| Message ID | 20220715114211.53175-2-yu.c.zhang@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Fix the #PF injection logic for smaller MAXPHYADDR in nested. | expand |
On Fri, Jul 15, 2022, Yu Zhang wrote: > kvm_fixup_and_inject_pf_error() was introduced to fixup the error code( > e.g., to add RSVD flag) and inject the #PF to the guest, when guest > MAXPHYADDR is smaller than the host one. > > When it comes to nested, L0 is expected to intercept and fix up the #PF > and then inject to L2 directly if > - L2.MAXPHYADDR < L0.MAXPHYADDR and > - L1 has no intention to intercept L2's #PF (e.g., L2 and L1 have the > same MAXPHYADDR value && L1 is using EPT for L2), > instead of constructing a #PF VM Exit to L1. Currently, with PFEC_MASK > and PFEC_MATCH both set to 0 in vmcs02, the interception and injection > may happen on all L2 #PFs. > > However, failing to initialize 'fault' in kvm_fixup_and_inject_pf_error() > may cause the fault.async_page_fault being NOT zeroed, and later the #PF > being treated as a nested async page fault, and then being injected to L1. > So just fix it by initialize the 'fault' value in the beginning. Ouch. > Fixes: 897861479c064 ("KVM: x86: Add helper functions for illegal GPA checking and page fault injection") > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216178 > Reported-by: Yang Lixiao <lixiao.yang@intel.com> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> > --- > arch/x86/kvm/x86.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 031678eff28e..3246b3c9dfb3 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -12983,7 +12983,7 @@ EXPORT_SYMBOL_GPL(kvm_spec_ctrl_test_value); > void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_code) > { > struct kvm_mmu *mmu = vcpu->arch.walk_mmu; > - struct x86_exception fault; > + struct x86_exception fault = {0}; > u64 access = error_code & > (PFERR_WRITE_MASK | PFERR_FETCH_MASK | PFERR_USER_MASK); As stupid as it may be to intentionally not fix the uninitialized data in a robust way, I'd actually prefer to manually clear fault.async_page_fault instead of zero-initializing the struct. Unlike a similar bug fix in commit 159e037d2e36 ("KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op()"), this code actually cares about async_page_fault being false as opposed to just being _initialized_. And if another field is added to struct x86_exception in the future, leaving the struct uninitialized means that if such a patch were to miss this case, running with various sanitizers should in theory be able to detect such a bug. I suspect no one has found this with syzkaller due to the need to opt into running with allow_smaller_maxphyaddr=1. diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index f389691d8c04..aeed737b55c2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12996,6 +12996,7 @@ void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_c fault.error_code = error_code; fault.nested_page_fault = false; fault.address = gva; + fault.async_page_fault = false; } vcpu->arch.walk_mmu->inject_page_fault(vcpu, &fault); }
On Fri, Jul 15, 2022 at 02:47:36PM +0000, Sean Christopherson wrote: > On Fri, Jul 15, 2022, Yu Zhang wrote: > > kvm_fixup_and_inject_pf_error() was introduced to fixup the error code( > > e.g., to add RSVD flag) and inject the #PF to the guest, when guest > > MAXPHYADDR is smaller than the host one. > > > > When it comes to nested, L0 is expected to intercept and fix up the #PF > > and then inject to L2 directly if > > - L2.MAXPHYADDR < L0.MAXPHYADDR and > > - L1 has no intention to intercept L2's #PF (e.g., L2 and L1 have the > > same MAXPHYADDR value && L1 is using EPT for L2), > > instead of constructing a #PF VM Exit to L1. Currently, with PFEC_MASK > > and PFEC_MATCH both set to 0 in vmcs02, the interception and injection > > may happen on all L2 #PFs. > > > > However, failing to initialize 'fault' in kvm_fixup_and_inject_pf_error() > > may cause the fault.async_page_fault being NOT zeroed, and later the #PF > > being treated as a nested async page fault, and then being injected to L1. > > So just fix it by initialize the 'fault' value in the beginning. > > Ouch. > > > Fixes: 897861479c064 ("KVM: x86: Add helper functions for illegal GPA checking and page fault injection") > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216178 > > Reported-by: Yang Lixiao <lixiao.yang@intel.com> > > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> > > --- > > arch/x86/kvm/x86.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index 031678eff28e..3246b3c9dfb3 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -12983,7 +12983,7 @@ EXPORT_SYMBOL_GPL(kvm_spec_ctrl_test_value); > > void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_code) > > { > > struct kvm_mmu *mmu = vcpu->arch.walk_mmu; > > - struct x86_exception fault; > > + struct x86_exception fault = {0}; > > u64 access = error_code & > > (PFERR_WRITE_MASK | PFERR_FETCH_MASK | PFERR_USER_MASK); > > As stupid as it may be to intentionally not fix the uninitialized data in a robust > way, I'd actually prefer to manually clear fault.async_page_fault instead of > zero-initializing the struct. Unlike a similar bug fix in commit 159e037d2e36 > ("KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op()"), > this code actually cares about async_page_fault being false as opposed to just > being _initialized_. > > And if another field is added to struct x86_exception in the future, leaving the > struct uninitialized means that if such a patch were to miss this case, running > with various sanitizers should in theory be able to detect such a bug. I suspect > no one has found this with syzkaller due to the need to opt into running with > allow_smaller_maxphyaddr=1. > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index f389691d8c04..aeed737b55c2 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -12996,6 +12996,7 @@ void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_c > fault.error_code = error_code; > fault.nested_page_fault = false; > fault.address = gva; > + fault.async_page_fault = false; > } > vcpu->arch.walk_mmu->inject_page_fault(vcpu, &fault); > } > Fair enough. Thanks! B.R. Yu
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 031678eff28e..3246b3c9dfb3 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12983,7 +12983,7 @@ EXPORT_SYMBOL_GPL(kvm_spec_ctrl_test_value); void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_code) { struct kvm_mmu *mmu = vcpu->arch.walk_mmu; - struct x86_exception fault; + struct x86_exception fault = {0}; u64 access = error_code & (PFERR_WRITE_MASK | PFERR_FETCH_MASK | PFERR_USER_MASK);
kvm_fixup_and_inject_pf_error() was introduced to fixup the error code( e.g., to add RSVD flag) and inject the #PF to the guest, when guest MAXPHYADDR is smaller than the host one. When it comes to nested, L0 is expected to intercept and fix up the #PF and then inject to L2 directly if - L2.MAXPHYADDR < L0.MAXPHYADDR and - L1 has no intention to intercept L2's #PF (e.g., L2 and L1 have the same MAXPHYADDR value && L1 is using EPT for L2), instead of constructing a #PF VM Exit to L1. Currently, with PFEC_MASK and PFEC_MATCH both set to 0 in vmcs02, the interception and injection may happen on all L2 #PFs. However, failing to initialize 'fault' in kvm_fixup_and_inject_pf_error() may cause the fault.async_page_fault being NOT zeroed, and later the #PF being treated as a nested async page fault, and then being injected to L1. So just fix it by initialize the 'fault' value in the beginning. Fixes: 897861479c064 ("KVM: x86: Add helper functions for illegal GPA checking and page fault injection") Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216178 Reported-by: Yang Lixiao <lixiao.yang@intel.com> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> --- arch/x86/kvm/x86.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)