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, 30 insertions, 0 deletions

diff --git a/scripts/Makefile.defconf b/scripts/Makefile.defconf
new file mode 100644
index 000000000..a44307f08
--- /dev/null
+++ b/scripts/Makefile.defconf
@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: GPL-2.0
+# Configuration heplers
+
+cmd_merge_fragments = \
+	$(srctree)/scripts/kconfig/merge_config.sh \
+	$4 -m -O $(objtree) $(srctree)/arch/$(SRCARCH)/configs/$2 \
+	$(foreach config,$3,$(srctree)/arch/$(SRCARCH)/configs/$(config).config)
+
+# Creates 'merged defconfigs'
+# ---------------------------------------------------------------------------
+# Usage:
+#   $(call merge_into_defconfig,base_config,config_fragment1 config_fragment2 ...)
+#
+# Input config fragments without '.config' suffix
+define merge_into_defconfig
+	$(call cmd,merge_fragments,$1,$2)
+	+$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
+endef
+
+
+# Creates 'merged defconfigs without warning about overrides'
+# ---------------------------------------------------------------------------
+# Usage:
+#   $(call merge_into_defconfig_override,base_config,config_fragment1 config_fragment2 ...)
+#
+# Input config fragments without '.config' suffix
+define merge_into_defconfig_override
+	$(call cmd,merge_fragments,$1,$2,-Q)
+	+$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
+endef