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, 27 insertions, 0 deletions

diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
new file mode 100644
index 000000000..c729bc936
--- /dev/null
+++ b/scripts/mod/Makefile
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS_REMOVE_empty.o += $(CC_FLAGS_LTO)
+
+hostprogs-always-y	+= modpost mk_elfconfig
+always-y		+= empty.o
+
+modpost-objs	:= modpost.o file2alias.o sumversion.o symsearch.o
+
+devicetable-offsets-file := devicetable-offsets.h
+
+$(obj)/$(devicetable-offsets-file): $(obj)/devicetable-offsets.s FORCE
+	$(call filechk,offsets,__DEVICETABLE_OFFSETS_H__)
+
+targets += $(devicetable-offsets-file) devicetable-offsets.s
+
+# dependencies on generated files need to be listed explicitly
+
+$(obj)/modpost.o $(obj)/file2alias.o $(obj)/sumversion.o $(obj)/symsearch.o: $(obj)/elfconfig.h
+$(obj)/file2alias.o: $(obj)/$(devicetable-offsets-file)
+
+quiet_cmd_elfconfig = MKELF   $@
+      cmd_elfconfig = $(obj)/mk_elfconfig < $< > $@
+
+$(obj)/elfconfig.h: $(obj)/empty.o $(obj)/mk_elfconfig FORCE
+	$(call if_changed,elfconfig)
+
+targets += elfconfig.h