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, 41 insertions, 0 deletions

diff --git a/arch/mips/Makefile.postlink b/arch/mips/Makefile.postlink
new file mode 100644
index 000000000..ea0add7d5
--- /dev/null
+++ b/arch/mips/Makefile.postlink
@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: GPL-2.0
+# ===========================================================================
+# Post-link MIPS pass
+# ===========================================================================
+#
+# 1. Check that Loongson3 LL/SC workarounds are applied correctly
+# 2. Insert relocations into vmlinux
+
+PHONY := __archpost
+__archpost:
+
+-include include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+
+CMD_LS3_LLSC = arch/mips/tools/loongson3-llsc-check
+quiet_cmd_ls3_llsc = LLSCCHK $@
+      cmd_ls3_llsc = $(CMD_LS3_LLSC) $@
+
+CMD_RELOCS = arch/mips/boot/tools/relocs
+quiet_cmd_relocs = RELOCS  $@
+      cmd_relocs = $(CMD_RELOCS) $@
+
+# `@true` prevents complaint when there is nothing to be done
+
+vmlinux vmlinux.unstripped: FORCE
+	@true
+ifeq ($(CONFIG_CPU_LOONGSON3_WORKAROUNDS),y)
+	$(call if_changed,ls3_llsc)
+endif
+ifeq ($(CONFIG_RELOCATABLE),y)
+	$(call if_changed,relocs)
+endif
+
+clean:
+	@true
+
+PHONY += FORCE clean
+
+FORCE:
+
+.PHONY: $(PHONY)