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 --- kernel/bpf/core.c | 4 ++-- kernel/locking/test-ww_mutex.c | 4 ++-- kernel/time/clocksource.c | 2 +- 3 files changed, 5 insertions(+), 5 deletions(-) (limited to 'kernel') diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 59cf4dc728a5..53c6c98bda7b 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1032,7 +1032,7 @@ bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr, hdr->size = size; hole = min_t(unsigned int, size - (proglen + sizeof(*hdr)), PAGE_SIZE - sizeof(*hdr)); - start = (get_random_int() % hole) & ~(alignment - 1); + start = prandom_u32_max(hole) & ~(alignment - 1); /* Leave a random number of instructions before BPF code. */ *image_ptr = &hdr->image[start]; @@ -1094,7 +1094,7 @@ bpf_jit_binary_pack_alloc(unsigned int proglen, u8 **image_ptr, hole = min_t(unsigned int, size - (proglen + sizeof(*ro_header)), BPF_PROG_CHUNK_SIZE - sizeof(*ro_header)); - start = (get_random_int() % hole) & ~(alignment - 1); + start = prandom_u32_max(hole) & ~(alignment - 1); *image_ptr = &ro_header->image[start]; *rw_image = &(*rw_header)->image[start]; diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c index 353004155d65..43efb2a04160 100644 --- a/kernel/locking/test-ww_mutex.c +++ b/kernel/locking/test-ww_mutex.c @@ -399,7 +399,7 @@ static int *get_random_order(int count) order[n] = n; for (n = count - 1; n > 1; n--) { - r = get_random_int() % (n + 1); + r = prandom_u32_max(n + 1); if (r != n) { tmp = order[n]; order[n] = order[r]; @@ -538,7 +538,7 @@ static void stress_one_work(struct work_struct *work) { struct stress *stress = container_of(work, typeof(*stress), work); const int nlocks = stress->nlocks; - struct ww_mutex *lock = stress->locks + (get_random_int() % nlocks); + struct ww_mutex *lock = stress->locks + prandom_u32_max(nlocks); int err; do { diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index cee5da1e54c4..8058bec87ace 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -310,7 +310,7 @@ static void clocksource_verify_choose_cpus(void) * CPUs that are currently online. */ for (i = 1; i < n; i++) { - cpu = prandom_u32() % nr_cpu_ids; + cpu = prandom_u32_max(nr_cpu_ids); cpu = cpumask_next(cpu - 1, cpu_online_mask); if (cpu >= nr_cpu_ids) cpu = cpumask_first(cpu_online_mask); -- cgit v1.2.3