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, 23 insertions, 0 deletions

diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
new file mode 100644
index 000000000..f668b9897
--- /dev/null
+++ b/arch/riscv/lib/Makefile
@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: GPL-2.0-only
+lib-y			+= delay.o
+lib-y			+= memcpy.o
+lib-y			+= memset.o
+lib-y			+= memmove.o
+ifeq ($(CONFIG_KASAN_GENERIC)$(CONFIG_KASAN_SW_TAGS),)
+lib-y			+= strcmp.o
+lib-y			+= strlen.o
+lib-y			+= strncmp.o
+lib-y			+= strnlen.o
+lib-y			+= strchr.o
+lib-y			+= strrchr.o
+endif
+lib-y			+= csum.o
+ifeq ($(CONFIG_MMU), y)
+lib-$(CONFIG_RISCV_ISA_V)	+= uaccess_vector.o
+endif
+lib-$(CONFIG_MMU)	+= uaccess.o
+lib-$(CONFIG_32BIT)	+= ashldi3.o ashrdi3.o lshrdi3.o
+lib-$(CONFIG_64BIT)	+= tishift.o
+lib-$(CONFIG_RISCV_ISA_ZICBOZ)	+= clear_page.o
+obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
+lib-$(CONFIG_RISCV_ISA_V)	+= riscv_v_helpers.o