[PATCH v3 01/13] clk: microchip: mpfs: fix clk_cfg array bounds violation

[Conor Dooley]

Unnoticed in current code, there is an array bounds violation present
during clock registration. This seems to fail gracefully in v6.0-rc1,
and life carrys on. While converting the driver to use standard clock
structs/ops, kernel panics were seen during boot when built with clang:

[    0.581754] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000b1
[    0.591520] Oops [#1]
[    0.594045] Modules linked in:
[    0.597435] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.0.0-rc1-00011-g8e1459cf4eca #1
[    0.606188] Hardware name: Microchip PolarFire-SoC Icicle Kit (DT)
[    0.613012] epc : __clk_register+0x4a6/0x85c
[    0.617759]  ra : __clk_register+0x49e/0x85c
[    0.622489] epc : ffffffff803faf7c ra : ffffffff803faf74 sp : ffffffc80400b720
[    0.630466]  gp : ffffffff810e93f8 tp : ffffffe77fe60000 t0 : ffffffe77ffb3800
[    0.638443]  t1 : 000000000000000a t2 : ffffffffffffffff s0 : ffffffc80400b7c0
[    0.646420]  s1 : 0000000000000001 a0 : 0000000000000001 a1 : 0000000000000000
[    0.654396]  a2 : 0000000000000001 a3 : 0000000000000000 a4 : 0000000000000000
[    0.662373]  a5 : ffffffff803a5810 a6 : 0000000200000022 a7 : 0000000000000006
[    0.670350]  s2 : ffffffff81099d48 s3 : ffffffff80d6e28e s4 : 0000000000000028
[    0.678327]  s5 : ffffffff810ed3c8 s6 : ffffffff810ed3d0 s7 : ffffffe77ffbc100
[    0.686304]  s8 : ffffffe77ffb1540 s9 : ffffffe77ffb1540 s10: 0000000000000008
[    0.694281]  s11: 0000000000000000 t3 : 00000000000000c6 t4 : 0000000000000007
[    0.702258]  t5 : ffffffff810c78c0 t6 : ffffffe77ff88cd0
[    0.708125] status: 0000000200000120 badaddr: 00000000000000b1 cause: 000000000000000d
[    0.716869] [<ffffffff803fb892>] devm_clk_hw_register+0x62/0xaa
[    0.723420] [<ffffffff80403412>] mpfs_clk_probe+0x1e0/0x244

It fails on "clk_periph_timer" - which uses a different parent, that it
tries to find using the macro:
\#define PARENT_CLK(PARENT) (&mpfs_cfg_clks[CLK_##PARENT].cfg.hw)

If parent is RTCREF, so the macro becomes: &mpfs_cfg_clks[33].cfg.hw
which is well beyond the end of the array. Amazingly, builds with GCC
11.1 see no problem here, booting correctly and hooking the parent up
etc. Builds with clang-15 do not, with the above panic.

Drop the macro for the RTCREF and use the array directly to avoid the
panic, using a newly added define that brings the index into the valid
range.

Fixes: 1c6a7ea32b8c ("clk: microchip: mpfs: add RTCREF clock control")
CC: Nathan Chancellor <nathan at kernel.org>
Signed-off-by: Conor Dooley <conor.dooley at microchip.com>
---
 drivers/clk/microchip/clk-mpfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/microchip/clk-mpfs.c b/drivers/clk/microchip/clk-mpfs.c
index 070c3b896559..9e41f07b3fa6 100644
--- a/drivers/clk/microchip/clk-mpfs.c
+++ b/drivers/clk/microchip/clk-mpfs.c
@@ -27,6 +27,8 @@
 #define MSSPLL_POSTDIV_WIDTH	0x07u
 #define MSSPLL_FIXED_DIV	4u
 
+#define RTCREF_OFFSET		(CLK_RTCREF - CLK_ENVM)
+
 struct mpfs_clock_data {
 	void __iomem *base;
 	void __iomem *msspll_base;
@@ -381,7 +383,8 @@ static struct mpfs_periph_hw_clock mpfs_periph_clks[] = {
 	CLK_PERIPH(CLK_MAC0, "clk_periph_mac0", PARENT_CLK(AHB), 1, 0),
 	CLK_PERIPH(CLK_MAC1, "clk_periph_mac1", PARENT_CLK(AHB), 2, 0),
 	CLK_PERIPH(CLK_MMC, "clk_periph_mmc", PARENT_CLK(AHB), 3, 0),
-	CLK_PERIPH(CLK_TIMER, "clk_periph_timer", PARENT_CLK(RTCREF), 4, 0),
+	CLK_PERIPH(CLK_TIMER, "clk_periph_timer",
+		   &mpfs_cfg_clks[CLK_RTCREF - RTCREF_OFFSET].hw, 4, 0),
 	CLK_PERIPH(CLK_MMUART0, "clk_periph_mmuart0", PARENT_CLK(AHB), 5, CLK_IS_CRITICAL),
 	CLK_PERIPH(CLK_MMUART1, "clk_periph_mmuart1", PARENT_CLK(AHB), 6, 0),
 	CLK_PERIPH(CLK_MMUART2, "clk_periph_mmuart2", PARENT_CLK(AHB), 7, 0),
-- 
2.36.1