| Message ID | 20210713160957.3269017-5-ehabkost@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [PULL,01/11] i386: clarify 'hv-passthrough' behavior | expand |
On Tue, 13 Jul 2021 at 17:19, Eduardo Habkost <ehabkost@redhat.com> wrote: > > From: Vitaly Kuznetsov <vkuznets@redhat.com> > > To make Hyper-V features appear in e.g. QMP query-cpu-model-expansion we > need to expand and set the corresponding CPUID leaves early. Modify > x86_cpu_get_supported_feature_word() to call newly intoduced Hyper-V > specific kvm_hv_get_supported_cpuid() instead of > kvm_arch_get_supported_cpuid(). We can't use kvm_arch_get_supported_cpuid() > as Hyper-V specific CPUID leaves intersect with KVM's. > > Note, early expansion will only happen when KVM supports system wide > KVM_GET_SUPPORTED_HV_CPUID ioctl (KVM_CAP_SYS_HYPERV_CPUID). > > Reviewed-by: Eduardo Habkost <ehabkost@redhat.com> > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> > Message-Id: <20210608120817.1325125-6-vkuznets@redhat.com> > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> Hi; Coverity reports an issue in this code (CID 1458243): > -static bool hyperv_expand_features(CPUState *cs, Error **errp) > +bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp) > { > - X86CPU *cpu = X86_CPU(cs); > + CPUState *cs = CPU(cpu); > > if (!hyperv_enabled(cpu)) > return true; > > + /* > + * When kvm_hyperv_expand_features is called at CPU feature expansion > + * time per-CPU kvm_state is not available yet so we can only proceed > + * when KVM_CAP_SYS_HYPERV_CPUID is supported. > + */ > + if (!cs->kvm_state && > + !kvm_check_extension(kvm_state, KVM_CAP_SYS_HYPERV_CPUID)) > + return true; Here we check whether cs->kvm_state is NULL, but even if it is NULL we can still continue execution further through the function. Later in the function we call hv_cpuid_get_host(), which in turn can call get_supported_hv_cpuid_legacy(), which can dereference cs->kvm_state without checking it. So either the check on cs->kvm_state above is unnecessary, or we need to handle it being NULL in some way other than falling through. Side note: this change isn't in line with our coding style, which requires braces around the body of the if(). thanks -- PMM
Peter Maydell <peter.maydell@linaro.org> writes: > On Tue, 13 Jul 2021 at 17:19, Eduardo Habkost <ehabkost@redhat.com> wrote: >> >> From: Vitaly Kuznetsov <vkuznets@redhat.com> >> >> To make Hyper-V features appear in e.g. QMP query-cpu-model-expansion we >> need to expand and set the corresponding CPUID leaves early. Modify >> x86_cpu_get_supported_feature_word() to call newly intoduced Hyper-V >> specific kvm_hv_get_supported_cpuid() instead of >> kvm_arch_get_supported_cpuid(). We can't use kvm_arch_get_supported_cpuid() >> as Hyper-V specific CPUID leaves intersect with KVM's. >> >> Note, early expansion will only happen when KVM supports system wide >> KVM_GET_SUPPORTED_HV_CPUID ioctl (KVM_CAP_SYS_HYPERV_CPUID). >> >> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> >> Message-Id: <20210608120817.1325125-6-vkuznets@redhat.com> >> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> > > Hi; Coverity reports an issue in this code (CID 1458243): > >> -static bool hyperv_expand_features(CPUState *cs, Error **errp) >> +bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp) >> { >> - X86CPU *cpu = X86_CPU(cs); >> + CPUState *cs = CPU(cpu); >> >> if (!hyperv_enabled(cpu)) >> return true; >> >> + /* >> + * When kvm_hyperv_expand_features is called at CPU feature expansion >> + * time per-CPU kvm_state is not available yet so we can only proceed >> + * when KVM_CAP_SYS_HYPERV_CPUID is supported. >> + */ >> + if (!cs->kvm_state && >> + !kvm_check_extension(kvm_state, KVM_CAP_SYS_HYPERV_CPUID)) >> + return true; > > Here we check whether cs->kvm_state is NULL, but even if it is > NULL we can still continue execution further through the function. > > Later in the function we call hv_cpuid_get_host(), which in turn > can call get_supported_hv_cpuid_legacy(), which can dereference > cs->kvm_state without checking it. get_supported_hv_cpuid_legacy() is only called when KVM_CAP_HYPERV_CPUID is not supported and this is not possible with KVM_CAP_SYS_HYPERV_CPUID. Coverity, of course, can't know that. > > So either the check on cs->kvm_state above is unnecessary, or we > need to handle it being NULL in some way other than falling through. It seems an assert(cs) before calling get_supported_hv_cpuid_legacy() (with a proper comment) should do the job. > > Side note: this change isn't in line with our coding style, which > requires braces around the body of the if(). My bad, will fix.
diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h index dc725083891..54667b35f09 100644 --- a/target/i386/kvm/kvm_i386.h +++ b/target/i386/kvm/kvm_i386.h @@ -47,6 +47,7 @@ bool kvm_has_x2apic_api(void); bool kvm_has_waitpkg(void); bool kvm_hv_vpindex_settable(void); +bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp); uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address); diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 5f595a0d7e2..46befde3876 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -5974,6 +5974,10 @@ void x86_cpu_expand_features(X86CPU *cpu, Error **errp) if (env->cpuid_xlevel2 == UINT32_MAX) { env->cpuid_xlevel2 = env->cpuid_min_xlevel2; } + + if (kvm_enabled()) { + kvm_hyperv_expand_features(cpu, errp); + } } /* diff --git a/target/i386/kvm/kvm-stub.c b/target/i386/kvm/kvm-stub.c index 92f49121b8f..f6e7e4466e1 100644 --- a/target/i386/kvm/kvm-stub.c +++ b/target/i386/kvm/kvm-stub.c @@ -39,3 +39,8 @@ bool kvm_hv_vpindex_settable(void) { return false; } + +bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp) +{ + abort(); +} diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index ef127762bca..556815db13d 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -1220,13 +1220,22 @@ static uint32_t hv_build_cpuid_leaf(CPUState *cs, uint32_t func, int reg) * of 'hv_passthrough' mode and fills the environment with all supported * Hyper-V features. */ -static bool hyperv_expand_features(CPUState *cs, Error **errp) +bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp) { - X86CPU *cpu = X86_CPU(cs); + CPUState *cs = CPU(cpu); if (!hyperv_enabled(cpu)) return true; + /* + * When kvm_hyperv_expand_features is called at CPU feature expansion + * time per-CPU kvm_state is not available yet so we can only proceed + * when KVM_CAP_SYS_HYPERV_CPUID is supported. + */ + if (!cs->kvm_state && + !kvm_check_extension(kvm_state, KVM_CAP_SYS_HYPERV_CPUID)) + return true; + if (cpu->hyperv_passthrough) { cpu->hyperv_vendor_id[0] = hv_cpuid_get_host(cs, HV_CPUID_VENDOR_AND_MAX_FUNCTIONS, R_EBX); @@ -1593,8 +1602,15 @@ int kvm_arch_init_vcpu(CPUState *cs) env->apic_bus_freq = KVM_APIC_BUS_FREQUENCY; - /* Paravirtualization CPUIDs */ - if (!hyperv_expand_features(cs, &local_err)) { + /* + * kvm_hyperv_expand_features() is called here for the second time in case + * KVM_CAP_SYS_HYPERV_CPUID is not supported. While we can't possibly handle + * 'query-cpu-model-expansion' in this case as we don't have a KVM vCPU to + * check which Hyper-V enlightenments are supported and which are not, we + * can still proceed and check/expand Hyper-V enlightenments here so legacy + * behavior is preserved. + */ + if (!kvm_hyperv_expand_features(cpu, &local_err)) { error_report_err(local_err); return -ENOSYS; }