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

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Message-ID: <675633f7ae9893371d35b238f06fd02a3acffebb.1697076650.git.gustavoars@kernel.org>
Date:   Wed, 11 Oct 2023 20:18:45 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
Cc:     Kees Cook <keescook@...omium.org>, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.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@...nel.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