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Message-Id: <20160803233913.32511-2-jason@lakedaemon.net>
Date: Wed, 3 Aug 2016 23:39:07 +0000
From: Jason Cooper <jason@...edaemon.net>
To: Kees Cook <keescook@...omium.org>,
Michael Ellerman <mpe@...erman.id.au>,
"Roberts, William C" <william.c.roberts@...el.com>,
Yann Droneaud <ydroneaud@...eya.com>
Cc: "Linux-MM" <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening" <kernel-hardening@...ts.openwall.com>,
"Russell King - ARM Linux" <linux@....linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
"Theodore Ts'o" <tytso@....edu>,
Arnd Bergmann <arnd@...db.de>,
gregkh@...uxfoundation.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Ralf Baechle <ralf@...ux-mips.org>,
benh@...nel.crashing.org,
paulus@...ba.org,
"David S. Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
x86@...nel.org,
viro@...iv.linux.org.uk,
Nick Kralevich <nnk@...gle.com>,
Jeffrey Vander Stoep <jeffv@...gle.com>,
Daniel Cashman <dcashman@...roid.com>,
Jason Cooper <jason@...edaemon.net>
Subject: [PATCH v3 1/7] random: Simplify API for random address requests
To date, all callers of randomize_range() have set the length to 0, and
check for a zero return value. For the current callers, the only way
to get zero returned is if end <= start. Since they are all adding a
constant to the start address, this is unnecessary.
We can remove a bunch of needless checks by simplifying the API to do
just what everyone wants, return an address between [start, start +
range).
While we're here, s/get_random_int/get_random_long/. No current call
site is adversely affected by get_random_int(), since all current range
requests are < UINT_MAX. However, we should match caller expectations
to avoid coming up short (ha!) in the future.
All current callers to randomize_range() chose to use the start address
if randomize_range() failed. Therefore, we simplify things by just
returning the start address on error.
randomize_range() will be removed once all callers have been converted
over to randomize_addr().
Signed-off-by: Jason Cooper <jason@...edaemon.net>
---
Changes from v2:
- s/randomize_addr/randomize_page/ (Kees Cook)
- PAGE_ALIGN(start) if it wasn't (Kees Cook, Michael Ellerman)
drivers/char/random.c | 33 +++++++++++++++++++++++++++++++++
include/linux/random.h | 1 +
2 files changed, 34 insertions(+)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0158d3bff7e5..61cb434e3bea 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1840,6 +1840,39 @@ randomize_range(unsigned long start, unsigned long end, unsigned long len)
return PAGE_ALIGN(get_random_int() % range + start);
}
+/**
+ * randomize_page - Generate a random, page aligned address
+ * @start: The smallest acceptable address the caller will take.
+ * @range: The size of the area, starting at @start, within which the
+ * random address must fall.
+ *
+ * If @start + @range would overflow, @range is capped.
+ *
+ * NOTE: Historical use of randomize_range, which this replaces, presumed that
+ * @start was already page aligned. We now align it regardless.
+ *
+ * Return: A page aligned address within [start, start + range). On error,
+ * @start is returned.
+ */
+unsigned long
+randomize_page(unsigned long start, unsigned long range)
+{
+ if (!PAGE_ALIGNED(start)) {
+ range -= PAGE_ALIGN(start) - start;
+ start = PAGE_ALIGN(start);
+ }
+
+ if (start > ULONG_MAX - range)
+ range = ULONG_MAX - start;
+
+ range >>= PAGE_SHIFT;
+
+ if (range == 0)
+ return start;
+
+ return start + (get_random_long() % range << PAGE_SHIFT);
+}
+
/* Interface for in-kernel drivers of true hardware RNGs.
* Those devices may produce endless random bits and will be throttled
* when our pool is full.
diff --git a/include/linux/random.h b/include/linux/random.h
index e47e533742b5..098fec690d65 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -35,6 +35,7 @@ extern const struct file_operations random_fops, urandom_fops;
unsigned int get_random_int(void);
unsigned long get_random_long(void);
unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);
+unsigned long randomize_page(unsigned long start, unsigned long range);
u32 prandom_u32(void);
void prandom_bytes(void *buf, size_t nbytes);
--
2.9.2
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