Now that BPF supports adding new kernel functions with kfuncs, and storing
kernel objects in maps with kptrs, we can add a set of kfuncs which allow
struct task_struct objects to be stored in maps as referenced kptrs.
The possible use cases for doing this are plentiful. During tracing,
for example, it would be useful to be able to collect some tasks that
performed a certain operation, and then periodically summarize who they
are, which cgroup they're in, how much CPU time they've utilized, etc.
Doing this now would require storing the task's pids along with some
relevant data to be exported to user space, and later associating the
pids to tasks in other event handlers where the data is recorded.
Another useful by-product of this is that it allows a program to pin a
task in a BPF program, and by proxy therefore also e.g. pin its task
local storage.
In order to support this, we'll need to expand KF_TRUSTED_ARGS to
support receiving trusted, non-refcounted pointers. It currently only
supports either PTR_TO_CTX pointers, or refcounted pointers . What this
means in terms of implementation is that btf_check_func_arg_match()
would have to add another condition to its logic for checking if
a ptr needs a refcount to also require that the pointer has at least one
type modifier, such as PTR_UNTRUSTED. PTR_UNTRUSTED does not cover all
of the possible pointers we need to watch out for, though. For example,
a pointer obtained from walking a struct is considered "trusted" (or at
least, not PTR_UNTRUSTED). To account for this and enable us to expand
KF_TRUSTED_ARGS, this patch set also introduces a new PTR_NESTED type
flag modifier which records if a pointer was obtained from walking a
struct.
This patch set adds this new PTR_NESTED type flag, expands
KF_TRUSTED_ARGS accordingly, adds the new set of kfuncs mentioned above,
and then finally adds a new selftest suite to validate all of this new
behavior.
David Vernet (3):
bpf: Allow trusted pointers to be passed to KF_TRUSTED_ARGS kfuncs
bpf: Add kfuncs for storing struct task_struct * as a kptr
bpf/selftests: Add selftests for new task kfuncs
include/linux/bpf.h | 6 +
kernel/bpf/btf.c | 11 +-
kernel/bpf/helpers.c | 86 ++++-
kernel/bpf/verifier.c | 15 +-
tools/testing/selftests/bpf/DENYLIST.s390x | 1 +
.../selftests/bpf/prog_tests/task_kfunc.c | 160 +++++++++
.../selftests/bpf/progs/task_kfunc_common.h | 83 +++++
.../selftests/bpf/progs/task_kfunc_failure.c | 315 ++++++++++++++++++
.../selftests/bpf/progs/task_kfunc_success.c | 132 ++++++++
tools/testing/selftests/bpf/verifier/calls.c | 4 +-
10 files changed, 804 insertions(+), 9 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/task_kfunc.c
create mode 100644 tools/testing/selftests/bpf/progs/task_kfunc_common.h
create mode 100644 tools/testing/selftests/bpf/progs/task_kfunc_failure.c
create mode 100644 tools/testing/selftests/bpf/progs/task_kfunc_success.c
--
2.38.0
Now that BPF supports adding new kernel functions with kfuncs, and
storing kernel objects in maps with kptrs, we can add a set of kfuncs
which allow struct task_struct objects to be stored in maps as
referenced kptrs. The possible use cases for doing this are plentiful.
During tracing, for example, it would be useful to be able to collect
some tasks that performed a certain operation, and then periodically
summarize who they are, which cgroup they're in, how much CPU time
they've utilized, etc.
In order to enable this, this patch adds three new kfuncs:
struct task_struct *bpf_task_acquire(struct task_struct *p);
struct task_struct *bpf_task_kptr_get(struct task_struct **pp);
void bpf_task_release(struct task_struct *p);
A follow-on patch will add selftests validating these kfuncs.
Signed-off-by: David Vernet <[email protected]>
---
kernel/bpf/helpers.c | 86 +++++++++++++++++++++++++++++++++++++++++---
1 file changed, 81 insertions(+), 5 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index a6b04faed282..9d0307969977 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1700,20 +1700,96 @@ bpf_base_func_proto(enum bpf_func_id func_id)
}
}
-BTF_SET8_START(tracing_btf_ids)
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+ "Global functions as their definitions will be in vmlinux BTF");
+
+/**
+ * bpf_task_acquire - Acquire a reference to a task. A task acquired by this
+ * kfunc which is not stored in a map as a kptr, must be released by calling
+ * bpf_task_release().
+ * @p: The task on which a reference is being acquired.
+ */
+__used noinline
+struct task_struct *bpf_task_acquire(struct task_struct *p)
+{
+ if (!p)
+ return NULL;
+
+ refcount_inc(&p->rcu_users);
+ return p;
+}
+
+/**
+ * bpf_task_kptr_get - Acquire a reference on a struct task_struct kptr. A task
+ * kptr acquired by this kfunc which is not subsequently stored in a map, must
+ * be released by calling bpf_task_release().
