[PATCH v3 0/2][next] clk: socfpga: Fix undefined behavior bug and add bounds-checking coverage

[PATCH v3 0/2][next] clk: socfpga: Fix undefined behavior bug and add bounds-checking coverage

[Gustavo A. R. Silva]

This series aims to fix an undefined behavior bug in
`struct stratix10_clock_data` and add bounds-checking
coverage at run-time for flexible-array member `hws`
in `struct clk_hw_onecell_data` when accessed throught
`struct stratix10_clock_data`.

Changes in v3:
 - None, really. Just Cc linux-clk@vger.kernel.org this time.

Changes in v2:
 - Mention -Wflex-array-member-not-at-end in the changelog text.
 - Link: https://lore.kernel.org/linux-hardening/cover.1697493574.git.gustavoars@kernel.org/

v1:
 - Link: https://lore.kernel.org/linux-hardening/cover.1697059539.git.gustavoars@kernel.org/

Gustavo A. R. Silva (2):
  clk: socfpga: Fix undefined behavior bug in struct
    stratix10_clock_data
  clk: socfpga: agilex: Add bounds-checking coverage for struct
    stratix10_clock_data

 drivers/clk/socfpga/clk-agilex.c    | 12 ++++++------
 drivers/clk/socfpga/clk-s10.c       |  6 +++---
 drivers/clk/socfpga/stratix10-clk.h |  4 +++-
 3 files changed, 12 insertions(+), 10 deletions(-)

-- 
2.34.1

[PATCH v3 1/2][next] clk: socfpga: Fix undefined behavior bug in struct stratix10_clock_data

[Gustavo A. R. Silva]

`struct clk_hw_onecell_data` is a flexible structure, which means that
it contains flexible-array member at the bottom, in this case array
`hws`:

include/linux/clk-provider.h:
1380 struct clk_hw_onecell_data {
1381         unsigned int num;
1382         struct clk_hw *hws[] __counted_by(num);
1383 };

This could potentially lead to an overwrite of the objects following
`clk_data` in `struct stratix10_clock_data`, in this case
`void __iomem *base;` at run-time:

drivers/clk/socfpga/stratix10-clk.h:
  9 struct stratix10_clock_data {
 10         struct clk_hw_onecell_data      clk_data;
 11         void __iomem            *base;
 12 };

There are currently three different places where memory is allocated for
`struct stratix10_clock_data`, including the flex-array `hws` in
`struct clk_hw_onecell_data`:

drivers/clk/socfpga/clk-agilex.c:
469         clk_data = devm_kzalloc(dev, struct_size(clk_data, clk_data.hws,
470                                 num_clks), GFP_KERNEL);

drivers/clk/socfpga/clk-agilex.c:
509         clk_data = devm_kzalloc(dev, struct_size(clk_data, clk_data.hws,
510                                 num_clks), GFP_KERNEL);

drivers/clk/socfpga/clk-s10.c:
400         clk_data = devm_kzalloc(dev, struct_size(clk_data, clk_data.hws,
401                                                  num_clks), GFP_KERNEL);

I'll use just one of them to describe the issue. See below.

Notice that a total of 440 bytes are allocated for flexible-array member
`hws` at line 469:

include/dt-bindings/clock/agilex-clock.h:
 70 #define AGILEX_NUM_CLKS	55

drivers/clk/socfpga/clk-agilex.c:
459         struct stratix10_clock_data *clk_data;
460         void __iomem *base;
...
466
467         num_clks = AGILEX_NUM_CLKS;
468
469         clk_data = devm_kzalloc(dev, struct_size(clk_data, clk_data.hws,
470                                 num_clks), GFP_KERNEL);

`struct_size(clk_data, clk_data.hws, num_clks)`	above translates to
sizeof(struct stratix10_clock_data) + sizeof(struct clk_hw *) * 55 ==
16 + 8 * 55 == 16 + 440
		    ^^^
		     |
	allocated bytes for flex-array `hws`

474         for (i = 0; i < num_clks; i++)
475                 clk_data->clk_data.hws[i] = ERR_PTR(-ENOENT);
476
477         clk_data->base = base;

and then some data is written into both `hws` and `base` objects.

Fix this by placing the declaration of object `clk_data` at the end of
`struct stratix10_clock_data`. Also, add a comment to make it clear
that this object must always be last in the structure.

-Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
ready to enable it globally.

Fixes: ba7e258425ac ("clk: socfpga: Convert to s10/agilex/n5x to use clk_hw")
Cc: stable@vger.kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v3:
 - None, really. Just Cc linux-clk@vger.kernel.org this time.

