linux-hardening - Re: [PATCH v2] KVM: x86: Replace 0-length arrays with flexible arrays

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Message-ID: <202301191518.3DB46101E9@keescook>
Date:   Thu, 19 Jan 2023 15:20:24 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Replace 0-length arrays with flexible arrays

On Thu, Jan 19, 2023 at 08:48:52PM +0000, Sean Christopherson wrote:
> On Wed, 18 Jan 2023 11:59:09 -0800, 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?) 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];
> >       |                                                  ^~~
> > 
> > [...]
> 
> Applied to kvm-x86 misc, thanks!  Based on the linux-next complaint, I assume
> you (temporarily?) applied this to your tree as well.  Holler if I've confused
> you :-)

Thanks! I've removed it from my tree.

-- 
Kees Cook