertions(+), 7 deletions(-)

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2.39.1