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, 25 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-kernel-btf b/Documentation/ABI/testing/sysfs-kernel-btf
new file mode 100644
index 000000000..fe96efdc9
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-btf
@@ -0,0 +1,25 @@
+What:		/sys/kernel/btf
+Date:		Aug 2019
+KernelVersion:	5.5
+Contact:	bpf@vger.kernel.org
+Description:
+		Contains BTF type information and related data for kernel and
+		kernel modules.
+
+What:		/sys/kernel/btf/vmlinux
+Date:		Aug 2019
+KernelVersion:	5.5
+Contact:	bpf@vger.kernel.org
+Description:
+		Read-only binary attribute exposing kernel's own BTF type
+		information with description of all internal kernel types. See
+		Documentation/bpf/btf.rst for detailed description of format
+		itself.
+
+What:		/sys/kernel/btf/<module-name>
+Date:		Nov 2020
+KernelVersion:	5.11
+Contact:	bpf@vger.kernel.org
+Description:
+		Read-only binary attribute exposing kernel module's BTF type
+		information as an add-on to the kernel's BTF (/sys/kernel/btf/vmlinux).