Merge branch 'handle-possible-null-trusted-raw_tp-arguments'

Kumar Kartikeya Dwivedi says:

====================
Handle possible NULL trusted raw_tp arguments

More context is available in [0], but the TLDR; is that the verifier
incorrectly assumes that any raw tracepoint argument will always be
non-NULL. This means that even when users correctly check possible NULL
arguments, the verifier can remove the NULL check due to incorrect
knowledge of the NULL-ness of the pointer. Secondly, kernel helpers or
kfuncs taking these trusted tracepoint arguments incorrectly assume that
all arguments will always be valid non-NULL.

In this set, we mark raw_tp arguments as PTR_MAYBE_NULL on top of
PTR_TRUSTED, but special case their behavior when dereferencing them or
pointer arithmetic over them is involved. When passing trusted args to
helpers or kfuncs, raw_tp programs are permitted to pass possibly NULL
pointers in such cases.

Any loads into such maybe NULL trusted PTR_TO_BTF_ID is promoted to a
PROBE_MEM load to handle emanating page faults. The verifier will ensure
NULL checks on such pointers are preserved and do not lead to dead code
elimination.

This new behavior is not applied when ref_obj_id is non-zero, as those
pointers do not belong to raw_tp arguments, but instead acquired
objects.

Since helpers and kfuncs already require attention for PTR_TO_BTF_ID
(non-trusted) pointers, we do not implement any protection for such
cases in this patch set, and leave it as future work for an upcoming
series.

A selftest is included with this patch set to verify the new behavior,
and it crashes the kernel without the first patch.

 [0]: https://lore.kernel.org/bpf/CAADnVQLMPPavJQR6JFsi3dtaaLHB816JN4HCV_TFWohJ61D+wQ@mail.gmail.com

Changelog:
----------
v2 -> v3
v2: https://lore.kernel.org/bpf/20241103184144.3765700-1-memxor@gmail.com

 * Fix lenient check around check_ptr_to_btf_access allowing any
   PTR_TO_BTF_ID with PTR_MAYBE_NULL to be deref'd.
 * Add Juri and Jiri's Tested-by, Reviewed-by resp.

v1 -> v2
v1: https://lore.kernel.org/bpf/20241101000017.3424165-1-memxor@gmail.com

 * Add patch to clean up users of gettid (Andrii)
 * Avoid nested blocks in sefltest (Andrii)
 * Prevent code motion optimization in selftest using barrier()
====================

Link: https://lore.kernel.org/r/20241104171959.2938862-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

10 files changed, 45 insertions, 20 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
index 070c52c312e5..6befa870434b 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
@@ -690,7 +690,7 @@ void test_bpf_cookie(void)
 	if (!ASSERT_OK_PTR(skel, "skel_open"))
 		return;
 
-	skel->bss->my_tid = syscall(SYS_gettid);
+	skel->bss->my_tid = sys_gettid();
 
 	if (test__start_subtest("kprobe"))
 		kprobe_subtest(skel);
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index 9006549a1294..b8e1224cfd19 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -226,7 +226,7 @@ static void test_task_common_nocheck(struct bpf_iter_attach_opts *opts,
 	ASSERT_OK(pthread_create(&thread_id, NULL, &do_nothing_wait, NULL),
 		  "pthread_create");
 
-	skel->bss->tid = syscall(SYS_gettid);
+	skel->bss->tid = sys_gettid();
 
 	do_dummy_read_opts(skel->progs.dump_task, opts);
 
@@ -255,10 +255,10 @@ static void *run_test_task_tid(void *arg)
 	union bpf_iter_link_info linfo;
 	int num_unknown_tid, num_known_tid;
 
-	ASSERT_NEQ(getpid(), syscall(SYS_gettid), "check_new_thread_id");
+	ASSERT_NEQ(getpid(), sys_gettid(), "check_new_thread_id");
 
 	memset(&linfo, 0, sizeof(linfo));
-	linfo.task.tid = syscall(SYS_gettid);
+	linfo.task.tid = sys_gettid();
 	opts.link_info = &linfo;
 	opts.link_info_len = sizeof(linfo);
 	test_task_common(&opts, 0, 1);
diff --git a/tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c b/tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c
index 747761572098..9015e2c2ab12 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c
@@ -63,14 +63,14 @@ static void test_tp_btf(int cgroup_fd)
 	if (!ASSERT_OK(err, "map_delete_elem"))
 		goto out;
 
-	skel->bss->target_pid = syscall(SYS_gettid);
+	skel->bss->target_pid = sys_gettid();
 
 	err = cgrp_ls_tp_btf__attach(skel);
 	if (!ASSERT_OK(err, "skel_attach"))
 		goto out;
 
-	syscall(SYS_gettid);
-	syscall(SYS_gettid);
+	sys_gettid();
+	sys_gettid();
 
 	skel->bss->target_pid = 0;
 
@@ -154,7 +154,7 @@ static void test_recursion(int cgroup_fd)
 		goto out;
 
 	/* trigger sys_enter, make sure it does not cause deadlock */
-	syscall(SYS_gettid);
+	sys_gettid();
 
 out:
 	cgrp_ls_recursion__destroy(skel);
@@ -224,7 +224,7 @@ static void test_yes_rcu_lock(__u64 cgroup_id)
 		return;
 
 	CGROUP_MODE_SET(skel);
-	skel->bss->target_pid = syscall(SYS_gettid);
+	skel->bss->target_pid = sys_gettid();
 
 	bpf_program__set_autoload(skel->progs.yes_rcu_lock, true);
 	err = cgrp_ls_sleepable__load(skel);
diff --git a/tools/testing/selftests/bpf/prog_tests/core_reloc.c b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
index 26019313e1fc..1c682550e0e7 100644
--- a/tools/testing/selftests/bpf/prog_tests/core_reloc.c
+++ b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
@@ -1010,7 +1010,7 @@ static void run_core_reloc_tests(bool use_btfgen)
 	struct data *data;
 	void *mmap_data = NULL;
 
