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, 18 insertions, 0 deletions

diff --git a/arch/mips/lib/Makefile b/arch/mips/lib/Makefile
new file mode 100644
index 000000000..5d5b993cb
--- /dev/null
+++ b/arch/mips/lib/Makefile
@@ -0,0 +1,18 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for MIPS-specific library files..
+#
+
+lib-y	+= bitops.o csum_partial.o delay.o memcpy.o memset.o \
+	   mips-atomic.o strncpy_user.o \
+	   strnlen_user.o uncached.o
+
+obj-y			+= iomap_copy.o
+obj-$(CONFIG_PCI)	+= iomap-pci.o
+lib-$(CONFIG_GENERIC_CSUM)	:= $(filter-out csum_partial.o, $(lib-y))
+
+obj-$(CONFIG_CPU_GENERIC_DUMP_TLB) += dump_tlb.o
+obj-$(CONFIG_CPU_R3000)		+= r3k_dump_tlb.o
+
+# libgcc-style stuff needed in the kernel
+obj-y += bswapsi.o bswapdi.o multi3.o