arch/x86/include/uapi/asm/kvm.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
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(-)
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;
};
--
2.34.1On 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". [...] > > > > /* > > - * 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! -- Kees Cook
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
> >
--
Kees Cook
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