linux-hardening - Re: [PATCH][next] xen: privcmd: Replace zero-length array with flex-array member and use __counted

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Message-ID: <f7f37c51-d378-4b63-a23b-0447d8688f95@suse.com>
Date: Fri, 17 Nov 2023 08:24:44 +0100
From: Juergen Gross <jgross@...e.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] xen: privcmd: Replace zero-length array with
 flex-array member and use __counted_by

On 16.11.23 19:54, Gustavo A. R. Silva wrote:
> Fake flexible arrays (zero-length and one-element arrays) are deprecated,
> and should be replaced by flexible-array members. So, replace
> zero-length array with a flexible-array member in `struct
> privcmd_kernel_ioreq`.
> 
> Also annotate array `ports` with `__counted_by()` to prepare for the
> coming implementation by GCC and Clang of the `__counted_by` attribute.
> Flexible array members annotated with `__counted_by` can have their
> accesses bounds-checked at run-time via `CONFIG_UBSAN_BOUNDS` (for array
> indexing) and `CONFIG_FORTIFY_SOURCE` (for strcpy/memcpy-family functions).
> 
> This fixes multiple -Warray-bounds warnings:
> drivers/xen/privcmd.c:1239:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1240:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1241:30: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1245:33: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> drivers/xen/privcmd.c:1258:67: warning: array subscript i is outside array bounds of 'struct ioreq_port[0]' [-Warray-bounds=]
> 
> This results in no differences in binary output.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen


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