From 81895a65ec63ee1daec3255dc1a06675d2fbe915 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 5 Oct 2022 16:43:38 +0200 Subject: treewide: use prandom_u32_max() when possible, part 1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Rather than incurring a division or requesting too many random bytes for the given range, use the prandom_u32_max() function, which only takes the minimum required bytes from the RNG and avoids divisions. This was done mechanically with this coccinelle script: @basic@ expression E; type T; identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32"; typedef u64; @@ ( - ((T)get_random_u32() % (E)) + prandom_u32_max(E) | - ((T)get_random_u32() & ((E) - 1)) + prandom_u32_max(E * XXX_MAKE_SURE_E_IS_POW2) | - ((u64)(E) * get_random_u32() >> 32) + prandom_u32_max(E) | - ((T)get_random_u32() & ~PAGE_MASK) + prandom_u32_max(PAGE_SIZE) ) @multi_line@ identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32"; identifier RAND; expression E; @@ - RAND = get_random_u32(); ... when != RAND - RAND %= (E); + RAND = prandom_u32_max(E); // Find a potential literal @literal_mask@ expression LITERAL; type T; identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32"; position p; @@ ((T)get_random_u32()@p & (LITERAL)) // Add one to the literal. @script:python add_one@ literal << literal_mask.LITERAL; RESULT; @@ value = None if literal.startswith('0x'): value = int(literal, 16) elif literal[0] in '123456789': value = int(literal, 10) if value is None: print("I don't know how to handle %s" % (literal)) cocci.include_match(False) elif value == 2**32 - 1 or value == 2**31 - 1 or value == 2**24 - 1 or value == 2**16 - 1 or value == 2**8 - 1: print("Skipping 0x%x for cleanup elsewhere" % (value)) cocci.include_match(False) elif value & (value + 1) != 0: print("Skipping 0x%x because it's not a power of two minus one" % (value)) cocci.include_match(False) elif literal.startswith('0x'): coccinelle.RESULT = cocci.make_expr("0x%x" % (value + 1)) else: coccinelle.RESULT = cocci.make_expr("%d" % (value + 1)) // Replace the literal mask with the calculated result. @plus_one@ expression literal_mask.LITERAL; position literal_mask.p; expression add_one.RESULT; identifier FUNC; @@ - (FUNC()@p & (LITERAL)) + prandom_u32_max(RESULT) @collapse_ret@ type T; identifier VAR; expression E; @@ { - T VAR; - VAR = (E); - return VAR; + return E; } @drop_var@ type T; identifier VAR; @@ { - T VAR; ... when != VAR } Reviewed-by: Greg Kroah-Hartman Reviewed-by: Kees Cook Reviewed-by: Yury Norov Reviewed-by: KP Singh Reviewed-by: Jan Kara # for ext4 and sbitmap Reviewed-by: Christoph Böhmwalder # for drbd Acked-by: Jakub Kicinski Acked-by: Heiko Carstens # for s390 Acked-by: Ulf Hansson # for mmc Acked-by: Darrick J. Wong # for xfs Signed-off-by: Jason A. Donenfeld --- fs/f2fs/gc.c | 2 +- fs/f2fs/segment.c | 8 ++++---- 2 files changed, 5 insertions(+), 5 deletions(-) (limited to 'fs/f2fs') diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c index d36bcb23ccfe..4546e01b2ee0 100644 --- a/fs/f2fs/gc.c +++ b/fs/f2fs/gc.c @@ -282,7 +282,7 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type, /* let's select beginning hot/small space first in no_heap mode*/ if (f2fs_need_rand_seg(sbi)) - p->offset = prandom_u32() % (MAIN_SECS(sbi) * sbi->segs_per_sec); + p->offset = prandom_u32_max(MAIN_SECS(sbi) * sbi->segs_per_sec); else if (test_opt(sbi, NOHEAP) && (type == CURSEG_HOT_DATA || IS_NODESEG(type))) p->offset = 0; diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c index 289bcb7ca300..acf3d3fa4363 100644 --- a/fs/f2fs/segment.c +++ b/fs/f2fs/segment.c @@ -2534,7 +2534,7 @@ static unsigned int __get_next_segno(struct f2fs_sb_info *sbi, int type) sanity_check_seg_type(sbi, seg_type); if (f2fs_need_rand_seg(sbi)) - return prandom_u32() % (MAIN_SECS(sbi) * sbi->segs_per_sec); + return prandom_u32_max(MAIN_SECS(sbi) * sbi->segs_per_sec); /* if segs_per_sec is large than 1, we need to keep original policy. */ if (__is_large_section(sbi)) @@ -2588,7 +2588,7 @@ static void new_curseg(struct f2fs_sb_info *sbi, int type, bool new_sec) curseg->alloc_type = LFS; if (F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_BLK) curseg->fragment_remained_chunk = - prandom_u32() % sbi->max_fragment_chunk + 1; + prandom_u32_max(sbi->max_fragment_chunk) + 1; } static int __next_free_blkoff(struct f2fs_sb_info *sbi, @@ -2625,9 +2625,9 @@ static void __refresh_next_blkoff(struct f2fs_sb_info *sbi, /* To allocate block chunks in different sizes, use random number */ if (--seg->fragment_remained_chunk <= 0) { seg->fragment_remained_chunk = - prandom_u32() % sbi->max_fragment_chunk + 1; + prandom_u32_max(sbi->max_fragment_chunk) + 1; seg->next_blkoff += - prandom_u32() % sbi->max_fragment_hole + 1; + prandom_u32_max(sbi->max_fragment_hole) + 1; } } } -- cgit