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, 52 insertions, 0 deletions

diff --git a/tools/perf/util/tracepoint.c b/tools/perf/util/tracepoint.c
new file mode 100644
index 000000000..95377ed5d
--- /dev/null
+++ b/tools/perf/util/tracepoint.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "tracepoint.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/param.h>
+#include <unistd.h>
+
+#include <api/fs/tracing_path.h>
+#include "fncache.h"
+
+int tp_event_has_id(const char *dir_path, struct dirent *evt_dir)
+{
+	char evt_path[MAXPATHLEN];
+	int fd;
+
+	snprintf(evt_path, MAXPATHLEN, "%s/%s/id", dir_path, evt_dir->d_name);
+	fd = open(evt_path, O_RDONLY);
+	if (fd < 0)
+		return -EINVAL;
+	close(fd);
+
+	return 0;
+}
+
+/*
+ * Check whether event is in <debugfs_mount_point>/tracing/events
+ */
+bool is_valid_tracepoint(const char *event_string)
+{
+	char *dst, *path = malloc(strlen(event_string) + 4); /* Space for "/id\0". */
+	bool have_file = false; /* Conservatively return false if memory allocation failed. */
+	const char *src;
+
+	if (!path)
+		return false;
+
+	/* Copy event_string replacing the ':' with '/'. */
+	for (src = event_string, dst = path; *src; src++, dst++)
+		*dst = (*src == ':') ? '/' : *src;
+	/* Add "/id\0". */
+	memcpy(dst, "/id", 4);
+
+	dst = get_events_file(path);
+	if (dst)
+		have_file = file_available(dst);
+	free(dst);
+	free(path);
+	return have_file;
+}