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, 27 insertions, 0 deletions

diff --git a/fs/minix/Kconfig b/fs/minix/Kconfig
new file mode 100644
index 000000000..90ddfad2a
--- /dev/null
+++ b/fs/minix/Kconfig
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config MINIX_FS
+	tristate "Minix file system support"
+	depends on BLOCK
+	select BUFFER_HEAD
+	help
+	  Minix is a simple operating system used in many classes about OS's.
+	  The minix file system (method to organize files on a hard disk
+	  partition or a floppy disk) was the original file system for Linux,
+	  but has been superseded by the second extended file system ext2fs.
+	  You don't want to use the minix file system on your hard disk
+	  because of certain built-in restrictions, but it is sometimes found
+	  on older Linux floppy disks.  This option will enlarge your kernel
+	  by about 28 KB. If unsure, say N.
+
+	  To compile this file system support as a module, choose M here: the
+	  module will be called minix.  Note that the file system of your root
+	  partition (the one containing the directory /) cannot be compiled as
+	  a module.
+
+config MINIX_FS_NATIVE_ENDIAN
+	def_bool MINIX_FS
+	depends on MICROBLAZE || MIPS || S390 || SUPERH || SPARC || XTENSA || (M68K && !MMU)
+
+config MINIX_FS_BIG_ENDIAN_16BIT_INDEXED
+	def_bool MINIX_FS
+	depends on M68K && MMU