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@kernel.org>
---
 drivers/clk/visconti/pll.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/visconti/pll.c b/drivers/clk/visconti/pll.c
index 1f3234f22667..e9cd80e085dc 100644
--- a/drivers/clk/visconti/pll.c
+++ b/drivers/clk/visconti/pll.c
@@ -329,12 +329,12 @@ struct visconti_pll_provider * __init visconti_init_pll(struct device_node *np,
 	if (!ctx)
 		return ERR_PTR(-ENOMEM);
 
-	for (i = 0; i < nr_plls; ++i)
-		ctx->clk_data.hws[i] = ERR_PTR(-ENOENT);
-
 	ctx->node = np;
 	ctx->reg_base = base;
 	ctx->clk_data.num = nr_plls;
 
+	for (i = 0; i < nr_plls; ++i)
+		ctx->clk_data.hws[i] = ERR_PTR(-ENOENT);
+
 	return ctx;
 }
-- 
2.34.1

Hi Gustavo A. R. Silva,

Thanks for your patch!

> -----Original Message-----
> From: Gustavo A. R. Silva <gustavoars@kernel.org>
> Sent: Thursday, October 12, 2023 11:19 AM
> To: Michael Turquette <mturquette@baylibre.com>; Stephen Boyd
> <sboyd@kernel.org>; iwamatsu nobuhiro(岩松 信洋 ○ＤＩＴＣ□ＤＩＴ○Ｏ
> ＳＴ) <nobuhiro1.iwamatsu@toshiba.co.jp>
> Cc: Kees Cook <keescook@chromium.org>; linux-clk@vger.kernel.org;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; Gustavo A.
> R. Silva <gustavoars@kernel.org>; linux-hardening@vger.kernel.org
> 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@kernel.org>

Acked-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>

Best regards,
  Nobuhiro

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@kernel.org>

Looks good; thanks!

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

-- 
Kees Cook