Re: [Qemu-devel] [PATCH for 1.7] kvm: Fix uninitialized cpuid_data

[Gleb Natapov]

On Wed, Nov 06, 2013 at 10:35:27PM +0100, Stefan Weil wrote:
> This error was reported by valgrind when running qemu-system-x86_64
> with kvm:
> 
> ==975== Conditional jump or move depends on uninitialised value(s)
> ==975==    at 0x521C38: cpuid_find_entry (kvm.c:176)
> ==975==    by 0x5235BA: kvm_arch_init_vcpu (kvm.c:686)
> ==975==    by 0x4D5175: kvm_init_vcpu (kvm-all.c:267)
> ==975==    by 0x45035B: qemu_kvm_cpu_thread_fn (cpus.c:858)
> ==975==    by 0xD361E0D: start_thread (pthread_create.c:311)
> ==975==    by 0xD65E9EC: clone (clone.S:113)
> ==975==  Uninitialised value was created by a stack allocation
> ==975==    at 0x5226E4: kvm_arch_init_vcpu (kvm.c:446)
> 
> Instead of adding more memset calls for parts of cpuid_data, the existing
> calls were removed and cpuid_data is now initialized completely in one
> call.
> 
> Signed-off-by: Stefan Weil <address@hidden>
Applied, thanks.

> ---
> 
> I did not check whether older versions also need this fix.
> 
> Stefan W.
> 
>  target-i386/kvm.c |    9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 749aa09..3ffd3e0 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -456,11 +456,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      uint32_t signature[3];
>      int r;
>  
> +    memset(&cpuid_data, 0, sizeof(cpuid_data));
> +
>      cpuid_i = 0;
>  
>      /* Paravirtualization CPUIDs */
>      c = &cpuid_data.entries[cpuid_i++];
> -    memset(c, 0, sizeof(*c));
>      c->function = KVM_CPUID_SIGNATURE;
>      if (!hyperv_enabled(cpu)) {
>          memcpy(signature, "KVMKVMKVM\0\0\0", 12);
> @@ -474,7 +475,6 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      c->edx = signature[2];
>  
>      c = &cpuid_data.entries[cpuid_i++];
> -    memset(c, 0, sizeof(*c));
>      c->function = KVM_CPUID_FEATURES;
>      c->eax = env->features[FEAT_KVM];
>  
> @@ -483,13 +483,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          c->eax = signature[0];
>  
>          c = &cpuid_data.entries[cpuid_i++];
> -        memset(c, 0, sizeof(*c));
>          c->function = HYPERV_CPUID_VERSION;
>          c->eax = 0x00001bbc;
>          c->ebx = 0x00060001;
>  
>          c = &cpuid_data.entries[cpuid_i++];
> -        memset(c, 0, sizeof(*c));
>          c->function = HYPERV_CPUID_FEATURES;
>          if (cpu->hyperv_relaxed_timing) {
>              c->eax |= HV_X64_MSR_HYPERCALL_AVAILABLE;
> @@ -500,7 +498,6 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          }
>  
>          c = &cpuid_data.entries[cpuid_i++];
> -        memset(c, 0, sizeof(*c));
>          c->function = HYPERV_CPUID_ENLIGHTMENT_INFO;
>          if (cpu->hyperv_relaxed_timing) {
>              c->eax |= HV_X64_RELAXED_TIMING_RECOMMENDED;
> @@ -511,13 +508,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          c->ebx = cpu->hyperv_spinlock_attempts;
>  
>          c = &cpuid_data.entries[cpuid_i++];
> -        memset(c, 0, sizeof(*c));
>          c->function = HYPERV_CPUID_IMPLEMENT_LIMITS;
>          c->eax = 0x40;
>          c->ebx = 0x40;
>  
>          c = &cpuid_data.entries[cpuid_i++];
> -        memset(c, 0, sizeof(*c));
>          c->function = KVM_CPUID_SIGNATURE_NEXT;
>          memcpy(signature, "KVMKVMKVM\0\0\0", 12);
>          c->eax = 0;
> -- 
> 1.7.10.4

--
                        Gleb.