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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id eo22sm11175964ejc.0.2021.04.06.07.21.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Apr 2021 07:21:09 -0700 (PDT) From: Vitaly Kuznetsov To: Emanuele Giuseppe Esposito , kvm@vger.kernel.org Cc: Paolo Bonzini , Jonathan Corbet , Sean Christopherson , Emanuele Giuseppe Esposito , Jim Mattson , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Shuah Khan , Alexander Graf , Andrew Jones , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v3 1/4] KVM: x86: Fix a spurious -E2BIG in KVM_GET_EMULATED_CPUID In-Reply-To: <20210406082642.20115-2-eesposit@redhat.com> References: <20210406082642.20115-1-eesposit@redhat.com> <20210406082642.20115-2-eesposit@redhat.com> Date: Tue, 06 Apr 2021 16:21:08 +0200 Message-ID: <87k0pfcx4b.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Emanuele Giuseppe Esposito writes: > When retrieving emulated CPUID entries, check for an insufficient array > size if and only if KVM is actually inserting an entry. > If userspace has a priori knowledge of the exact array size, > KVM_GET_EMULATED_CPUID will incorrectly fail due to effectively requiring > an extra, unused entry. > > Signed-off-by: Emanuele Giuseppe Esposito > --- > arch/x86/kvm/cpuid.c | 33 ++++++++++++++++----------------- > 1 file changed, 16 insertions(+), 17 deletions(-) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 6bd2f8b830e4..27059ddf9f0a 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -567,34 +567,33 @@ static struct kvm_cpuid_entry2 *do_host_cpuid(struct kvm_cpuid_array *array, > > static int __do_cpuid_func_emulated(struct kvm_cpuid_array *array, u32 func) > { > - struct kvm_cpuid_entry2 *entry; > - > - if (array->nent >= array->maxnent) > - return -E2BIG; > + struct kvm_cpuid_entry2 entry; > > - entry = &array->entries[array->nent]; > - entry->function = func; > - entry->index = 0; > - entry->flags = 0; > + memset(&entry, 0, sizeof(entry)); > + entry.function = func; > > switch (func) { > case 0: > - entry->eax = 7; > - ++array->nent; > + entry.eax = 7; > break; > case 1: > - entry->ecx = F(MOVBE); > - ++array->nent; > + entry.ecx = F(MOVBE); > break; > case 7: > - entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX; > - entry->eax = 0; > - entry->ecx = F(RDPID); > - ++array->nent; > - default: > + entry.flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX; > + entry.eax = 0; Nitpick: there's no need to set entry.eax = 0 as the whole structure was zeroed. Also, '|=' for flags could be just '='. > + entry.ecx = F(RDPID); > break; > + default: > + goto out; > } > > + if (array->nent >= array->maxnent) > + return -E2BIG; > + > + memcpy(&array->entries[array->nent++], &entry, sizeof(entry)); > + > +out: > return 0; > } Reviewed-by: Vitaly Kuznetsov -- Vitaly