From fddcca5107051adf9e4481d2a79ae0616577fd2c Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Mon, 29 Feb 2016 13:20:28 +0100 Subject: [PATCH] mtd: avoid stack overflow in MTD CFI code When map_word gets too large, we use a lot of kernel stack, and for MTD_MAP_BANK_WIDTH_32, this means we use more than the recommended 1024 bytes in a number of functions: drivers/mtd/chips/cfi_cmdset_0020.c: In function 'cfi_staa_write_buffers': drivers/mtd/chips/cfi_cmdset_0020.c:651:1: warning: the frame size of 1336 bytes is larger than 1024 bytes [-Wframe-larger-than=] drivers/mtd/chips/cfi_cmdset_0020.c: In function 'cfi_staa_erase_varsize': drivers/mtd/chips/cfi_cmdset_0020.c:972:1: warning: the frame size of 1208 bytes is larger than 1024 bytes [-Wframe-larger-than=] drivers/mtd/chips/cfi_cmdset_0001.c: In function 'do_write_buffer': drivers/mtd/chips/cfi_cmdset_0001.c:1835:1: warning: the frame size of 1240 bytes is larger than 1024 bytes [-Wframe-larger-than=] This can be avoided if all operations on the map word are done indirectly and the stack gets reused between the calls. We can mostly achieve this by selecting MTD_COMPLEX_MAPPINGS whenever MTD_MAP_BANK_WIDTH_32 is set, but for the case that no other bank width is enabled, we also need to use a non-constant map_bankwidth() to convince the compiler to use less stack. Signed-off-by: Arnd Bergmann [Brian: this patch mostly achieves its goal by forcing MTD_COMPLEX_MAPPINGS (and the accompanying indirection) for 256-bit mappings; the rest of the change is mostly a wash, though it helps reduce stack size slightly. If we really care about supporting 256-bit mappings though, we should consider rewriting some of this code to avoid keeping and assigning so many 256-bit objects on the stack.] Signed-off-by: Brian Norris --- drivers/mtd/chips/Kconfig | 1 + include/linux/mtd/map.h | 19 +++++++------------ 2 files changed, 8 insertions(+), 12 deletions(-) diff --git a/drivers/mtd/chips/Kconfig b/drivers/mtd/chips/Kconfig index 3b3dabce58de..bbfa1f129266 100644 --- a/drivers/mtd/chips/Kconfig +++ b/drivers/mtd/chips/Kconfig @@ -115,6 +115,7 @@ config MTD_MAP_BANK_WIDTH_16 config MTD_MAP_BANK_WIDTH_32 bool "Support 256-bit buswidth" if MTD_CFI_GEOMETRY + select MTD_COMPLEX_MAPPINGS if HAS_IOMEM default n help If you wish to support CFI devices on a physical bus which is diff --git a/include/linux/mtd/map.h b/include/linux/mtd/map.h index 5e0eb7ccabd4..3aa56e3104bb 100644 --- a/include/linux/mtd/map.h +++ b/include/linux/mtd/map.h @@ -122,18 +122,13 @@ #endif #ifdef CONFIG_MTD_MAP_BANK_WIDTH_32 -# ifdef map_bankwidth -# undef map_bankwidth -# define map_bankwidth(map) ((map)->bankwidth) -# undef map_bankwidth_is_large -# define map_bankwidth_is_large(map) (map_bankwidth(map) > BITS_PER_LONG/8) -# undef map_words -# define map_words(map) map_calc_words(map) -# else -# define map_bankwidth(map) 32 -# define map_bankwidth_is_large(map) (1) -# define map_words(map) map_calc_words(map) -# endif +/* always use indirect access for 256-bit to preserve kernel stack */ +# undef map_bankwidth +# define map_bankwidth(map) ((map)->bankwidth) +# undef map_bankwidth_is_large +# define map_bankwidth_is_large(map) (map_bankwidth(map) > BITS_PER_LONG/8) +# undef map_words +# define map_words(map) map_calc_words(map) #define map_bankwidth_is_32(map) (map_bankwidth(map) == 32) #undef MAX_MAP_BANKWIDTH #define MAX_MAP_BANKWIDTH 32