From 6fcd486b3a0a628c41f12b3a7329a18a2c74b351 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Thu, 2 Mar 2023 20:14:46 -0800 Subject: bpf: Refactor RCU enforcement in the verifier. bpf_rcu_read_lock/unlock() are only available in clang compiled kernels. Lack of such key mechanism makes it impossible for sleepable bpf programs to use RCU pointers. Allow bpf_rcu_read_lock/unlock() in GCC compiled kernels (though GCC doesn't support btf_type_tag yet) and allowlist certain field dereferences in important data structures like tast_struct, cgroup, socket that are used by sleepable programs either as RCU pointer or full trusted pointer (which is valid outside of RCU CS). Use BTF_TYPE_SAFE_RCU and BTF_TYPE_SAFE_TRUSTED macros for such tagging. They will be removed once GCC supports btf_type_tag. With that refactor check_ptr_to_btf_access(). Make it strict in enforcing PTR_TRUSTED and PTR_UNTRUSTED while deprecating old PTR_TO_BTF_ID without modifier flags. There is a chance that this strict enforcement might break existing programs (especially on GCC compiled kernels), but this cleanup has to start sooner than later. Note PTR_TO_CTX access still yields old deprecated PTR_TO_BTF_ID. Once it's converted to strict PTR_TRUSTED or PTR_UNTRUSTED the kfuncs and helpers will be able to default to KF_TRUSTED_ARGS. KF_RCU will remain as a weaker version of KF_TRUSTED_ARGS where obj refcnt could be 0. Adjust rcu_read_lock selftest to run on gcc and clang compiled kernels. Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Acked-by: David Vernet Link: https://lore.kernel.org/bpf/20230303041446.3630-7-alexei.starovoitov@gmail.com --- .../selftests/bpf/prog_tests/cgrp_local_storage.c | 14 +++++++------- tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c | 16 +++------------- tools/testing/selftests/bpf/progs/cgrp_ls_sleepable.c | 4 ++-- tools/testing/selftests/bpf/progs/cpumask_failure.c | 2 +- tools/testing/selftests/bpf/progs/nested_trust_failure.c | 2 +- tools/testing/selftests/bpf/progs/rcu_read_lock.c | 6 +++--- tools/testing/selftests/bpf/verifier/calls.c | 2 +- 7 files changed, 18 insertions(+), 28 deletions(-) (limited to 'tools') 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 2cc759956e3b..63e776f4176e 100644 --- a/tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c +++ b/tools/testing/selftests/bpf/prog_tests/cgrp_local_storage.c @@ -193,7 +193,7 @@ out: cgrp_ls_sleepable__destroy(skel); } -static void test_no_rcu_lock(__u64 cgroup_id) +static void test_yes_rcu_lock(__u64 cgroup_id) { struct cgrp_ls_sleepable *skel; int err; @@ -204,7 +204,7 @@ static void test_no_rcu_lock(__u64 cgroup_id) skel->bss->target_pid = syscall(SYS_gettid); - bpf_program__set_autoload(skel->progs.no_rcu_lock, true); + bpf_program__set_autoload(skel->progs.yes_rcu_lock, true); err = cgrp_ls_sleepable__load(skel); if (!ASSERT_OK(err, "skel_load")) goto out; @@ -220,7 +220,7 @@ out: cgrp_ls_sleepable__destroy(skel); } -static void test_rcu_lock(void) +static void test_no_rcu_lock(void) { struct cgrp_ls_sleepable *skel; int err; @@ -229,7 +229,7 @@ static void test_rcu_lock(void) if (!ASSERT_OK_PTR(skel, "skel_open")) return; - bpf_program__set_autoload(skel->progs.yes_rcu_lock, true); + bpf_program__set_autoload(skel->progs.no_rcu_lock, true); err = cgrp_ls_sleepable__load(skel); ASSERT_ERR(err, "skel_load"); @@ -256,10 +256,10 @@ void test_cgrp_local_storage(void) test_negative(); if (test__start_subtest("cgroup_iter_sleepable")) test_cgroup_iter_sleepable(cgroup_fd, cgroup_id); + if (test__start_subtest("yes_rcu_lock")) + test_yes_rcu_lock(cgroup_id); if (test__start_subtest("no_rcu_lock")) - test_no_rcu_lock(cgroup_id); - if (test__start_subtest("rcu_lock")) - test_rcu_lock(); + test_no_rcu_lock(); close(cgroup_fd); } 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 447d8560ecb6..3f1f58d3a729 100644 --- a/tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c +++ b/tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c @@ -25,10 +25,10 @@ static void test_success(void) bpf_program__set_autoload(skel->progs.get_cgroup_id, true); bpf_program__set_autoload(skel->progs.task_succ, true); - bpf_program__set_autoload(skel->progs.no_lock, true); bpf_program__set_autoload(skel->progs.two_regions, true); bpf_program__set_autoload(skel->progs.non_sleepable_1, true); bpf_program__set_autoload(skel->progs.non_sleepable_2, true); + bpf_program__set_autoload(skel->progs.task_trusted_non_rcuptr, true); err = rcu_read_lock__load(skel); if (!ASSERT_OK(err, "skel_load")) goto out; @@ -69,6 +69,7 @@ out: static const char * const