openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/fs/affs/Kconfig b/fs/affs/Kconfig
new file mode 100644
index 000000000..1ae432d26
--- /dev/null
+++ b/fs/affs/Kconfig
@@ -0,0 +1,24 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config AFFS_FS
+	tristate "Amiga FFS file system support"
+	depends on BLOCK
+	select BUFFER_HEAD
+	select LEGACY_DIRECT_IO
+	help
+	  The Fast File System (FFS) is the common file system used on hard
+	  disks by Amiga(tm) systems since AmigaOS Version 1.3 (34.20).  Say Y
+	  if you want to be able to read and write files from and to an Amiga
+	  FFS partition on your hard drive.  Amiga floppies however cannot be
+	  read with this driver due to an incompatibility of the floppy
+	  controller used in an Amiga and the standard floppy controller in
+	  PCs and workstations. Read <file:Documentation/filesystems/affs.rst>
+	  and <file:fs/affs/Changes>.
+
+	  With this driver you can also mount disk files used by Bernd
+	  Schmidt's Un*X Amiga Emulator
+	  (<http://www.freiburg.linux.de/~uae/>).
+	  If you want to do this, you will also need to say Y or M to "Loop
+	  device support", above.
+
+	  To compile this file system support as a module, choose M here: the
+	  module will be called affs.  If unsure, say N.