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, 21 insertions, 0 deletions

diff --git a/block/error-injection.h b/block/error-injection.h
new file mode 100644
index 000000000..9821d773a
--- /dev/null
+++ b/block/error-injection.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BLK_ERROR_INJECTION_H
+#define _BLK_ERROR_INJECTION_H 1
+
+#include <linux/jump_label.h>
+
+DECLARE_STATIC_KEY_FALSE(blk_error_injection_enabled);
+
+void blk_error_injection_init(struct gendisk *disk);
+void blk_error_injection_exit(struct gendisk *disk);
+bool __blk_error_inject(struct bio *bio);
+static inline bool blk_error_inject(struct bio *bio)
+{
+	if (IS_ENABLED(CONFIG_BLK_ERROR_INJECTION) &&
+	    static_branch_unlikely(&blk_error_injection_enabled) &&
+	    test_bit(GD_ERROR_INJECT, &bio->bi_bdev->bd_disk->state))
+		return __blk_error_inject(bio);
+	return false;
+}
+
+#endif /* _BLK_ERROR_INJECTION_H */