| Message ID | 20210114003708.3798992-2-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: SVM: Misc SEV cleanups | expand |
On 1/13/21 6:36 PM, Sean Christopherson wrote: > Zero out the array of VMCB pointers so that pre_sev_run() won't see > garbage when querying the array to detect when an SEV ASID is being > associated with a new VMCB. In practice, reading random values is all > but guaranteed to be benign as a false negative (which is extremely > unlikely on its own) can only happen on CPU0 on the first VMRUN and would > only cause KVM to skip the ASID flush. For anything bad to happen, a > previous instance of KVM would have to exit without flushing the ASID, > _and_ KVM would have to not flush the ASID at any time while building the > new SEV guest. > > Cc: Borislav Petkov <bp@suse.de> > Cc: Tom Lendacky <thomas.lendacky@amd.com> > Cc: Brijesh Singh <brijesh.singh@amd.com> > Fixes: 70cd94e60c73 ("KVM: SVM: VMRUN should use associated ASID when SEV is enabled") > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/svm/svm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 7ef171790d02..ccf52c5531fb 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -573,7 +573,7 @@ static int svm_cpu_init(int cpu) > if (svm_sev_enabled()) { > sd->sev_vmcbs = kmalloc_array(max_sev_asid + 1, > sizeof(void *), > - GFP_KERNEL); > + GFP_KERNEL | __GFP_ZERO); Alternatively, this call could just be changed to kcalloc(). Either way, Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> > if (!sd->sev_vmcbs) > goto free_save_area; > } >
On Thu, Jan 14, 2021, Tom Lendacky wrote: > On 1/13/21 6:36 PM, Sean Christopherson wrote: > > Zero out the array of VMCB pointers so that pre_sev_run() won't see > > garbage when querying the array to detect when an SEV ASID is being > > associated with a new VMCB. In practice, reading random values is all > > but guaranteed to be benign as a false negative (which is extremely > > unlikely on its own) can only happen on CPU0 on the first VMRUN and would > > only cause KVM to skip the ASID flush. For anything bad to happen, a > > previous instance of KVM would have to exit without flushing the ASID, > > _and_ KVM would have to not flush the ASID at any time while building the > > new SEV guest. > > > > Cc: Borislav Petkov <bp@suse.de> > > Cc: Tom Lendacky <thomas.lendacky@amd.com> > > Cc: Brijesh Singh <brijesh.singh@amd.com> > > Fixes: 70cd94e60c73 ("KVM: SVM: VMRUN should use associated ASID when SEV is enabled") > > Signed-off-by: Sean Christopherson <seanjc@google.com> > > --- > > arch/x86/kvm/svm/svm.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > > index 7ef171790d02..ccf52c5531fb 100644 > > --- a/arch/x86/kvm/svm/svm.c > > +++ b/arch/x86/kvm/svm/svm.c > > @@ -573,7 +573,7 @@ static int svm_cpu_init(int cpu) > > if (svm_sev_enabled()) { > > sd->sev_vmcbs = kmalloc_array(max_sev_asid + 1, > > sizeof(void *), > > - GFP_KERNEL); > > + GFP_KERNEL | __GFP_ZERO); > > Alternatively, this call could just be changed to kcalloc(). Agreed, kcalloc() is a better option. I'll do that in v3.
On 1/13/21 6:36 PM, Sean Christopherson wrote: > Zero out the array of VMCB pointers so that pre_sev_run() won't see > garbage when querying the array to detect when an SEV ASID is being > associated with a new VMCB. In practice, reading random values is all > but guaranteed to be benign as a false negative (which is extremely > unlikely on its own) can only happen on CPU0 on the first VMRUN and would > only cause KVM to skip the ASID flush. For anything bad to happen, a > previous instance of KVM would have to exit without flushing the ASID, > _and_ KVM would have to not flush the ASID at any time while building the > new SEV guest. > > Cc: Borislav Petkov <bp@suse.de> > Cc: Tom Lendacky <thomas.lendacky@amd.com> > Cc: Brijesh Singh <brijesh.singh@amd.com> > Fixes: 70cd94e60c73 ("KVM: SVM: VMRUN should use associated ASID when SEV is enabled") > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/svm/svm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 7ef171790d02..ccf52c5531fb 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -573,7 +573,7 @@ static int svm_cpu_init(int cpu) > if (svm_sev_enabled()) { > sd->sev_vmcbs = kmalloc_array(max_sev_asid + 1, > sizeof(void *), > - GFP_KERNEL); > + GFP_KERNEL | __GFP_ZERO); > if (!sd->sev_vmcbs) > goto free_save_area; > } Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 7ef171790d02..ccf52c5531fb 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -573,7 +573,7 @@ static int svm_cpu_init(int cpu) if (svm_sev_enabled()) { sd->sev_vmcbs = kmalloc_array(max_sev_asid + 1, sizeof(void *), - GFP_KERNEL); + GFP_KERNEL | __GFP_ZERO); if (!sd->sev_vmcbs) goto free_save_area; }
Zero out the array of VMCB pointers so that pre_sev_run() won't see garbage when querying the array to detect when an SEV ASID is being associated with a new VMCB. In practice, reading random values is all but guaranteed to be benign as a false negative (which is extremely unlikely on its own) can only happen on CPU0 on the first VMRUN and would only cause KVM to skip the ASID flush. For anything bad to happen, a previous instance of KVM would have to exit without flushing the ASID, _and_ KVM would have to not flush the ASID at any time while building the new SEV guest. Cc: Borislav Petkov <bp@suse.de> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Brijesh Singh <brijesh.singh@amd.com> Fixes: 70cd94e60c73 ("KVM: SVM: VMRUN should use associated ASID when SEV is enabled") Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/svm/svm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)