RE: [PATCH 2/2][next] clk: visconti: Add bounds-checking coverage for struct visconti_pll_provider

[nobuhiro1.iwamatsu]

Hi Gustavo A. R. Silva,

Thanks for your patch!

> -----Original Message-----
> From: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> Sent: Thursday, October 12, 2023 11:19 AM
> To: Michael Turquette <mturquette@xxxxxxxxxxxx>; Stephen Boyd
> <sboyd@xxxxxxxxxx>; iwamatsu nobuhiro(岩松 信洋 ○ＤＩＴＣ□ＤＩＴ○Ｏ
> ＳＴ) <nobuhiro1.iwamatsu@xxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>; linux-clk@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Gustavo A.
> R. Silva <gustavoars@xxxxxxxxxx>; linux-hardening@xxxxxxxxxxxxxxx
> Subject: [PATCH 2/2][next] clk: visconti: Add bounds-checking coverage for
> struct visconti_pll_provider
> 
> 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@xxxxxxxxxx>

Acked-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@xxxxxxxxxxxxx>

Best regards,
  Nobuhiro