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, 92 insertions, 0 deletions

diff --git a/block/partitions/sysv68.c b/block/partitions/sysv68.c
new file mode 100644
index 000000000..470e0f9de
--- /dev/null
+++ b/block/partitions/sysv68.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  fs/partitions/sysv68.c
+ *
+ *  Copyright (C) 2007 Philippe De Muyter <phdm@macqel.be>
+ */
+
+#include "check.h"
+
+/*
+ *	Volume ID structure: on first 256-bytes sector of disk
+ */
+
+struct volumeid {
+	u8	vid_unused[248];
+	u8	vid_mac[8];	/* ASCII string "MOTOROLA" */
+};
+
+/*
+ *	config block: second 256-bytes sector on disk
+ */
+
+struct dkconfig {
+	u8	ios_unused0[128];
+	__be32	ios_slcblk;	/* Slice table block number */
+	__be16	ios_slccnt;	/* Number of entries in slice table */
+	u8	ios_unused1[122];
+};
+
+/*
+ *	combined volumeid and dkconfig block
+ */
+
+struct dkblk0 {
+	struct volumeid dk_vid;
+	struct dkconfig dk_ios;
+};
+
+/*
+ *	Slice Table Structure
+ */
+
+struct slice {
+	__be32	nblocks;		/* slice size (in blocks) */
+	__be32	blkoff;			/* block offset of slice */
+};
+
+
+int sysv68_partition(struct parsed_partitions *state)
+{
+	int i, slices;
+	int slot = 1;
+	Sector sect;
+	unsigned char *data;
+	struct dkblk0 *b;
+	struct slice *slice;
+
+	data = read_part_sector(state, 0, &sect);
+	if (!data)
+		return -1;
+
+	b = (struct dkblk0 *)data;
+	if (memcmp(b->dk_vid.vid_mac, "MOTOROLA", sizeof(b->dk_vid.vid_mac))) {
+		put_dev_sector(sect);
+		return 0;
+	}
+	slices = be16_to_cpu(b->dk_ios.ios_slccnt);
+	i = be32_to_cpu(b->dk_ios.ios_slcblk);
+	put_dev_sector(sect);
+
+	data = read_part_sector(state, i, &sect);
+	if (!data)
+		return -1;
+
+	slices -= 1; /* last slice is the whole disk */
+	seq_buf_printf(&state->pp_buf, "sysV68: %s(s%u)", state->name, slices);
+	slice = (struct slice *)data;
+	for (i = 0; i < slices; i++, slice++) {
+		if (slot == state->limit)
+			break;
+		if (be32_to_cpu(slice->nblocks)) {
+			put_partition(state, slot,
+				be32_to_cpu(slice->blkoff),
+				be32_to_cpu(slice->nblocks));
+			seq_buf_printf(&state->pp_buf, "(s%u)", i);
+		}
+		slot++;
+	}
+	seq_buf_puts(&state->pp_buf, "\n");
+	put_dev_sector(sect);
+	return 1;
+}