+ * @pp: A pointer to a task kptr on which a reference is being acquired.
+ */
+__used noinline
+struct task_struct *bpf_task_kptr_get(struct task_struct **pp)
+{
+ struct task_struct *p;
+
+ rcu_read_lock();
+ p = READ_ONCE(*pp);
+ if (p && !refcount_inc_not_zero(&p->rcu_users))
+ p = NULL;
+ rcu_read_unlock();
+
+ return p;
+}
+
+/**
+ * bpf_task_release - Release the reference acquired on a struct task_struct *.
+ * If this kfunc is invoked in an RCU read region, the task_struct is
+ * guaranteed to not be freed until the current grace period has ended, even if
+ * its refcount drops to 0.
+ * @p: The task on which a reference is being released.
+ */
+__used noinline void bpf_task_release(struct task_struct *p)
+{
+ if (!p)
+ return;
+
+ put_task_struct_rcu_user(p);
+}
+
+__diag_pop();
+
+BTF_SET8_START(generic_kfunc_btf_ids)
#ifdef CONFIG_KEXEC_CORE
BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)
#endif
-BTF_SET8_END(tracing_btf_ids)
+BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_RET_NULL | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_task_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE | KF_TRUSTED_ARGS)
+BTF_SET8_END(generic_kfunc_btf_ids)
-static const struct btf_kfunc_id_set tracing_kfunc_set = {
+static const struct btf_kfunc_id_set generic_kfunc_set = {
.owner = THIS_MODULE,
- .set = &tracing_btf_ids,
+ .set = &generic_kfunc_btf_ids,
};
+BTF_ID_LIST(generic_kfunc_dtor_ids)
+BTF_ID(struct, task_struct)
+BTF_ID(func, bpf_task_release)
+
static int __init kfunc_init(void)
{
- return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &tracing_kfunc_set);
+ int ret;
+ const struct btf_id_dtor_kfunc generic_kfunc_dtors[] = {
+ {
+ .btf_id = generic_kfunc_dtor_ids[0],
+ .kfunc_btf_id = generic_kfunc_dtor_ids[1]
+ },
+ };
+
+ ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &generic_kfunc_set);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &generic_kfunc_set);
+ return ret ?: register_btf_id_dtor_kfuncs(generic_kfunc_dtors,
+ ARRAY_SIZE(generic_kfunc_dtors),
+ THIS_MODULE);
}
late_initcall(kfunc_init);
--
2.38.0
Kfuncs currently support specifying the KF_TRUSTED_ARGS flag to signal
to the verifier that it should enforce that a BPF program passes it a
"safe", trusted pointer. Currently, "safe" means that the pointer is
either PTR_TO_CTX, or is refcounted. There may be cases, however, where
the kernel passes a BPF program a safe / trusted pointer to an object
that the BPF program wishes to use as a kptr, but because the object
does not yet have a ref_obj_id from the perspective of the verifier, the
program would be unable to pass it to a KF_ACQUIRE | KF_TRUSTED_ARGS
kfunc.
The solution is to expand the set of pointers that are considered
trusted according to KF_TRUSTED_ARGS, so that programs can invoke kfuncs
with these pointers without getting rejected by the verifier.
There is already a PTR_UNTRUSTED flag that is set in some scenarios,
such as when a BPF program reads a kptr directly from a map
without performing a bpf_kptr_xchg() call. These pointers of course can
and should be rejected by the verifier. Unfortunately, however,
PTR_UNTRUSTED does not cover all the cases for safety that need to
be addressed to adequately protect kfuncs. Specifically, pointers
obtained by a BPF program "walking" a struct are _not_ considered
PTR_UNTRUSTED according to BPF. For example, say that we were to add a
kfunc called bpf_task_acquire(), with KF_ACQUIRE | KF_TRUSTED_ARGS, to
acquire a struct task_struct *. If we only used PTR_UNTRUSTED to signal
that a task was unsafe to pass to a kfunc, the verifier would mistakenly
allow the following unsafe BPF program to be loaded:
SEC("tp_btf/task_newtask")
int BPF_PROG(unsafe_acquire_task,
struct task_struct *task,
u64 clone_flags)
{
struct task_struct *acquired, *nested;
nested = task->last_wakee;
/* Would not be rejected by the verifier. */
acquired = bpf_task_acquire(nested);
if (!acquired)
return 0;
bpf_task_release(acquired);
return 0;
}
To address this, this patch defines a new type flag called PTR_NESTED
which tracks whether a PTR_TO_BTF_ID pointer was retrieved from walking
a struct. A pointer passed directly from the kernel begins with
(PTR_NESTED & type) == 0, meaning of course that it is not nested. Any
pointer received from walking that object, however, would inherit that
flag and become a nested pointer.
