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[v2,0/5] KVM: x86/xen: Restrict hypercall MSR index

Message ID 20250215011437.1203084-1-seanjc@google.com (mailing list archive)
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Series KVM: x86/xen: Restrict hypercall MSR index | expand

Message

Sean Christopherson Feb. 15, 2025, 1:14 a.m. UTC 
Harden KVM against goofy userspace by restricting the Xen hypercall MSR
index to the de facto standard synthetic range, 0x40000000 - 0x4fffffff.
This obviously has the potential to break userspace, but I'm fairly confident
it'll be fine (knock wood), and doing nothing is not an option as letting
userspace redirect any WRMSR is at best completely broken.

Patches 2-5 are tangentially related cleanups.

v2:
 - Collect reviews. [Paul, David]
 - Add proper #defines for the range. [David]
 - Drop the syzkaller/stable tags (rely on disallow host writes to fix the
   syzkaller splat]. David

v1: https://lore.kernel.org/all/20250201011400.669483-1-seanjc@google.com

Sean Christopherson (5):
  KVM: x86/xen: Restrict hypercall MSR to unofficial synthetic range
  KVM: x86/xen: Add an #ifdef'd helper to detect writes to Xen MSR
  KVM: x86/xen: Consult kvm_xen_enabled when checking for Xen MSR writes
  KVM: x86/xen: Bury xen_hvm_config behind CONFIG_KVM_XEN=y
  KVM: x86/xen: Move kvm_xen_hvm_config field into kvm_xen

 arch/x86/include/asm/kvm_host.h |  4 ++--
 arch/x86/include/uapi/asm/kvm.h |  3 +++
 arch/x86/kvm/x86.c              |  4 ++--
 arch/x86/kvm/xen.c              | 29 +++++++++++++++++++----------
 arch/x86/kvm/xen.h              | 17 +++++++++++++++--
 5 files changed, 41 insertions(+), 16 deletions(-)


base-commit: 3617c0ee7decb3db3f230b1c844126575fab4d49

Comments

Sean Christopherson Feb. 28, 2025, 5:06 p.m. UTC | #1 
On Fri, 14 Feb 2025 17:14:32 -0800, Sean Christopherson wrote:
> Harden KVM against goofy userspace by restricting the Xen hypercall MSR
> index to the de facto standard synthetic range, 0x40000000 - 0x4fffffff.
> This obviously has the potential to break userspace, but I'm fairly confident
> it'll be fine (knock wood), and doing nothing is not an option as letting
> userspace redirect any WRMSR is at best completely broken.
> 
> Patches 2-5 are tangentially related cleanups.
> 
> [...]

Applied to kvm-x86 xen, with the docs change.  Thanks for the reviews!

[1/5] KVM: x86/xen: Restrict hypercall MSR to unofficial synthetic range
      https://github.com/kvm-x86/linux/commit/5c17848134ab
[2/5] KVM: x86/xen: Add an #ifdef'd helper to detect writes to Xen MSR
      https://github.com/kvm-x86/linux/commit/bb0978d95a55
[3/5] KVM: x86/xen: Consult kvm_xen_enabled when checking for Xen MSR writes
      https://github.com/kvm-x86/linux/commit/a5d7700af6b0
[4/5] KVM: x86/xen: Bury xen_hvm_config behind CONFIG_KVM_XEN=y
      https://github.com/kvm-x86/linux/commit/69e5a7dde965
[5/5] KVM: x86/xen: Move kvm_xen_hvm_config field into kvm_xen
      https://github.com/kvm-x86/linux/commit/26e228ec1695

--
https://github.com/kvm-x86/linux/tree/next