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, 81 insertions, 0 deletions

diff --git a/security/landlock/setup.c b/security/landlock/setup.c
new file mode 100644
index 000000000..47dac1736
--- /dev/null
+++ b/security/landlock/setup.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Security framework setup
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/bits.h>
+#include <linux/init.h>
+#include <linux/lsm_hooks.h>
+#include <uapi/linux/lsm.h>
+
+#include "common.h"
+#include "cred.h"
+#include "errata.h"
+#include "fs.h"
+#include "id.h"
+#include "net.h"
+#include "setup.h"
+#include "task.h"
+
+bool landlock_initialized __ro_after_init = false;
+
+const struct lsm_id landlock_lsmid = {
+	.name = LANDLOCK_NAME,
+	.id = LSM_ID_LANDLOCK,
+};
+
+struct lsm_blob_sizes landlock_blob_sizes __ro_after_init = {
+	.lbs_cred = sizeof(struct landlock_cred_security),
+	.lbs_file = sizeof(struct landlock_file_security),
+	.lbs_inode = sizeof(struct landlock_inode_security),
+	.lbs_superblock = sizeof(struct landlock_superblock_security),
+};
+
+int landlock_errata __ro_after_init;
+
+static void __init compute_errata(void)
+{
+	size_t i;
+
+#ifndef __has_include
+	/*
+	 * This is a safeguard to make sure the compiler implements
+	 * __has_include (see errata.h).
+	 */
+	WARN_ON_ONCE(1);
+	return;
+#endif
+
+	for (i = 0; landlock_errata_init[i].number; i++) {
+		const int prev_errata = landlock_errata;
+
+		if (WARN_ON_ONCE(landlock_errata_init[i].abi >
+				 landlock_abi_version))
+			continue;
+
+		landlock_errata |= BIT(landlock_errata_init[i].number - 1);
+		WARN_ON_ONCE(prev_errata == landlock_errata);
+	}
+}
+
+static int __init landlock_init(void)
+{
+	compute_errata();
+	landlock_add_cred_hooks();
+	landlock_add_task_hooks();
+	landlock_add_fs_hooks();
+	landlock_add_net_hooks();
+	landlock_init_id();
+	landlock_initialized = true;
+	pr_info("Up and running.\n");
+	return 0;
+}
+
+DEFINE_LSM(LANDLOCK_NAME) = {
+	.id = &landlock_lsmid,
+	.init = landlock_init,
+	.blobs = &landlock_blob_sizes,
+};