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, 84 insertions, 0 deletions

diff --git a/tools/perf/tests/openat-syscall.c b/tools/perf/tests/openat-syscall.c
new file mode 100644
index 000000000..b54cbe5f1
--- /dev/null
+++ b/tools/perf/tests/openat-syscall.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <errno.h>
+#include <inttypes.h>
+#include <api/fs/tracing_path.h>
+#include <linux/err.h>
+#include <linux/string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include "thread_map.h"
+#include "evsel.h"
+#include "debug.h"
+#include "tests.h"
+#include "util/counts.h"
+
+static int test__openat_syscall_event(struct test_suite *test __maybe_unused,
+				      int subtest __maybe_unused)
+{
+	int err = TEST_FAIL, fd;
+	struct evsel *evsel;
+	unsigned int nr_openat_calls = 111, i;
+	struct perf_thread_map *threads = thread_map__new_by_tid(getpid());
+	char sbuf[STRERR_BUFSIZE];
+	char errbuf[BUFSIZ];
+
+	if (threads == NULL) {
+		pr_debug("thread_map__new\n");
+		return TEST_FAIL;
+	}
+
+	evsel = evsel__newtp("syscalls", "sys_enter_openat");
+	if (IS_ERR(evsel)) {
+		tracing_path__strerror_open_tp(errno, errbuf, sizeof(errbuf), "syscalls", "sys_enter_openat");
+		pr_debug("%s\n", errbuf);
+		err = TEST_SKIP;
+		goto out_thread_map_delete;
+	}
+
+	if (evsel__open_per_thread(evsel, threads) < 0) {
+		pr_debug("failed to open counter: %s, "
+			 "tweak /proc/sys/kernel/perf_event_paranoid?\n",
+			 str_error_r(errno, sbuf, sizeof(sbuf)));
+		err = TEST_SKIP;
+		goto out_evsel_delete;
+	}
+
+	for (i = 0; i < nr_openat_calls; ++i) {
+		fd = openat(0, "/etc/passwd", O_RDONLY);
+		close(fd);
+	}
+
+	if (evsel__read_on_cpu(evsel, 0, 0) < 0) {
+		pr_debug("evsel__read_on_cpu\n");
+		goto out_close_fd;
+	}
+
+	if (perf_counts(evsel->counts, 0, 0)->val != nr_openat_calls) {
+		pr_debug("evsel__read_on_cpu: expected to intercept %d calls, got %" PRIu64 "\n",
+			 nr_openat_calls, perf_counts(evsel->counts, 0, 0)->val);
+		goto out_close_fd;
+	}
+
+	err = TEST_OK;
+out_close_fd:
+	perf_evsel__close_fd(&evsel->core);
+out_evsel_delete:
+	evsel__delete(evsel);
+out_thread_map_delete:
+	perf_thread_map__put(threads);
+	return err;
+}
+
+static struct test_case tests__openat_syscall_event[] = {
+	TEST_CASE_REASON("Detect openat syscall event",
+			 openat_syscall_event,
+			 "permissions"),
+	{	.name = NULL, }
+};
+
+struct test_suite suite__openat_syscall_event = {
+	.desc = "Detect openat syscall event",
+	.test_cases = tests__openat_syscall_event,
+};