2014-06-22 07:30:18

by James A Shackleford

Subject: [PATCH] staging: goldfish: fix direct copy_to_user() from __iomem

This patch allocates a few pages and performs an ioread8_rep() from the bus
address, which are then copied to userspace. This fixes the sparse warning:

drivers/staging/goldfish/goldfish_audio.c:136:43: warning: incorrect type in argument 2 (different address spaces)
drivers/staging/goldfish/goldfish_audio.c:136:43: expected void const *from
drivers/staging/goldfish/goldfish_audio.c:136:43: got char [noderef] <asn:2>*read_buffer

which was a result of performing a copy_to_user() directly from the bus address
to the userspace, which can be unsafe across some architectures.

Signed-off-by: James A Shackleford <[email protected]>
---
drivers/staging/goldfish/goldfish_audio.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/goldfish/goldfish_audio.c b/drivers/staging/goldfish/goldfish_audio.c
index a166424..535ed20 100644
--- a/drivers/staging/goldfish/goldfish_audio.c
+++ b/drivers/staging/goldfish/goldfish_audio.c
@@ -118,10 +118,17 @@ static ssize_t goldfish_audio_read(struct file *fp, char __user *buf,
struct goldfish_audio *data = fp->private_data;
int length;
int result = 0;
+ unsigned int order;
+ void *read_buffer;

if (!data->read_supported)
return -ENODEV;

+ order = get_order(READ_BUFFER_SIZE);
+ read_buffer = (void *)__get_free_pages(GFP_KERNEL, order);
+ if (!read_buffer)
+ return -ENOMEM;
+
while (count > 0) {
length = (count > READ_BUFFER_SIZE ? READ_BUFFER_SIZE : count);
AUDIO_WRITE(data, AUDIO_START_READ, length);
@@ -129,17 +136,21 @@ static ssize_t goldfish_audio_read(struct file *fp, char __user *buf,
wait_event_interruptible(data->wait,
(data->buffer_status & AUDIO_INT_READ_BUFFER_FULL));

- length = AUDIO_READ(data,
- AUDIO_READ_BUFFER_AVAILABLE);
+ length = AUDIO_READ(data, AUDIO_READ_BUFFER_AVAILABLE);

/* copy data to user space */
- if (copy_to_user(buf, data->read_buffer, length))
- return -EFAULT;
+ ioread8_rep(data->read_buffer, read_buffer, length);
+ if (copy_to_user(buf, read_buffer, length)) {
+ result = -EFAULT;
+ goto error;
+ }

result += length;
buf += length;
count -= length;
}
+error:
+ __free_pages(read_buffer, order);
return result;
}

--
1.7.9.5

2014-06-23 10:59:00

by Alan

Subject: Re: [PATCH] staging: goldfish: fix direct copy_to_user() from __iomem

On Sun, 2014-06-22 at 03:29 -0400, James A Shackleford wrote:
> This patch allocates a few pages and performs an ioread8_rep() from the bus
> address, which are then copied to userspace. This fixes the sparse warning:
>
> drivers/staging/goldfish/goldfish_audio.c:136:43: warning: incorrect type in argument 2 (different address spaces)
> drivers/staging/goldfish/goldfish_audio.c:136:43: expected void const *from
> drivers/staging/goldfish/goldfish_audio.c:136:43: got char [noderef] <asn:2>*read_buffer
>
> which was a result of performing a copy_to_user() directly from the bus address
> to the userspace, which can be unsafe across some architectures.

Goldfish is a specific architecture. It shouldn't be doing direct
xcopies like that - which is why the code is in staging but at the same
time allocating a buffer each call and doing extra copies is not the
right answer.

It should be mapping the pages when they are first set up.

Alan