| Message ID | 20230105190548.never.323-kees@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Commit | 6e22a6282c67c17188aa9c22627467abd8566b3d |
| Headers | show |
| Series | KVM: x86: Replace 0-length arrays with flexible arrays | expand |
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@google.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org> > Cc: x86@kernel.org > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: kvm@vger.kernel.org > Signed-off-by: Kees Cook <keescook@chromium.org> > --- Nit on the comment aside, Reviewed-by: Sean Christopherson <seanjc@google.com> > 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 >
On Mon, Jan 09, 2023 at 05:30:48PM +0000, Sean Christopherson wrote: > 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; If it's mandatory, why is it [0] instead of just a single struct? i.e. why is it not: union { struct kvm_vmx_nested_state_data vmx; struct kvm_svm_nested_state_data svm; }; > > > 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@google.com> > > Cc: Paolo Bonzini <pbonzini@redhat.com> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: Ingo Molnar <mingo@redhat.com> > > Cc: Borislav Petkov <bp@alien8.de> > > Cc: Dave Hansen <dave.hansen@linux.intel.com> > > Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org> > > Cc: x86@kernel.org > > Cc: "H. Peter Anvin" <hpa@zytor.com> > > Cc: kvm@vger.kernel.org > > Signed-off-by: Kees Cook <keescook@chromium.org> > > --- > > Nit on the comment aside, > > Reviewed-by: Sean Christopherson <seanjc@google.com> > > > 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. Okay, I'll drop this part. > > > * 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 > >
On Mon, Jan 09, 2023 at 05:30:48PM +0000, Sean Christopherson wrote: > 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". [...] > > > > /* > > - * 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. Oh, dur, I can read the comment. :) It has to stay the old size -- this was a way to add an optional extra struct to the end. Got it!
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 * 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; };
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?) 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@google.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org> Cc: x86@kernel.org Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: kvm@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/x86/include/uapi/asm/kvm.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)