Changes in v2:
 - Mention -Wflex-array-member-not-at-end in the changelog text.
 - Link: https://lore.kernel.org/linux-hardening/bb2ae50abf622d4b6fda1a326ce830627356ab7c.1697493574.git.gustavoars@kernel.org/

v1:
 - Link: https://lore.kernel.org/linux-hardening/5dd8483177dc8cd91d021170b6717f2e570bab03.1697059539.git.gustavoars@kernel.org/

 drivers/clk/socfpga/stratix10-clk.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/socfpga/stratix10-clk.h b/drivers/clk/socfpga/stratix10-clk.h
index 75234e0783e1..83fe4eb3133c 100644
--- a/drivers/clk/socfpga/stratix10-clk.h
+++ b/drivers/clk/socfpga/stratix10-clk.h
@@ -7,8 +7,10 @@
 #define	__STRATIX10_CLK_H
 
 struct stratix10_clock_data {
-	struct clk_hw_onecell_data	clk_data;
 	void __iomem		*base;
+
+	/* Must be last */
+	struct clk_hw_onecell_data	clk_data;
 };
 
 struct stratix10_pll_clock {
-- 
2.34.1

[PATCH v3 2/2][next] clk: socfpga: agilex: Add bounds-checking coverage for struct stratix10_clock_data

[Gustavo A. R. Silva]

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.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v3:
 - None, really. Just Cc linux-clk@vger.kernel.org this time.

Changes in v2:
 - None.
 - Link: https://lore.kernel.org/linux-hardening/f531ae35ef434b62f48534c67ad3b1013bff0536.1697493574.git.gustavoars@kernel.org/

v1:
 - Link: https://lore.kernel.org/linux-hardening/fd4cd8503316d536e1a84fa2ae5bdefdd4b24afe.1697059539.git.gustavoars@kernel.org/

 drivers/clk/socfpga/clk-agilex.c | 12 ++++++------
 drivers/clk/socfpga/clk-s10.c    |  6 +++---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/clk/socfpga/clk-agilex.c b/drivers/clk/socfpga/clk-agilex.c
index 6b65a74aefa6..8dd94f64756b 100644
--- a/drivers/clk/socfpga/clk-agilex.c
+++ b/drivers/clk/socfpga/clk-agilex.c
@@ -471,12 +471,12 @@ static int agilex_clkmgr_init(struct platform_device *pdev)
 	if (!clk_data)
 		return -ENOMEM;
 
+	clk_data->clk_data.num = num_clks;
+	clk_data->base = base;
+
 	for (i = 0; i < num_clks; i++)
 		clk_data->clk_data.hws[i] = ERR_PTR(-ENOENT);
 
-	clk_data->base = base;
-	clk_data->clk_data.num = num_clks;
-
 	agilex_clk_register_pll(agilex_pll_clks, ARRAY_SIZE(agilex_pll_clks), clk_data);
 
 	agilex_clk_register_c_perip(agilex_main_perip_c_clks,
@@ -511,12 +511,12 @@ static int n5x_clkmgr_init(struct platform_device *pdev)
 	if (!clk_data)
 		return -ENOMEM;
 
-	for (i = 0; i < num_clks; i++)
-		clk_data->clk_data.hws[i] = ERR_PTR(-ENOENT);
-
 	clk_data->base = base;
 	clk_data->clk_data.num = num_clks;
 
+	for (i = 0; i < num_clks; i++)
+		clk_data->clk_data.hws[i] = ERR_PTR(-ENOENT);
+
 	n5x_clk_register_pll(agilex_pll_clks, ARRAY_SIZE(agilex_pll_clks), clk_data);
 
 	n5x_clk_register_c_perip(n5x_main_perip_c_clks,
diff --git a/drivers/clk/socfpga/clk-s10.c b/drivers/clk/socfpga/clk-s10.c
index 3752bd9c103c..b4bf4e2d38e1 100644
--- a/drivers/clk/socfpga/clk-s10.c
+++ b/drivers/clk/socfpga/clk-s10.c
@@ -402,12 +402,12 @@ static int s10_clkmgr_init(struct platform_device *pdev)
 	if (!clk_data)
 		return -ENOMEM;
 
-	for (i = 0; i < num_clks; i++)
-		clk_data->clk_data.hws[i] = ERR_PTR(-ENOENT);
-
 	clk_data->base = base;
 	clk_data->clk_data.num = num_clks;
 
+	for (i = 0; i < num_clks; i++)
+		clk_data->clk_data.hws[i] = ERR_PTR(-ENOENT);
+
 	s10_clk_register_pll(s10_pll_clks, ARRAY_SIZE(s10_pll_clks), clk_data);
 
 	s10_clk_register_c_perip(s10_main_perip_c_clks,
-- 
2.34.1