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Date: Thu, 16 Nov 2023 15:18:00 -0600 From: "Gustavo A. R. Silva" <gustavo@...eddedor.com> To: Kees Cook <keescook@...omium.org>, "Gustavo A. R. Silva" <gustavoars@...nel.org> Cc: Juergen Gross <jgross@...e.com>, Stefano Stabellini <sstabellini@...nel.org>, Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>, 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 11/16/23 15:08, Kees Cook wrote: > On Thu, Nov 16, 2023 at 12:54:59PM -0600, 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> > > Looks right to me. I can see the allocation: Yep, I always check for that; in particular, the 'counter' assignment. :) Do you want me to mention it in the changelog text? > > size = struct_size(kioreq, ports, ioeventfd->vcpus); > kioreq = kzalloc(size, GFP_KERNEL); > if (!kioreq) > return ERR_PTR(-ENOMEM); > > kioreq->dom = ioeventfd->dom; > kioreq->vcpus = ioeventfd->vcpus; > > > Reviewed-by: Kees Cook <keescook@...omium.org> Thanks! -- Gustavo
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