On Thu, Jan 05, 2023, Kees Cook wrote: > Zero-length arrays are deprecated[1]. Replace struct kvm_nested_state's > "data" union 0-length arrays with flexible arrays. (How are the > sizes of these arrays verified?) It's not really interpreted as an array, it's a mandatory single-entry "array". if (copy_from_user(vmcs12, user_vmx_nested_state->vmcs12, sizeof(*vmcs12))) return -EFAULT; > Detected with GCC 13, using -fstrict-flex-arrays=3: > > arch/x86/kvm/svm/nested.c: In function 'svm_get_nested_state': > arch/x86/kvm/svm/nested.c:1536:17: error: array subscript 0 is outside array bounds of 'struct kvm_svm_nested_state_data[0]' [-Werror=array-bounds=] > 1536 | &user_kvm_nested_state->data.svm[0]; > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > In file included from include/uapi/linux/kvm.h:15, > from include/linux/kvm_host.h:40, > from arch/x86/kvm/svm/nested.c:18: > arch/x86/include/uapi/asm/kvm.h:511:50: note: while referencing 'svm' > 511 | struct kvm_svm_nested_state_data svm[0]; > | ^~~ > > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays > > Cc: Sean Christopherson <seanjc@xxxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Borislav Petkov <bp@xxxxxxxxx> > Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx> > Cc: x86@xxxxxxxxxx > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > Cc: kvm@xxxxxxxxxxxxxxx > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- Nit on the comment aside, Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx> > arch/x86/include/uapi/asm/kvm.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h > index e48deab8901d..8ec3dfd641b0 100644 > --- a/arch/x86/include/uapi/asm/kvm.h > +++ b/arch/x86/include/uapi/asm/kvm.h > @@ -502,13 +502,13 @@ struct kvm_nested_state { > } hdr; > > /* > - * Define data region as 0 bytes to preserve backwards-compatability > + * Define union of flexible arrays to preserve backwards-compatability I think I'd actually prefer the "as 0 bytes" comment. The important part is that the size of "data" be zero, how that happens is immaterial. > * to old definition of kvm_nested_state in order to avoid changing > * KVM_{GET,PUT}_NESTED_STATE ioctl values. > */ > union { > - struct kvm_vmx_nested_state_data vmx[0]; > - struct kvm_svm_nested_state_data svm[0]; > + __DECLARE_FLEX_ARRAY(struct kvm_vmx_nested_state_data, vmx); > + __DECLARE_FLEX_ARRAY(struct kvm_svm_nested_state_data, svm); > } data; > }; > > -- > 2.34.1 >
