From d2df592fd8c6c14a43e08314a91101d60b32da01 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 18 Feb 2021 09:55:39 -0500 Subject: [PATCH] KVM: nSVM: prepare guest save area while is_guest_mode is true Right now, enter_svm_guest_mode is calling nested_prepare_vmcb_save and nested_prepare_vmcb_control. This results in is_guest_mode being false until the end of nested_prepare_vmcb_control. This is a problem because nested_prepare_vmcb_save can in turn cause changes to the intercepts and these have to be applied to the "host VMCB" (stored in svm->nested.hsave) and then merged with the VMCB12 intercepts into svm->vmcb. In particular, without this change we forget to set the CR0 read and CR0 write intercepts when running a real mode L2 guest with NPT disabled. The guest is therefore able to see the CR0.PG bit that KVM sets to enable "paged real mode". This patch fixes the svm.flat mode_switch test case with npt=0. There are no other problematic calls in nested_prepare_vmcb_save. Moving is_guest_mode to the end is done since commit 06fc7772690d ("KVM: SVM: Activate nested state only when guest state is complete", 2010-04-25). However, back then KVM didn't grab a different VMCB when updating the intercepts, it had already copied/merged L1's stuff to L0's VMCB, and then updated L0's VMCB regardless of is_nested(). Later recalc_intercepts was introduced in commit 384c63684397 ("KVM: SVM: Add function to recalculate intercept masks", 2011-01-12). This introduced the bug, because recalc_intercepts now throws away the intercept manipulations that svm_set_cr0 had done in the meanwhile to svm->vmcb. [1] https://lore.kernel.org/kvm/1266493115-28386-1-git-send-email-joerg.roedel@amd.com/ Reviewed-by: Sean Christopherson Tested-by: Vitaly Kuznetsov Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/nested.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index 92d3aaaac612..35891d9a1099 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -469,8 +469,8 @@ int enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb12_gpa, svm->nested.vmcb12_gpa = vmcb12_gpa; load_nested_vmcb_control(svm, &vmcb12->control); - nested_prepare_vmcb_save(svm, vmcb12); nested_prepare_vmcb_control(svm); + nested_prepare_vmcb_save(svm, vmcb12); ret = nested_svm_load_cr3(&svm->vcpu, vmcb12->save.cr3, nested_npt_enabled(svm)); -- GitLab