AZL-100697

In the Linux kernel, the following vulnerability has been resolved:

openrisc: fix arbitrary kernel memory access via or1k_atomic syscall

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]