-	my_pid_tgid = getpid() | ((uint64_t)syscall(SYS_gettid) << 32);
+	my_pid_tgid = getpid() | ((uint64_t)sys_gettid() << 32);
 
 	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
 		char btf_file[] = "/tmp/core_reloc.btf.XXXXXX";
diff --git a/tools/testing/selftests/bpf/prog_tests/linked_funcs.c b/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
index cad664546912..fa639b021f7e 100644
--- a/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
+++ b/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
@@ -20,7 +20,7 @@ void test_linked_funcs(void)
 	bpf_program__set_autoload(skel->progs.handler1, true);
 	bpf_program__set_autoload(skel->progs.handler2, true);
 
-	skel->rodata->my_tid = syscall(SYS_gettid);
+	skel->rodata->my_tid = sys_gettid();
 	skel->bss->syscall_id = SYS_getpgid;
 
 	err = linked_funcs__load(skel);
diff --git a/tools/testing/selftests/bpf/prog_tests/ns_current_pid_tgid.c b/tools/testing/selftests/bpf/prog_tests/ns_current_pid_tgid.c
index c29787e092d6..761ce24bce38 100644
--- a/tools/testing/selftests/bpf/prog_tests/ns_current_pid_tgid.c
+++ b/tools/testing/selftests/bpf/prog_tests/ns_current_pid_tgid.c
@@ -23,7 +23,7 @@ static int get_pid_tgid(pid_t *pid, pid_t *tgid,
 	struct stat st;
 	int err;
 
-	*pid = syscall(SYS_gettid);
+	*pid = sys_gettid();
 	*tgid = getpid();
 
 	err = stat("/proc/self/ns/pid", &st);
diff --git a/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c b/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c
new file mode 100644
index 000000000000..6fa19449297e
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include "raw_tp_null.skel.h"
+
+void test_raw_tp_null(void)
+{
+	struct raw_tp_null *skel;
+
+	skel = raw_tp_null__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "raw_tp_null__open_and_load"))
+		return;
+
+	skel->bss->tid = sys_gettid();
+
+	if (!ASSERT_OK(raw_tp_null__attach(skel), "raw_tp_null__attach"))
+		goto end;
+
+	ASSERT_OK(trigger_module_test_read(2), "trigger testmod read");
+	ASSERT_EQ(skel->bss->i, 3, "invocations");
+
+end:
+	raw_tp_null__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c b/tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c
index a1f7e7378a64..ebe0c12b5536 100644
--- a/tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c
+++ b/tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c
@@ -21,7 +21,7 @@ static void test_success(void)
 	if (!ASSERT_OK_PTR(skel, "skel_open"))
 		return;
 
-	skel->bss->target_pid = syscall(SYS_gettid);
+	skel->bss->target_pid = sys_gettid();
 
 	bpf_program__set_autoload(skel->progs.get_cgroup_id, true);
 	bpf_program__set_autoload(skel->progs.task_succ, true);
@@ -58,7 +58,7 @@ static void test_rcuptr_acquire(void)
 	if (!ASSERT_OK_PTR(skel, "skel_open"))
 		return;
 
-	skel->bss->target_pid = syscall(SYS_gettid);
+	skel->bss->target_pid = sys_gettid();
 
 	bpf_program__set_autoload(skel->progs.task_acquire, true);
 	err = rcu_read_lock__load(skel);
diff --git a/tools/testing/selftests/bpf/prog_tests/task_local_storage.c b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
index 00cc9d0aee5d..60f474d965a9 100644
--- a/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
+++ b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c
@@ -31,14 +31,14 @@ static void test_sys_enter_exit(void)
 	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
 		return;
 
-	skel->bss->target_pid = syscall(SYS_gettid);
+	skel->bss->target_pid = sys_gettid();
 
 	err = task_local_storage__attach(skel);
 	if (!ASSERT_OK(err, "skel_attach"))
 		goto out;
 
-	syscall(SYS_gettid);
-	syscall(SYS_gettid);
+	sys_gettid();
+	sys_gettid();
 
 	/* 3x syscalls: 1x attach and 2x gettid */
 	ASSERT_EQ(skel->bss->enter_cnt, 3, "enter_cnt");
@@ -107,7 +107,7 @@ static void test_recursion(void)
 
 	/* trigger sys_enter, make sure it does not cause deadlock */
 	skel->bss->test_pid = getpid();
-	syscall(SYS_gettid);
+	sys_gettid();
 	skel->bss->test_pid = 0;
 	task_ls_recursion__detach(skel);
 
@@ -262,7 +262,7 @@ static void test_uptr_basic(void)
 	__u64 ev_dummy_data = 1;
 	int err;
 
-	my_tid = syscall(SYS_gettid);
+	my_tid = sys_gettid();
 	parent_task_fd = sys_pidfd_open(my_tid, 0);
 	if (!ASSERT_OK_FD(parent_task_fd, "parent_task_fd"))
 		return;
diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
index 2c39902b8a09..619b31cd24a1 100644
--- a/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
@@ -125,7 +125,7 @@ static void *child_thread(void *ctx)
 	struct child *child = ctx;
 	int c = 0, err;
 
-	child->tid = syscall(SYS_gettid);
+	child->tid = sys_gettid();
 
 	/* let parent know we are ready */
 	err = write(child->c2p[1], &c, 1);