Commit 83af5e65 authored Oct 03, 2019 by Tom Lendacky Committed by Paolo Bonzini Oct 22, 2019

KVM: SVM: Guard against DEACTIVATE when performing WBINVD/DF_FLUSH

The SEV firmware DEACTIVATE command disassociates an SEV guest from an
ASID, clears the WBINVD indicator on all threads and indicates that the
SEV firmware DF_FLUSH command must be issued before the ASID can be
re-used. The SEV firmware DF_FLUSH command will return an error if a
WBINVD has not been performed on every thread before it has been invoked.
A window exists between the WBINVD and the invocation of the DF_FLUSH
command where an SEV firmware DEACTIVATE command could be invoked on
another thread, clearing the WBINVD indicator. This will cause the
subsequent SEV firmware DF_FLUSH command to fail which, in turn, results
in the SEV firmware ACTIVATE command failing for the reclaimed ASID.
This results in the SEV guest failing to start.

Use a mutex to close the WBINVD/DF_FLUSH window by obtaining the mutex
before the DEACTIVATE and releasing it after the DF_FLUSH. This ensures
that any DEACTIVATE cannot run before a DF_FLUSH has completed.

Fixes: 59414c98 ("KVM: SVM: Add support for KVM_SEV_LAUNCH_START command")
Tested-by: David Rientjes <rientjes@google.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent e3b9a9e1

arch/x86/kvm/svm.c

+20 −0

Original line number	Diff line number	Diff line
		@@ -418,6 +418,7 @@ enum {

		#define VMCB_AVIC_APIC_BAR_MASK 0xFFFFFFFFFF000ULL

		static DEFINE_MUTEX(sev_deactivate_lock);
		static DEFINE_MUTEX(sev_bitmap_lock);
		static unsigned int max_sev_asid;
		static unsigned int min_sev_asid;
		@@ -1756,10 +1757,20 @@ static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)

		/* deactivate handle */
		data->handle = handle;

		/*
		* Guard against a parallel DEACTIVATE command before the DF_FLUSH
		* command has completed.
		*/
		mutex_lock(&sev_deactivate_lock);

		sev_guest_deactivate(data, NULL);

		wbinvd_on_all_cpus();
		sev_guest_df_flush(NULL);

		mutex_unlock(&sev_deactivate_lock);

		kfree(data);

		decommission = kzalloc(sizeof(*decommission), GFP_KERNEL);
		@@ -6318,9 +6329,18 @@ static int sev_bind_asid(struct kvm kvm, unsigned int handle, int error)
		int asid = sev_get_asid(kvm);
		int ret;

		/*
		* Guard against a DEACTIVATE command before the DF_FLUSH command
		* has completed.
		*/
		mutex_lock(&sev_deactivate_lock);

		wbinvd_on_all_cpus();

		ret = sev_guest_df_flush(error);

		mutex_unlock(&sev_deactivate_lock);

		if (ret)
		return ret;

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