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Date:   Mon, 10 Oct 2022 17:06:10 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Böhmwalder 
        <christoph.boehmwalder@...bit.com>, Christoph Hellwig <hch@....de>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Daniel Borkmann <daniel@...earbox.net>,
        Dave Airlie <airlied@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Westphal <fw@...len.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Helge Deller <deller@....de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Huacai Chen <chenhuacai@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        Jan Kara <jack@...e.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Jens Axboe <axboe@...nel.dk>,
        Johannes Berg <johannes@...solutions.net>,
        Jonathan Corbet <corbet@....net>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        KP Singh <kpsingh@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Weinberger <richard@....at>,
        Russell King <linux@...linux.org.uk>,
        Theodore Ts'o <tytso@....edu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Thomas Graf <tgraf@...g.ch>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        WANG Xuerui <kernel@...0n.name>, Will Deacon <will@...nel.org>,
        Yury Norov <yury.norov@...il.com>,
        dri-devel@...ts.freedesktop.org, kasan-dev@...glegroups.com,
        kernel-janitors@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-mm@...ck.org,
        linux-mmc@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-nvme@...ts.infradead.org, linux-parisc@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-usb@...r.kernel.org,
        linux-wireless@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        loongarch@...ts.linux.dev, netdev@...r.kernel.org,
        sparclinux@...r.kernel.org, x86@...nel.org
Subject: [PATCH v6 4/7] treewide: use get_random_{u8,u16}() when possible, part 2

Rather than truncate a 32-bit value to a 16-bit value or an 8-bit value,
simply use the get_random_{u8,u16}() functions, which are faster than
wasting the additional bytes from a 32-bit value. This was done by hand,
identifying all of the places where one of the random integer functions
was used in a non-32-bit context.

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Yury Norov <yury.norov@...il.com>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 arch/s390/kernel/process.c     | 2 +-
 drivers/mtd/nand/raw/nandsim.c | 2 +-
 lib/test_vmalloc.c             | 2 +-
 net/rds/bind.c                 | 2 +-
 net/sched/sch_sfb.c            | 2 +-
 5 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 5ec78555dd2e..42af4b3aa02b 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -230,7 +230,7 @@ unsigned long arch_align_stack(unsigned long sp)
 
 static inline unsigned long brk_rnd(void)
 {
-	return (get_random_int() & BRK_RND_MASK) << PAGE_SHIFT;
+	return (get_random_u16() & BRK_RND_MASK) << PAGE_SHIFT;
 }
 
 unsigned long arch_randomize_brk(struct mm_struct *mm)
diff --git a/drivers/mtd/nand/raw/nandsim.c b/drivers/mtd/nand/raw/nandsim.c
index 50bcf745e816..d211939c8bdd 100644
--- a/drivers/mtd/nand/raw/nandsim.c
+++ b/drivers/mtd/nand/raw/nandsim.c
@@ -1402,7 +1402,7 @@ static int ns_do_read_error(struct nandsim *ns, int num)
 
 static void ns_do_bit_flips(struct nandsim *ns, int num)
 {
-	if (bitflips && prandom_u32() < (1 << 22)) {
+	if (bitflips && get_random_u16() < (1 << 6)) {
 		int flips = 1;
 		if (bitflips > 1)
 			flips = prandom_u32_max(bitflips) + 1;
diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index a26bbbf20e62..cf7780572f5b 100644
--- a/lib/test_vmalloc.c
+++ b/lib/test_vmalloc.c
@@ -80,7 +80,7 @@ static int random_size_align_alloc_test(void)
 	int i;
 
 	for (i = 0; i < test_loop_count; i++) {
-		rnd = prandom_u32();
+		rnd = get_random_u8();
 
 		/*
 		 * Maximum 1024 pages, if PAGE_SIZE is 4096.
diff --git a/net/rds/bind.c b/net/rds/bind.c
index 5b5fb4ca8d3e..97a29172a8ee 100644
--- a/net/rds/bind.c
+++ b/net/rds/bind.c
@@ -104,7 +104,7 @@ static int rds_add_bound(struct rds_sock *rs, const struct in6_addr *addr,
 			return -EINVAL;
 		last = rover;
 	} else {
-		rover = max_t(u16, prandom_u32(), 2);
+		rover = max_t(u16, get_random_u16(), 2);
 		last = rover - 1;
 	}
 
diff --git a/net/sched/sch_sfb.c b/net/sched/sch_sfb.c
index e2389fa3cff8..0366a1a029a9 100644
--- a/net/sched/sch_sfb.c
+++ b/net/sched/sch_sfb.c
@@ -379,7 +379,7 @@ static int sfb_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		goto enqueue;
 	}
 
-	r = prandom_u32() & SFB_MAX_PROB;
+	r = get_random_u16() & SFB_MAX_PROB;
 
 	if (unlikely(r < p_min)) {
 		if (unlikely(p_min > SFB_MAX_PROB / 2)) {
-- 
2.37.3

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