linux-kernel - Re: [PATCH 2/2][next] clk: visconti: Add bounds-checking coverage for struct visconti_pll

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Message-ID: <202310120921.3F24CB2E@keescook>
Date:   Thu, 12 Oct 2023 09:21:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/2][next] clk: visconti: Add bounds-checking coverage
 for struct visconti_pll_provider

On Wed, Oct 11, 2023 at 08:18:45PM -0600, Gustavo A. R. Silva wrote:
> In order to gain the bounds-checking coverage that __counted_by provides
> to flexible-array members at run-time via CONFIG_UBSAN_BOUNDS (for array
> indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family functions),
> we must make sure that the counter member, in this particular case `num`,
> is updated before the first access to the flex-array member, in this
> particular case array `hws`. See below:
> 
> commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with
> __counted_by") introduced `__counted_by` for `struct clk_hw_onecell_data`
> together with changes to relocate some of assignments of counter `num`
> before `hws` is accessed:
> 
> include/linux/clk-provider.h:
> 1380 struct clk_hw_onecell_data {
> 1381         unsigned int num;
> 1382         struct clk_hw *hws[] __counted_by(num);
> 1383 };
> 
> However, this structure is used as a member in other structs, in this
> case in `struct visconti_pll_provider`:
> 
> drivers/clk/visconti/pll.h:
>  16 struct visconti_pll_provider {
>  17         void __iomem *reg_base;
>  18         struct device_node *node;
>  19 
>  20         /* Must be last */
>  21         struct clk_hw_onecell_data clk_data;
>  22 };
> 
> Hence, we need to move the assignments to `ctx->clk_data.num` after
> allocation for `struct visconti_pll_provider` and before accessing the
> flexible array `ctx->clk_data.hws`. And, as assignments for all members
> in `struct visconti_pll_provider` are originally adjacent to each other,
> relocate all assignments together, so we don't split up
> `ctx->clk_data.hws = nr_plls` from the rest. :)
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Looks good; thanks!

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook