From 94bda2f4cd868046094351b06b87d7d1053e990d Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 15 Jul 2022 23:00:13 +0000 Subject: KVM: x86: Reject loading KVM if host.PAT[0] != WB Reject KVM if entry '0' in the host's IA32_PAT MSR is not programmed to writeback (WB) memtype. KVM subtly relies on IA32_PAT entry '0' to be programmed to WB by leaving the PAT bits in shadow paging and NPT SPTEs as '0'. If something other than WB is in PAT[0], at _best_ guests will suffer very poor performance, and at worst KVM will crash the system by breaking cache-coherency expecations (e.g. using WC for guest memory). Signed-off-by: Sean Christopherson Reviewed-by: Maxim Levitsky Message-Id: <20220715230016.3762909-2-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'arch/x86/kvm/x86.c') diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index f389691d8c04..12199c40f2bc 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9141,6 +9141,7 @@ static struct notifier_block pvclock_gtod_notifier = { int kvm_arch_init(void *opaque) { struct kvm_x86_init_ops *ops = opaque; + u64 host_pat; int r; if (kvm_x86_ops.hardware_enable) { @@ -9179,6 +9180,20 @@ int kvm_arch_init(void *opaque) goto out; } + /* + * KVM assumes that PAT entry '0' encodes WB memtype and simply zeroes + * the PAT bits in SPTEs. Bail if PAT[0] is programmed to something + * other than WB. Note, EPT doesn't utilize the PAT, but don't bother + * with an exception. PAT[0] is set to WB on RESET and also by the + * kernel, i.e. failure indicates a kernel bug or broken firmware. + */ + if (rdmsrl_safe(MSR_IA32_CR_PAT, &host_pat) || + (host_pat & GENMASK(2, 0)) != 6) { + pr_err("kvm: host PAT[0] is not WB\n"); + r = -EIO; + goto out; + } + r = -ENOMEM; x86_emulator_cache = kvm_alloc_emulator_cache(); -- cgit v1.2.3