From fadbfc38dde26d31e901c3c85cf01332cb6a2224 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Tue, 14 Jul 2020 10:44:49 -0500 Subject: [PATCH] hpilo: Replace one-element array with flexible-array member MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit There is a regular need in the kernel to provide a way to declare having a dynamically sized set of trailing elements in a structure. Kernel code should always use “flexible array members”[1] for these cases. The older style of one-element or zero-length arrays should no longer be used[2]. For this particular case, it is important to notice that the cachelines change from 7 to 6 after the flexible-array conversion: $ pahole -C 'fifo' drivers/misc/hpilo.o struct fifo { u64 nrents; /* 0 8 */ u64 imask; /* 8 8 */ u64 merge; /* 16 8 */ u64 reset; /* 24 8 */ u8 pad_0[96]; /* 32 96 */ /* --- cacheline 2 boundary (128 bytes) --- */ u64 head; /* 128 8 */ u8 pad_1[120]; /* 136 120 */ /* --- cacheline 4 boundary (256 bytes) --- */ u64 tail; /* 256 8 */ u8 pad_2[120]; /* 264 120 */ /* --- cacheline 6 boundary (384 bytes) --- */ u64 fifobar[1]; /* 384 8 */ /* size: 392, cachelines: 7, members: 10 */ /* last cacheline: 8 bytes */ }; $ pahole -C 'fifo' drivers/misc/hpilo.o struct fifo { u64 nrents; /* 0 8 */ u64 imask; /* 8 8 */ u64 merge; /* 16 8 */ u64 reset; /* 24 8 */ u8 pad_0[96]; /* 32 96 */ /* --- cacheline 2 boundary (128 bytes) --- */ u64 head; /* 128 8 */ u8 pad_1[120]; /* 136 120 */ /* --- cacheline 4 boundary (256 bytes) --- */ u64 tail; /* 256 8 */ u8 pad_2[120]; /* 264 120 */ /* --- cacheline 6 boundary (384 bytes) --- */ u64 fifobar[]; /* 384 0 */ /* size: 384, cachelines: 6, members: 10 */ }; Lastly, remove unnecessary parentheses in fifo_sz() and fix the following checkpatch.pl warning for the whole fifo structure: WARNING: please, no spaces at the start of a line [1] https://en.wikipedia.org/wiki/Flexible_array_member [2] https://github.com/KSPP/linux/issues/79 Tested-by: kernel test robot Link: https://github.com/GustavoARSilva/linux-hardening/blob/master/cii/kernel-ci/hpilo-20200714.md Signed-off-by: Gustavo A. R. Silva Link: https://lore.kernel.org/r/20200714154449.GA26153@embeddedor Signed-off-by: Greg Kroah-Hartman --- drivers/misc/hpilo.c | 2 +- drivers/misc/hpilo.h | 22 +++++++++++----------- 2 files changed, 12 insertions(+), 12 deletions(-) diff --git a/drivers/misc/hpilo.c b/drivers/misc/hpilo.c index 927309b..10c9756 100644 --- a/drivers/misc/hpilo.c +++ b/drivers/misc/hpilo.c @@ -207,7 +207,7 @@ static void ctrl_setup(struct ccb *ccb, int nr_desc, int l2desc_sz) static inline int fifo_sz(int nr_entry) { /* size of a fifo is determined by the number of entries it contains */ - return (nr_entry * sizeof(u64)) + FIFOHANDLESIZE; + return nr_entry * sizeof(u64) + FIFOHANDLESIZE; } static void fifo_setup(void *base_addr, int nr_entry) diff --git a/drivers/misc/hpilo.h b/drivers/misc/hpilo.h index 1aa433a..f69ff64 100644 --- a/drivers/misc/hpilo.h +++ b/drivers/misc/hpilo.h @@ -160,23 +160,23 @@ struct ccb_data { #define ILO_START_ALIGN 4096 #define ILO_CACHE_SZ 128 struct fifo { - u64 nrents; /* user requested number of fifo entries */ - u64 imask; /* mask to extract valid fifo index */ - u64 merge; /* O/C bits to merge in during enqueue operation */ - u64 reset; /* set to non-zero when the target device resets */ - u8 pad_0[ILO_CACHE_SZ - (sizeof(u64) * 4)]; + u64 nrents; /* user requested number of fifo entries */ + u64 imask; /* mask to extract valid fifo index */ + u64 merge; /* O/C bits to merge in during enqueue operation */ + u64 reset; /* set to non-zero when the target device resets */ + u8 pad_0[ILO_CACHE_SZ - (sizeof(u64) * 4)]; - u64 head; - u8 pad_1[ILO_CACHE_SZ - (sizeof(u64))]; + u64 head; + u8 pad_1[ILO_CACHE_SZ - (sizeof(u64))]; - u64 tail; - u8 pad_2[ILO_CACHE_SZ - (sizeof(u64))]; + u64 tail; + u8 pad_2[ILO_CACHE_SZ - (sizeof(u64))]; - u64 fifobar[1]; + u64 fifobar[]; }; /* convert between struct fifo, and the fifobar, which is saved in the ccb */ -#define FIFOHANDLESIZE (sizeof(struct fifo) - sizeof(u64)) +#define FIFOHANDLESIZE (sizeof(struct fifo)) #define FIFOBARTOHANDLE(_fifo) \ ((struct fifo *)(((char *)(_fifo)) - FIFOHANDLESIZE)) -- 2.7.4