From: Sean Christopherson Date: Fri, 25 Feb 2022 18:22:48 +0000 (+0000) Subject: KVM: WARN if is_unsync_root() is called on a root without a shadow page X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=5d6a3221562491bee4a83529de5062bf2a138146;p=linux.git KVM: WARN if is_unsync_root() is called on a root without a shadow page WARN and bail if is_unsync_root() is passed a root for which there is no shadow page, i.e. is passed the physical address of one of the special roots, which do not have an associated shadow page. The current usage squeaks by without bug reports because neither kvm_mmu_sync_roots() nor kvm_mmu_sync_prev_roots() calls the helper with pae_root or pml4_root, and 5-level AMD CPUs are not generally available, i.e. no one can coerce KVM into calling is_unsync_root() on pml5_root. Note, this doesn't fix the mess with 5-level nNPT, it just (hopefully) prevents KVM from crashing. Cc: Lai Jiangshan Signed-off-by: Sean Christopherson Message-Id: <20220225182248.3812651-8-seanjc@google.com> Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 825996408465b..3e7c8ad5bed90 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3634,6 +3634,14 @@ static bool is_unsync_root(hpa_t root) */ smp_rmb(); sp = to_shadow_page(root); + + /* + * PAE roots (somewhat arbitrarily) aren't backed by shadow pages, the + * PDPTEs for a given PAE root need to be synchronized individually. + */ + if (WARN_ON_ONCE(!sp)) + return false; + if (sp->unsync || sp->unsync_children) return true;