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, 42 insertions, 0 deletions

diff --git a/fs/adfs/dir_fplus.h b/fs/adfs/dir_fplus.h
new file mode 100644
index 000000000..d729b1591
--- /dev/null
+++ b/fs/adfs/dir_fplus.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/fs/adfs/dir_fplus.h
+ *
+ *  Copyright (C) 1999 Russell King
+ *
+ *  Structures of directories on the F+ format disk
+ */
+
+#define ADFS_FPLUS_NAME_LEN	255
+
+#define BIGDIRSTARTNAME ('S' | 'B' << 8 | 'P' << 16 | 'r' << 24)
+#define BIGDIRENDNAME	('o' | 'v' << 8 | 'e' << 16 | 'n' << 24)
+
+struct adfs_bigdirheader {
+	__u8	startmasseq;
+	__u8	bigdirversion[3];
+	__le32	bigdirstartname;
+	__le32	bigdirnamelen;
+	__le32	bigdirsize;
+	__le32	bigdirentries;
+	__le32	bigdirnamesize;
+	__le32	bigdirparent;
+	char	bigdirname[1];
+} __attribute__((packed, aligned(4)));
+
+struct adfs_bigdirentry {
+	__le32	bigdirload;
+	__le32	bigdirexec;
+	__le32	bigdirlen;
+	__le32	bigdirindaddr;
+	__le32	bigdirattr;
+	__le32	bigdirobnamelen;
+	__le32	bigdirobnameptr;
+} __attribute__((packed, aligned(4)));
+
+struct adfs_bigdirtail {
+	__le32	bigdirendname;
+	__u8	bigdirendmasseq;
+	__u8	reserved[2];
+	__u8	bigdircheckbyte;
+} __attribute__((packed, aligned(4)));