Patchwork [59/88] hw_random: make buffer usable in scatterlist.

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Submitter Luis Henriques
Date March 14, 2013, 10:35 a.m.
Message ID <1363257381-15900-60-git-send-email-luis.henriques@canonical.com>
Download mbox | patch
Permalink /patch/227572/
State New
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Luis Henriques - March 14, 2013, 10:35 a.m.
3.5.7.8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rusty Russell <rusty@rustcorp.com.au>

commit f7f154f1246ccc5a0a7e9ce50932627d60a0c878 upstream.

virtio_rng feeds the randomness buffer handed by the core directly
into the scatterlist, since commit bb347d98079a547e80bd4722dee1de61e4dca0e8.

However, if CONFIG_HW_RANDOM=m, the static buffer isn't a linear address
(at least on most archs).  We could fix this in virtio_rng, but it's actually
far easier to just do it in the core as virtio_rng would have to allocate
a buffer every time (it doesn't know how much the core will want to read).

Reported-by: Aurelien Jarno <aurelien@aurel32.net>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 drivers/char/hw_random/core.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

Patch

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 1bafb40..69ae597 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -40,6 +40,7 @@ 
 #include <linux/init.h>
 #include <linux/miscdevice.h>
 #include <linux/delay.h>
+#include <linux/slab.h>
 #include <asm/uaccess.h>
 
 
@@ -52,8 +53,12 @@  static struct hwrng *current_rng;
 static LIST_HEAD(rng_list);
 static DEFINE_MUTEX(rng_mutex);
 static int data_avail;
-static u8 rng_buffer[SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES]
-	__cacheline_aligned;
+static u8 *rng_buffer;
+
+static size_t rng_buffer_size(void)
+{
+	return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
+}
 
 static inline int hwrng_init(struct hwrng *rng)
 {
@@ -116,7 +121,7 @@  static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 
 		if (!data_avail) {
 			bytes_read = rng_get_data(current_rng, rng_buffer,
-				sizeof(rng_buffer),
+				rng_buffer_size(),
 				!(filp->f_flags & O_NONBLOCK));
 			if (bytes_read < 0) {
 				err = bytes_read;
@@ -307,6 +312,14 @@  int hwrng_register(struct hwrng *rng)
 
 	mutex_lock(&rng_mutex);
 
+	/* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
+	err = -ENOMEM;
+	if (!rng_buffer) {
+		rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
+		if (!rng_buffer)
+			goto out_unlock;
+	}
+
 	/* Must not register two RNGs with the same name. */
 	err = -EEXIST;
 	list_for_each_entry(tmp, &rng_list, list) {