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, 19 insertions, 0 deletions

diff --git a/arch/mips/math-emu/Makefile b/arch/mips/math-emu/Makefile
new file mode 100644
index 000000000..81d25ff32
--- /dev/null
+++ b/arch/mips/math-emu/Makefile
@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for the Linux/MIPS kernel FPU emulation.
+#
+
+obj-y	+= cp1emu.o ieee754dp.o ieee754sp.o ieee754.o \
+	   dp_div.o dp_mul.o dp_sub.o dp_add.o dp_fsp.o dp_cmp.o dp_simple.o \
+	   dp_tint.o dp_fint.o dp_rint.o dp_maddf.o dp_2008class.o dp_fmin.o \
+	   dp_fmax.o							     \
+	   sp_div.o sp_mul.o sp_sub.o sp_add.o sp_fdp.o sp_cmp.o sp_simple.o \
+	   sp_tint.o sp_fint.o sp_rint.o sp_maddf.o sp_2008class.o sp_fmin.o \
+	   sp_fmax.o							     \
+	   dsemul.o
+
+lib-y	+= ieee754d.o \
+	   dp_tlong.o dp_flong.o dp_sqrt.o \
+	   sp_tlong.o sp_flong.o sp_sqrt.o
+
+obj-$(CONFIG_DEBUG_FS) += me-debugfs.o