inproper_region_tests[] = { "miss_lock", + "no_lock", "miss_unlock", "non_sleepable_rcu_mismatch", "inproper_sleepable_helper", @@ -99,7 +100,6 @@ out: } static const char * const rcuptr_misuse_tests[] = { - "task_untrusted_non_rcuptr", "task_untrusted_rcuptr", "cross_rcu_region", }; @@ -128,17 +128,8 @@ out: void test_rcu_read_lock(void) { - struct btf *vmlinux_btf; int cgroup_fd; - vmlinux_btf = btf__load_vmlinux_btf(); - if (!ASSERT_OK_PTR(vmlinux_btf, "could not load vmlinux BTF")) - return; - if (btf__find_by_name_kind(vmlinux_btf, "rcu", BTF_KIND_TYPE_TAG) < 0) { - test__skip(); - goto out; - } - cgroup_fd = test__join_cgroup("/rcu_read_lock"); if (!ASSERT_GE(cgroup_fd, 0, "join_cgroup /rcu_read_lock")) goto out; @@ -153,6 +144,5 @@ void test_rcu_read_lock(void) if (test__start_subtest("negative_tests_rcuptr_misuse")) test_rcuptr_misuse(); close(cgroup_fd); -out: - btf__free(vmlinux_btf); +out:; } diff --git a/tools/testing/selftests/bpf/progs/cgrp_ls_sleepable.c b/tools/testing/selftests/bpf/progs/cgrp_ls_sleepable.c index 2d11ed528b6f..7615dc23d301 100644 --- a/tools/testing/selftests/bpf/progs/cgrp_ls_sleepable.c +++ b/tools/testing/selftests/bpf/progs/cgrp_ls_sleepable.c @@ -49,7 +49,7 @@ int no_rcu_lock(void *ctx) if (task->pid != target_pid) return 0; - /* ptr_to_btf_id semantics. should work. */ + /* task->cgroups is untrusted in sleepable prog outside of RCU CS */ cgrp = task->cgroups->dfl_cgrp; ptr = bpf_cgrp_storage_get(&map_a, cgrp, 0, BPF_LOCAL_STORAGE_GET_F_CREATE); @@ -71,7 +71,7 @@ int yes_rcu_lock(void *ctx) bpf_rcu_read_lock(); cgrp = task->cgroups->dfl_cgrp; - /* cgrp is untrusted and cannot pass to bpf_cgrp_storage_get() helper. */ + /* cgrp is trusted under RCU CS */ ptr = bpf_cgrp_storage_get(&map_a, cgrp, 0, BPF_LOCAL_STORAGE_GET_F_CREATE); if (ptr) cgroup_id = cgrp->kn->id; diff --git a/tools/testing/selftests/bpf/progs/cpumask_failure.c b/tools/testing/selftests/bpf/progs/cpumask_failure.c index 33e8e86dd090..c16f7563b84e 100644 --- a/tools/testing/selftests/bpf/progs/cpumask_failure.c +++ b/tools/testing/selftests/bpf/progs/cpumask_failure.c @@ -44,7 +44,7 @@ int BPF_PROG(test_alloc_double_release, struct task_struct *task, u64 clone_flag } SEC("tp_btf/task_newtask") -__failure __msg("bpf_cpumask_acquire args#0 expected pointer to STRUCT bpf_cpumask") +__failure __msg("must be referenced") int BPF_PROG(test_acquire_wrong_cpumask, struct task_struct *task, u64 clone_flags) { struct bpf_cpumask *cpumask; diff --git a/tools/testing/selftests/bpf/progs/nested_trust_failure.c b/tools/testing/selftests/bpf/progs/nested_trust_failure.c index 14aff7676436..0d1aa6bbace4 100644 --- a/tools/testing/selftests/bpf/progs/nested_trust_failure.c +++ b/tools/testing/selftests/bpf/progs/nested_trust_failure.c @@ -17,7 +17,7 @@ char _license[] SEC("license") = "GPL"; */ SEC("tp_btf/task_newtask") -__failure __msg("R2 must be referenced or trusted") +__failure __msg("R2 must be") int BPF_PROG(test_invalid_nested_user_cpus, struct task_struct *task, u64 clone_flags) { bpf_cpumask_test_cpu(0, task->user_cpus_ptr); diff --git a/tools/testing/selftests/bpf/progs/rcu_read_lock.c b/tools/testing/selftests/bpf/progs/rcu_read_lock.c index 5cecbdbbb16e..7250bb76d18a 100644 --- a/tools/testing/selftests/bpf/progs/rcu_read_lock.c +++ b/tools/testing/selftests/bpf/progs/rcu_read_lock.c @@ -81,7 +81,7 @@ int no_lock(void *ctx) { struct task_struct *task, *real_parent; - /* no bpf_rcu_read_lock(), old code still works */ + /* old style ptr_to_btf_id is not allowed in sleepable */ task = bpf_get_current_task_btf(); real_parent = task->real_parent; (void)bpf_task_storage_get(&map_a, real_parent, 0, 0); @@ -286,13 +286,13 @@ out: } SEC("?fentry.s/" SYS_PREFIX "sys_getpgid") -int task_untrusted_non_rcuptr(void *ctx) +int task_trusted_non_rcuptr(void *ctx) { struct task_struct *task, *group_leader; task = bpf_get_current_task_btf(); bpf_rcu_read_lock(); - /* the pointer group_leader marked as untrusted */ + /* the pointer group_leader is explicitly marked as trusted */ group_leader = task->real_parent->group_leader; (void)bpf_task_storage_get(&map_a, group_leader, 0, 0); bpf_rcu_read_unlock(); diff --git a/tools/testing/selftests/bpf/verifier/calls.c b/tools/testing/selftests/bpf/verifier/calls.c index 9a326a800e5c..5702fc9761ef 100644 --- a/tools/testing/selftests/bpf/verifier/calls.c +++ b/tools/testing/selftests/bpf/verifier/calls.c @@ -181,7 +181,7 @@ }, .result_unpriv = REJECT, .result = REJECT, - .errstr = "negative offset ptr_ ptr R1 off=-4 disallowed", + .errstr = "ptr R1 off=-4 disallowed", }, { "calls: invalid kfunc call: PTR_TO_BTF_ID with variable offset", -- cgit v1.2.3