Hi Gustavo A. R. Silva, Thanks for your patch!
> -----Original Message----- > From: Gustavo A. R. Silva <[email protected]> > Sent: Thursday, October 12, 2023 11:18 AM > To: Michael Turquette <[email protected]>; Stephen Boyd > <[email protected]>; iwamatsu nobuhiro(岩松 信洋 ○ＤＩＴＣ□ＤＩＴ○Ｏ > ＳＴ) <[email protected]> > Cc: Kees Cook <[email protected]>; [email protected]; > [email protected]; [email protected]; Gustavo A. > R. Silva <[email protected]>; [email protected] > Subject: [PATCH 1/2][next] clk: visconti: Fix undefined behavior bug in struct > visconti_pll_provider > > `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 visconti_pll_provider`, in this case `struct device_node *node;`, at > run-time: > > drivers/clk/visconti/pll.h: > 16 struct visconti_pll_provider { > 17 void __iomem *reg_base; > 18 struct clk_hw_onecell_data clk_data; > 19 struct device_node *node; > 20 }; > > Notice that a total of 56 bytes are allocated for flexible-array `hws` at > line 328. > See below: > > include/dt-bindings/clock/toshiba,tmpv770x.h: > 14 #define TMPV770X_NR_PLL 7 > > drivers/clk/visconti/pll-tmpv770x.c: > 69 ctx = visconti_init_pll(np, reg_base, TMPV770X_NR_PLL); > > drivers/clk/visconti/pll.c: > 321 struct visconti_pll_provider * __init visconti_init_pll(struct device_node > *np, > 322 void __iomem > *base, > 323 unsigned long > nr_plls) > 324 { > 325 struct visconti_pll_provider *ctx; > ... > 328 ctx = kzalloc(struct_size(ctx, clk_data.hws, nr_plls), > GFP_KERNEL); > > `struct_size(ctx, clk_data.hws, nr_plls)` above translates to sizeof(struct > visconti_pll_provider) + sizeof(struct clk_hw *) * 7 == > 24 + 8 * 7 == 24 + 56 > ^^^^ > | > allocated bytes for flex array `hws` > > $ pahole -C visconti_pll_provider drivers/clk/visconti/pll.o struct > visconti_pll_provider { > void * reg_base; /* 0 8 */ > struct clk_hw_onecell_data clk_data; /* 8 8 */ > struct device_node * node; /* 16 8 */ > > /* size: 24, cachelines: 1, members: 3 */ > /* last cacheline: 24 bytes */ > }; > > And then, after the allocation, some data is written into all members of > `struct > visconti_pll_provider`: > > 332 for (i = 0; i < nr_plls; ++i) > 333 ctx->clk_data.hws[i] = ERR_PTR(-ENOENT); > 334 > 335 ctx->node = np; > 336 ctx->reg_base = base; > 337 ctx->clk_data.num = nr_plls; > > Fix all these by placing the declaration of object `clk_data` at the end of > `struct > visconti_pll_provider`. Also, add a comment to make it clear that this object > must always be last in the structure, and prevent this bug from being > introduced again in the future. > > Fixes: b4cbe606dc36 ("clk: visconti: Add support common clock driver and > reset driver") > Cc: [email protected] > Signed-off-by: Gustavo A. R. Silva <[email protected]> Acked-by: Nobuhiro Iwamatsu <[email protected]> Best regards, Nobuhiro
