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, 46 insertions, 0 deletions

diff --git a/arch/alpha/lib/Makefile b/arch/alpha/lib/Makefile
new file mode 100644
index 000000000..84046e730
--- /dev/null
+++ b/arch/alpha/lib/Makefile
@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for alpha-specific library files..
+#
+
+asflags-y := $(KBUILD_CFLAGS)
+
+# Many of these routines have implementations tuned for ev6.
+# Choose them iff we're targeting ev6 specifically.
+ev6-$(CONFIG_ALPHA_EV6) := ev6-
+
+# Several make use of the cttz instruction introduced in ev67.
+ev67-$(CONFIG_ALPHA_EV67) := ev67-
+
+lib-y =	__divqu.o __remqu.o __divlu.o __remlu.o \
+	udiv-qrnnd.o \
+	udelay.o \
+	$(ev6-y)memset.o \
+	$(ev6-y)memcpy.o \
+	memmove.o \
+	checksum.o \
+	csum_partial_copy.o \
+	$(ev67-y)strlen.o \
+	stycpy.o \
+	styncpy.o \
+	$(ev67-y)strchr.o \
+	$(ev67-y)strrchr.o \
+	$(ev6-y)memchr.o \
+	$(ev6-y)copy_user.o \
+	$(ev6-y)clear_user.o \
+	$(ev6-y)csum_ipv6_magic.o \
+	$(ev6-y)clear_page.o \
+	$(ev6-y)copy_page.o \
+	fpreg.o \
+	callback_srm.o srm_puts.o srm_printk.o \
+	fls.o
+
+# The division routines are built from single source, with different defines.
+AFLAGS___divqu.o = -DDIV
+AFLAGS___remqu.o =       -DREM
+AFLAGS___divlu.o = -DDIV       -DINTSIZE
+AFLAGS___remlu.o =       -DREM -DINTSIZE
+
+$(addprefix $(obj)/,__divqu.o __remqu.o __divlu.o __remlu.o): \
+						$(src)/$(ev6-y)divide.S FORCE
+	$(call if_changed_rule,as_o_S)