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/include/uapi/xen/gntalloc.h b/include/uapi/xen/gntalloc.h
new file mode 100644
index 000000000..310928267
--- /dev/null
+++ b/include/uapi/xen/gntalloc.h
@@ -0,0 +1,87 @@
+/******************************************************************************
+ * gntalloc.h
+ *
+ * Interface to /dev/xen/gntalloc.
+ *
+ * Author: Daniel De Graaf <dgdegra@tycho.nsa.gov>
+ *
+ * This file is in the public domain.
+ */
+
+#ifndef __LINUX_PUBLIC_GNTALLOC_H__
+#define __LINUX_PUBLIC_GNTALLOC_H__
+
+#include <linux/types.h>
+
+/*
+ * Allocates a new page and creates a new grant reference.
+ */
+#define IOCTL_GNTALLOC_ALLOC_GREF \
+_IOC(_IOC_NONE, 'G', 5, sizeof(struct ioctl_gntalloc_alloc_gref))
+struct ioctl_gntalloc_alloc_gref {
+	/* IN parameters */
+	/* The ID of the domain to be given access to the grants. */
+	__u16 domid;
+	/* Flags for this mapping */
+	__u16 flags;
+	/* Number of pages to map */
+	__u32 count;
+	/* OUT parameters */
+	/* The offset to be used on a subsequent call to mmap(). */
+	__u64 index;
+	/* The grant references of the newly created grant, one per page */
+	/* Variable size, depending on count */
+	union {
+		__u32 gref_ids[1];
+		__DECLARE_FLEX_ARRAY(__u32, gref_ids_flex);
+	};
+};
+
+#define GNTALLOC_FLAG_WRITABLE 1
+
+/*
+ * Deallocates the grant reference, allowing the associated page to be freed if
+ * no other domains are using it.
+ */
+#define IOCTL_GNTALLOC_DEALLOC_GREF \
+_IOC(_IOC_NONE, 'G', 6, sizeof(struct ioctl_gntalloc_dealloc_gref))
+struct ioctl_gntalloc_dealloc_gref {
+	/* IN parameters */
+	/* The offset returned in the map operation */
+	__u64 index;
+	/* Number of references to unmap */
+	__u32 count;
+};
+
+/*
+ * Sets up an unmap notification within the page, so that the other side can do
+ * cleanup if this side crashes. Required to implement cross-domain robust
+ * mutexes or close notification on communication channels.
+ *
+ * Each mapped page only supports one notification; multiple calls referring to
+ * the same page overwrite the previous notification. You must clear the
+ * notification prior to the IOCTL_GNTALLOC_DEALLOC_GREF if you do not want it
+ * to occur.
+ */
+#define IOCTL_GNTALLOC_SET_UNMAP_NOTIFY \
+_IOC(_IOC_NONE, 'G', 7, sizeof(struct ioctl_gntalloc_unmap_notify))
+struct ioctl_gntalloc_unmap_notify {
+	/* IN parameters */
+	/* Offset in the file descriptor for a byte within the page (same as
+	 * used in mmap). If using UNMAP_NOTIFY_CLEAR_BYTE, this is the byte to
+	 * be cleared. Otherwise, it can be any byte in the page whose
+	 * notification we are adjusting.
+	 */
+	__u64 index;
+	/* Action(s) to take on unmap */
+	__u32 action;
+	/* Event channel to notify */
+	__u32 event_channel_port;
+};
+
+/* Clear (set to zero) the byte specified by index */
+#define UNMAP_NOTIFY_CLEAR_BYTE 0x1
+/* Send an interrupt on the indicated event channel */
+#define UNMAP_NOTIFY_SEND_EVENT 0x2
+
+#endif /* __LINUX_PUBLIC_GNTALLOC_H__ */