linux-kernel - Re: [PATCH][next] media: venus: hfi_cmds: Replace one-element array with flex-array member and use __counted

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Message-ID: <20240109124026.GA1012017@google.com>
Date: Tue, 9 Jan 2024 21:40:26 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Kees Cook <keescook@...omium.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
	Vikash Garodia <quic_vgarodia@...cinc.com>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	Andy Gross <agross@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] media: venus: hfi_cmds: Replace one-element array
 with flex-array member and use __counted_by

On (23/10/09 12:52), Kees Cook wrote:
> On Mon, Oct 09, 2023 at 12:42:05PM -0600, Gustavo A. R. Silva wrote:
> > Array `data` in `struct hfi_sfr` is being used as a fake flexible array
> > at run-time:
> > 
> > drivers/media/platform/qcom/venus/hfi_venus.c:
> > 1033         p = memchr(sfr->data, '\0', sfr->buf_size);
> > 1034         /*
> > 1035          * SFR isn't guaranteed to be NULL terminated since SYS_ERROR indicates
> > 1036          * that Venus is in the process of crashing.
> > 1037          */
> > 1038         if (!p)
> > 1039                 sfr->data[sfr->buf_size - 1] = '\0';
> > 1040
> > 1041         dev_err_ratelimited(dev, "SFR message from FW: %s\n", sfr->data);
> > 
> > Fake flexible arrays are deprecated, and should be replaced by
> > flexible-array members. So, replace one-element array with a
> > flexible-array member in `struct hfi_sfr`.
> > 
> > While there, also annotate array `data` 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 results in no differences in binary output.
> 
> Thanks for checking!

Sorry for shameless plug, a quick question: has any compiler implemented
support for counted_by() at this point?