pstore/pmsg: drop bounce buffer

Removing a bounce buffer copy operation in the pmsg driver path is
always better. We also gain in overall performance by not requesting
a vmalloc on every write as this can cause precious RT tasks, such
as user facing media operation, to stall while memory is being
reclaimed. Added a write_buf_user to the pstore functions, a backup
platform write_buf_user that uses the small buffer that is part of
the instance, and implemented a ramoops write_buf_user that only
supports PSTORE_TYPE_PMSG.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 6 insertions, 29 deletions

diff --git a/fs/pstore/pmsg.c b/fs/pstore/pmsg.c
index 7de20cd3797f..78f6176c020f 100644
--- a/fs/pstore/pmsg.c
+++ b/fs/pstore/pmsg.c
@@ -19,48 +19,25 @@
 #include "internal.h"
 
 static DEFINE_MUTEX(pmsg_lock);
-#define PMSG_MAX_BOUNCE_BUFFER_SIZE (2*PAGE_SIZE)
 
 static ssize_t write_pmsg(struct file *file, const char __user *buf,
 			  size_t count, loff_t *ppos)
 {
-	size_t i, buffer_size;
-	char *buffer;
+	u64 id;
+	int ret;
 
 	if (!count)
 		return 0;
 
+	/* check outside lock, page in any data. write_buf_user also checks */
 	if (!access_ok(VERIFY_READ, buf, count))
 		return -EFAULT;
 
-	buffer_size = count;
-	if (buffer_size > PMSG_MAX_BOUNCE_BUFFER_SIZE)
-		buffer_size = PMSG_MAX_BOUNCE_BUFFER_SIZE;
-	buffer = vmalloc(buffer_size);
-	if (!buffer)
-		return -ENOMEM;
-
 	mutex_lock(&pmsg_lock);
-	for (i = 0; i < count; ) {
-		size_t c = min(count - i, buffer_size);
-		u64 id;
-		long ret;
-
-		ret = __copy_from_user(buffer, buf + i, c);
-		if (unlikely(ret != 0)) {
-			mutex_unlock(&pmsg_lock);
-			vfree(buffer);
-			return -EFAULT;
-		}
-		psinfo->write_buf(PSTORE_TYPE_PMSG, 0, &id, 0, buffer, 0, c,
-				  psinfo);
-
-		i += c;
-	}
-
+	ret = psinfo->write_buf_user(PSTORE_TYPE_PMSG, 0, &id, 0, buf, 0, count,
+				     psinfo);
 	mutex_unlock(&pmsg_lock);
-	vfree(buffer);
-	return count;
+	return ret ? ret : count;
 }
 
 static const struct file_operations pmsg_fops = {