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, 38 insertions, 0 deletions

diff --git a/arch/arc/boot/Makefile b/arch/arc/boot/Makefile
new file mode 100644
index 000000000..5a8550124
--- /dev/null
+++ b/arch/arc/boot/Makefile
@@ -0,0 +1,38 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# uImage build relies on mkimage being available on your host for ARC target
+# You will need to build u-boot for ARC, rename mkimage to arc-elf32-mkimage
+# and make sure it's reachable from your PATH
+
+OBJCOPYFLAGS= -O binary -R .note -R .note.gnu.build-id -R .comment -S
+
+LINUX_START_TEXT = $$($(READELF) -h vmlinux | \
+			grep "Entry point address" | grep -o 0x.*)
+
+UIMAGE_LOADADDR    = $(CONFIG_LINUX_LINK_BASE)
+UIMAGE_ENTRYADDR   = $(LINUX_START_TEXT)
+
+targets += vmlinux.bin
+targets += vmlinux.bin.gz
+targets += vmlinux.bin.lzma
+targets += uImage.bin
+targets += uImage.gz
+targets += uImage.lzma
+
+$(obj)/vmlinux.bin: vmlinux FORCE
+	$(call if_changed,objcopy)
+
+$(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,gzip)
+
+$(obj)/vmlinux.bin.lzma: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,lzma)
+
+$(obj)/uImage.bin: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,uimage,none)
+
+$(obj)/uImage.gz: $(obj)/vmlinux.bin.gz FORCE
+	$(call if_changed,uimage,gzip)
+
+$(obj)/uImage.lzma: $(obj)/vmlinux.bin.lzma FORCE
+	$(call if_changed,uimage,lzma)