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, 87 insertions, 0 deletions

diff --git a/rust/helpers/atomic_ext.c b/rust/helpers/atomic_ext.c
new file mode 100644
index 000000000..c267d5190
--- /dev/null
+++ b/rust/helpers/atomic_ext.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <asm/barrier.h>
+#include <asm/rwonce.h>
+#include <linux/atomic.h>
+
+#define GEN_READ_HELPER(tname, type)						\
+__rust_helper type rust_helper_atomic_##tname##_read(type *ptr)			\
+{										\
+	return READ_ONCE(*ptr);							\
+}
+
+#define GEN_SET_HELPER(tname, type)						\
+__rust_helper void rust_helper_atomic_##tname##_set(type *ptr, type val)	\
+{										\
+	WRITE_ONCE(*ptr, val);							\
+}
+
+#define GEN_READ_ACQUIRE_HELPER(tname, type)					\
+__rust_helper type rust_helper_atomic_##tname##_read_acquire(type *ptr)		\
+{										\
+	return smp_load_acquire(ptr);						\
+}
+
+#define GEN_SET_RELEASE_HELPER(tname, type)					\
+__rust_helper void rust_helper_atomic_##tname##_set_release(type *ptr, type val)\
+{										\
+	smp_store_release(ptr, val);						\
+}
+
+#define GEN_READ_SET_HELPERS(tname, type)					\
+	GEN_READ_HELPER(tname, type)						\
+	GEN_SET_HELPER(tname, type)						\
+	GEN_READ_ACQUIRE_HELPER(tname, type)					\
+	GEN_SET_RELEASE_HELPER(tname, type)					\
+
+GEN_READ_SET_HELPERS(i8, s8)
+GEN_READ_SET_HELPERS(i16, s16)
+GEN_READ_SET_HELPERS(ptr, const void *)
+
+/*
+ * xchg helpers depend on ARCH_SUPPORTS_ATOMIC_RMW and on the
+ * architecture provding xchg() support for i8 and i16.
+ *
+ * The architectures that currently support Rust (x86_64, armv7,
+ * arm64, riscv, and loongarch) satisfy these requirements.
+ */
+#define GEN_XCHG_HELPER(tname, type, suffix)					\
+__rust_helper type								\
+rust_helper_atomic_##tname##_xchg##suffix(type *ptr, type new)			\
+{										\
+	return xchg##suffix(ptr, new);					\
+}
+
+#define GEN_XCHG_HELPERS(tname, type)						\
+	GEN_XCHG_HELPER(tname, type, )						\
+	GEN_XCHG_HELPER(tname, type, _acquire)					\
+	GEN_XCHG_HELPER(tname, type, _release)					\
+	GEN_XCHG_HELPER(tname, type, _relaxed)					\
+
+GEN_XCHG_HELPERS(i8, s8)
+GEN_XCHG_HELPERS(i16, s16)
+GEN_XCHG_HELPERS(ptr, const void *)
+
+/*
+ * try_cmpxchg helpers depend on ARCH_SUPPORTS_ATOMIC_RMW and on the
+ * architecture provding try_cmpxchg() support for i8 and i16.
+ *
+ * The architectures that currently support Rust (x86_64, armv7,
+ * arm64, riscv, and loongarch) satisfy these requirements.
+ */
+#define GEN_TRY_CMPXCHG_HELPER(tname, type, suffix)				\
+__rust_helper bool								\
+rust_helper_atomic_##tname##_try_cmpxchg##suffix(type *ptr, type *old, type new)\
+{										\
+	return try_cmpxchg##suffix(ptr, old, new);				\
+}
+
+#define GEN_TRY_CMPXCHG_HELPERS(tname, type)					\
+	GEN_TRY_CMPXCHG_HELPER(tname, type, )					\
+	GEN_TRY_CMPXCHG_HELPER(tname, type, _acquire)				\
+	GEN_TRY_CMPXCHG_HELPER(tname, type, _release)				\
+	GEN_TRY_CMPXCHG_HELPER(tname, type, _relaxed)				\
+
+GEN_TRY_CMPXCHG_HELPERS(i8, s8)
+GEN_TRY_CMPXCHG_HELPERS(i16, s16)
+GEN_TRY_CMPXCHG_HELPERS(ptr, const void *)