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, 71 insertions, 0 deletions

diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
new file mode 100644
index 000000000..a68b1bea5
--- /dev/null
+++ b/Documentation/userspace-api/index.rst
@@ -0,0 +1,71 @@
+=====================================
+The Linux kernel user-space API guide
+=====================================
+
+.. _man-pages: https://www.kernel.org/doc/man-pages/
+
+While much of the kernel's user-space API is documented elsewhere
+(particularly in the man-pages_ project), some user-space information can
+also be found in the kernel tree itself.  This manual is intended to be the
+place where this information is gathered.
+
+
+System calls
+============
+
+.. toctree::
+   :maxdepth: 1
+
+   unshare
+   futex2
+   ebpf/index
+   ioctl/index
+   mseal
+   rseq
+
+Security-related interfaces
+===========================
+
+.. toctree::
+   :maxdepth: 1
+
+   no_new_privs
+   seccomp_filter
+   landlock
+   lsm
+   mfd_noexec
+   spec_ctrl
+   tee
+   check_exec
+
+Devices and I/O
+===============
+
+.. toctree::
+   :maxdepth: 1
+
+   accelerators/ocxl
+   dma-buf-heaps
+   dma-buf-alloc-exchange
+   fwctl/index
+   gpio/index
+   iommufd
+   media/index
+   dcdbas
+   vduse
+   isapnp
+
+Everything else
+===============
+
+.. toctree::
+   :maxdepth: 1
+
+   ELF
+   liveupdate
+   netlink/index
+   sysfs-platform_profile
+   vduse
+   futex2
+   perf_ring_buffer
+   ntsync