Re: [Qemu-devel] [PATCH for-1.4 v2] target-i386: kvm: prevent buffer overflow if -cpu foo, [x]level is too big

["Andreas Färber" <afaerber@suse.de>]

Am 28.01.2013 12:49, schrieb Igor Mammedov:
> Stack corruption may occur if too big 'level' or 'xlevel' values passed
> on command line with KVM enabled, due to limited size of cpuid_data
> in kvm_arch_init_vcpu().
> 
> reproduces with:
>  qemu -enable-kvm -cpu qemu64,level=4294967295
> or
>  qemu -enable-kvm -cpu qemu64,xlevel=4294967295
> 
> Check if there is space in cpuid_data before passing it to cpu_x86_cpuid()
> or abort() if there is not space.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>

Reviewed-by: Andreas Färber <afaerber@suse.de>

CC'ing Gleb and KVM list.

Andreas

> ---
>   * v2:
>     * use macro instead of const int max_cpuid_entries to fix build breakage
>       in C99 mode. Suggested-By: Laszlo Ersek <lersek@redhat.com>
>     * compare with array index instead of address of the last element
>           Sugested-By: Marcelo Tosatti <mtosatti@redhat.com>
> 
> ---
>  target-i386/kvm.c |   25 ++++++++++++++++++++++++-
>  1 files changed, 24 insertions(+), 1 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 3acff40..4ecb728 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -411,11 +411,12 @@ static void cpu_update_state(void *opaque, int running, RunState state)
>      }
>  }
>  
> +#define KVM_MAX_CPUID_ENTRIES  100
>  int kvm_arch_init_vcpu(CPUState *cs)
>  {
>      struct {
>          struct kvm_cpuid2 cpuid;
> -        struct kvm_cpuid_entry2 entries[100];
> +        struct kvm_cpuid_entry2 entries[KVM_MAX_CPUID_ENTRIES];
>      } QEMU_PACKED cpuid_data;
>      X86CPU *cpu = X86_CPU(cs);
>      CPUX86State *env = &cpu->env;
> @@ -502,6 +503,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      cpu_x86_cpuid(env, 0, 0, &limit, &unused, &unused, &unused);
>  
>      for (i = 0; i <= limit; i++) {
> +        if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
> +            fprintf(stderr, "unsupported level value: 0x%x\n", limit);
> +            abort();
> +        }
>          c = &cpuid_data.entries[cpuid_i++];
>  
>          switch (i) {
> @@ -516,6 +521,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
>              times = c->eax & 0xff;
>  
>              for (j = 1; j < times; ++j) {
> +                if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
> +                    fprintf(stderr, "cpuid_data is full, no space for "
> +                            "cpuid(eax:2):eax & 0xf = 0x%x\n", times);
> +                    abort();
> +                }
>                  c = &cpuid_data.entries[cpuid_i++];
>                  c->function = i;
>                  c->flags = KVM_CPUID_FLAG_STATEFUL_FUNC;
> @@ -544,6 +554,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
>                  if (i == 0xd && c->eax == 0) {
>                      continue;
>                  }
> +                if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
> +                    fprintf(stderr, "cpuid_data is full, no space for "
> +                            "cpuid(eax:0x%x,ecx:0x%x)\n", i, j);
> +                    abort();
> +                }
>                  c = &cpuid_data.entries[cpuid_i++];
>              }
>              break;
> @@ -557,6 +572,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      cpu_x86_cpuid(env, 0x80000000, 0, &limit, &unused, &unused, &unused);
>  
>      for (i = 0x80000000; i <= limit; i++) {
> +        if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
> +            fprintf(stderr, "unsupported xlevel value: 0x%x\n", limit);
> +            abort();
> +        }
>          c = &cpuid_data.entries[cpuid_i++];
>  
>          c->function = i;
> @@ -569,6 +588,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          cpu_x86_cpuid(env, 0xC0000000, 0, &limit, &unused, &unused, &unused);
>  
>          for (i = 0xC0000000; i <= limit; i++) {
> +            if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
> +                fprintf(stderr, "unsupported xlevel2 value: 0x%x\n", limit);
> +                abort();
> +            }
>              c = &cpuid_data.entries[cpuid_i++];
>  
>              c->function = i;
> 


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