linux-kernel - Re: [PATCH 2/2][next] clk: socfpga: agilex: Add bounds-checking coverage for struct stratix10_clock

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Date:   Wed, 11 Oct 2023 14:41:03 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Dinh Nguyen <dinguyen@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/2][next] clk: socfpga: agilex: Add bounds-checking
 coverage for struct stratix10_clock_data

On Wed, Oct 11, 2023 at 03:35:26PM -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 case `num`, is updated
> before the first access to the flex-array member, in this case array `hws`.
> 
> 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 sstratix10_clock_data`:
> 
> drivers/clk/socfpga/stratix10-clk.h:
>   9 struct stratix10_clock_data {
>  10         void __iomem            *base;
>  11 
>  12         /* Must be last */
>  13         struct clk_hw_onecell_data      clk_data;
>  14 };
> 
> Hence, we need to move the assignments to `clk_data->clk_data.num` after
> allocations for `struct stratix10_clock_data` and before accessing the
> flexible array `clk_data->clk_data.hws`. And, as assignments for both
> `clk_data->clk_data.num` and `clk_data->base` are originally adjacent to
> each other, relocate both assignments together.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Yeah, ew. That's super tricky. Nice find.

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

-- 
Kees Cook