From: Sean Christopherson seanjc@google.com
commit 817fa998362d6ea9fabd5e97af8e9e2eb5f0e6f2 upstream.
Factor in the address space (non-SMM vs. SMM) of the target shadow page when recovering potential NX huge pages, otherwise KVM will retrieve the wrong memslot when zapping shadow pages that were created for SMM. The bug most visibly manifests as a WARN on the memslot being non-NULL, but the worst case scenario is that KVM could unaccount the shadow page without ensuring KVM won't install a huge page, i.e. if the non-SMM slot is being dirty logged, but the SMM slot is not.
------------[ cut here ]------------ WARNING: CPU: 1 PID: 3911 at arch/x86/kvm/mmu/mmu.c:7015 kvm_nx_huge_page_recovery_worker+0x38c/0x3d0 [kvm] CPU: 1 PID: 3911 Comm: kvm-nx-lpage-re RIP: 0010:kvm_nx_huge_page_recovery_worker+0x38c/0x3d0 [kvm] RSP: 0018:ffff99b284f0be68 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff99b284edd000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffff9271397024e0 R08: 0000000000000000 R09: ffff927139702450 R10: 0000000000000000 R11: 0000000000000001 R12: ffff99b284f0be98 R13: 0000000000000000 R14: ffff9270991fcd80 R15: 0000000000000003 FS: 0000000000000000(0000) GS:ffff927f9f640000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f0aacad3ae0 CR3: 000000088fc2c005 CR4: 00000000003726e0 Call Trace: <TASK> __pfx_kvm_nx_huge_page_recovery_worker+0x10/0x10 [kvm] kvm_vm_worker_thread+0x106/0x1c0 [kvm] kthread+0xd9/0x100 ret_from_fork+0x2c/0x50 </TASK> ---[ end trace 0000000000000000 ]---
This bug was exposed by commit edbdb43fc96b ("KVM: x86: Preserve TDP MMU roots until they are explicitly invalidated"), which allowed KVM to retain SMM TDP MMU roots effectively indefinitely. Before commit edbdb43fc96b, KVM would zap all SMM TDP MMU roots and thus all SMM TDP MMU shadow pages once all vCPUs exited SMM, which made the window where this bug (recovering an SMM NX huge page) could be encountered quite tiny. To hit the bug, the NX recovery thread would have to run while at least one vCPU was in SMM. Most VMs typically only use SMM during boot, and so the problematic shadow pages were gone by the time the NX recovery thread ran.
Now that KVM preserves TDP MMU roots until they are explicitly invalidated (e.g. by a memslot deletion), the window to trigger the bug is effectively never closed because most VMMs don't delete memslots after boot (except for a handful of special scenarios).
Fixes: eb298605705a ("KVM: x86/mmu: Do not recover dirty-tracked NX Huge Pages") Reported-by: Fabio Coatti fabio.coatti@gmail.com Closes: https://lore.kernel.org/all/CADpTngX9LESCdHVu_2mQkNGena_Ng2CphWNwsRGSMxzDsTj... Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230602010137.784664-1-seanjc@google.com Signed-off-by: Sean Christopherson seanjc@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/mmu/mmu.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -7011,7 +7011,10 @@ static void kvm_recover_nx_huge_pages(st */ slot = NULL; if (atomic_read(&kvm->nr_memslots_dirty_logging)) { - slot = gfn_to_memslot(kvm, sp->gfn); + struct kvm_memslots *slots; + + slots = kvm_memslots_for_spte_role(kvm, sp->role); + slot = __gfn_to_memslot(slots, sp->gfn); WARN_ON_ONCE(!slot); }