linux-kernel - [PATCH 0/5] KVM: x86/xen: Restrict hypercall MSR index

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Message-ID: <20250201011400.669483-1-seanjc@google.com>
Date: Fri, 31 Jan 2025 17:13:55 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	David Woodhouse <dwmw2@...radead.org>, Paul Durrant <paul@....org>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzbot+cdeaeec70992eca2d920@...kaller.appspotmail.com, 
	Joao Martins <joao.m.martins@...cle.com>, David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH 0/5] KVM: x86/xen: Restrict hypercall MSR index

Address a syzkaller splat 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, and at worst
could be used to exploit paths in KVM that directly write hardcoded MSRs.

Patches 2-5 are tangentially related cleanups.

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/kvm/x86.c              |  4 ++--
 arch/x86/kvm/xen.c              | 28 ++++++++++++++++++----------
 arch/x86/kvm/xen.h              | 17 +++++++++++++++--
 4 files changed, 37 insertions(+), 16 deletions(-)


base-commit: eb723766b1030a23c38adf2348b7c3d1409d11f0
-- 
2.48.1.362.g079036d154-goog