This is a note to let you know that I've just added the patch titled
KVM: nVMX: Fix bug of injecting L2 exception into L1
to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: kvm-nvmx-fix-bug-of-injecting-l2-exception-into-l1.patch and it can be found in the queue-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From 5c7d4f9ad39d980728b39752304ce10bb2960cbf Mon Sep 17 00:00:00 2001
From: Liran Alon liran.alon@oracle.com Date: Sun, 19 Nov 2017 18:25:43 +0200 Subject: KVM: nVMX: Fix bug of injecting L2 exception into L1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit
From: Liran Alon liran.alon@oracle.com
commit 5c7d4f9ad39d980728b39752304ce10bb2960cbf upstream.
kvm_clear_exception_queue() should clear pending exception. This also includes exceptions which were only marked pending but not yet injected. This is because exception.pending is used for both L1 and L2 to determine if an exception should be raised to guest. Note that an exception which is pending but not yet injected will be raised again once the guest will be resumed.
Consider the following scenario: 1) L0 KVM with ignore_msrs=false. 2) L1 prepare vmcs12 with the following: a) No intercepts on MSR (MSR_BITMAP exist and is filled with 0). b) No intercept for #GP. c) vmx-preemption-timer is configured. 3) L1 enters into L2. 4) L2 reads an unhandled MSR that exists in MSR_BITMAP (such as 0x1fff).
L2 RDMSR could be handled as described below: 1) L2 exits to L0 on RDMSR and calls handle_rdmsr(). 2) handle_rdmsr() calls kvm_inject_gp() which sets KVM_REQ_EVENT, exception.pending=true and exception.injected=false. 3) vcpu_enter_guest() consumes KVM_REQ_EVENT and calls inject_pending_event() which calls vmx_check_nested_events() which sees that exception.pending=true but nested_vmx_check_exception() returns 0 and therefore does nothing at this point. However let's assume it later sees vmx-preemption-timer expired and therefore exits from L2 to L1 by calling nested_vmx_vmexit(). 4) nested_vmx_vmexit() calls prepare_vmcs12() which calls vmcs12_save_pending_event() but it does nothing as exception.injected is false. Also prepare_vmcs12() calls kvm_clear_exception_queue() which does nothing as exception.injected is already false. 5) We now return from vmx_check_nested_events() with 0 while still having exception.pending=true! 6) Therefore inject_pending_event() continues and we inject L2 exception to L1!...
This commit will fix above issue by changing step (4) to clear exception.pending in kvm_clear_exception_queue().
Fixes: 664f8e26b00c ("KVM: X86: Fix loss of exception which has not yet been injected") Signed-off-by: Liran Alon liran.alon@oracle.com Reviewed-by: Nikita Leshenko nikita.leshchenko@oracle.com Reviewed-by: Krish Sadhukhan krish.sadhukhan@oracle.com Signed-off-by: Krish Sadhukhan krish.sadhukhan@oracle.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Radim Krčmář rkrcmar@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/vmx.c | 1 - arch/x86/kvm/x86.h | 1 + 2 files changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -11255,7 +11255,6 @@ static int vmx_check_nested_events(struc if (block_nested_events) return -EBUSY; nested_vmx_inject_exception_vmexit(vcpu, exit_qual); - vcpu->arch.exception.pending = false; return 0; }
--- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -12,6 +12,7 @@
static inline void kvm_clear_exception_queue(struct kvm_vcpu *vcpu) { + vcpu->arch.exception.pending = false; vcpu->arch.exception.injected = false; }
Patches currently in stable-queue which might be from liran.alon@oracle.com are
queue-4.15/kvm-nvmx-fix-bug-of-injecting-l2-exception-into-l1.patch queue-4.15/kvm-nvmx-fix-races-when-sending-nested-pi-while-dest-enters-leaves-l2.patch