With that flag, this patch also updates btf_check_func_arg_match() to
only flag a PTR_TO_BTF_ID object as requiring a refcount if it has any
type modifiers (which of course includes both PTR_UNTRUSTED and
PTR_NESTED). Otherwise, the pointer passes this check and continues
onto the others in btf_check_func_arg_match().
A subsequent patch will add kfuncs for storing a task kfunc as a kptr,
and then another patch will validate this feature by ensuring that the
verifier rejects a kfunc invocation with a nested pointer.
Signed-off-by: David Vernet <[email protected]>
---
include/linux/bpf.h | 6 ++++++
kernel/bpf/btf.c | 11 ++++++++++-
kernel/bpf/verifier.c | 15 ++++++++++++++-
tools/testing/selftests/bpf/verifier/calls.c | 4 ++--
4 files changed, 32 insertions(+), 4 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 9e7d46d16032..b624024edb4e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -457,6 +457,12 @@ enum bpf_type_flag {
/* Size is known at compile time. */
MEM_FIXED_SIZE = BIT(10 + BPF_BASE_TYPE_BITS),
+ /* PTR was obtained from walking a struct. This is used with
+ * PTR_TO_BTF_ID to determine whether the pointer is safe to pass to a
+ * kfunc with KF_TRUSTED_ARGS.
+ */
+ PTR_NESTED = BIT(11 + BPF_BASE_TYPE_BITS),
+
__BPF_TYPE_FLAG_MAX,
__BPF_TYPE_LAST_FLAG = __BPF_TYPE_FLAG_MAX - 1,
};
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index eba603cec2c5..3d7bad11b10b 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6333,8 +6333,17 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
/* Check if argument must be a referenced pointer, args + i has
* been verified to be a pointer (after skipping modifiers).
* PTR_TO_CTX is ok without having non-zero ref_obj_id.
+ *
+ * All object pointers must be refcounted, other than:
+ * - PTR_TO_CTX
+ * - Trusted pointers (i.e. pointers with no type modifiers)
*/
- if (is_kfunc && trusted_args && (obj_ptr && reg->type != PTR_TO_CTX) && !reg->ref_obj_id) {
+ if (is_kfunc &&
+ trusted_args &&
+ obj_ptr &&
+ base_type(reg->type) != PTR_TO_CTX &&
+ type_flag(reg->type) &&
+ !reg->ref_obj_id) {
bpf_log(log, "R%d must be referenced\n", regno);
return -EINVAL;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6f6d2d511c06..a625aaddeb34 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -581,6 +581,8 @@ static const char *reg_type_str(struct bpf_verifier_env *env,
strncpy(prefix, "user_", 32);
if (type & MEM_PERCPU)
strncpy(prefix, "percpu_", 32);
+ if (type & PTR_NESTED)
+ strncpy(prefix, "nested_", 32);
if (type & PTR_UNTRUSTED)
strncpy(prefix, "untrusted_", 32);
@@ -4558,6 +4560,9 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
if (type_flag(reg->type) & PTR_UNTRUSTED)
flag |= PTR_UNTRUSTED;
+ /* A pointer can only be unwalked when it wasn't accessed by walking a struct. */
+ flag |= PTR_NESTED;
+
if (atype == BPF_READ && value_regno >= 0)
mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id, flag);
@@ -5694,7 +5699,12 @@ static const struct bpf_reg_types scalar_types = { .types = { SCALAR_VALUE } };
static const struct bpf_reg_types context_types = { .types = { PTR_TO_CTX } };
static const struct bpf_reg_types alloc_mem_types = { .types = { PTR_TO_MEM | MEM_ALLOC } };
static const struct bpf_reg_types const_map_ptr_types = { .types = { CONST_PTR_TO_MAP } };
-static const struct bpf_reg_types btf_ptr_types = { .types = { PTR_TO_BTF_ID } };
+static const struct bpf_reg_types btf_ptr_types = {
+ .types = {
+ PTR_TO_BTF_ID,
+ PTR_TO_BTF_ID | PTR_NESTED
+ },
+};
static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALUE } };
static const struct bpf_reg_types percpu_btf_ptr_types = { .types = { PTR_TO_BTF_ID | MEM_PERCPU } };
static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC } };
@@ -5768,6 +5778,9 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
if (arg_type & PTR_MAYBE_NULL)
type &= ~PTR_MAYBE_NULL;
+ if (!(arg_type & ARG_PTR_TO_BTF_ID))
+ type &= ~PTR_NESTED;
+
for (i = 0; i < ARRAY_SIZE(compatible->types); i++) {
expected = compatible->types[i];
if (expected == NOT_INIT)
diff --git a/tools/testing/selftests/bpf/verifier/calls.c b/tools/testing/selftests/bpf/verifier/calls.c
index e1a937277b54..496c29b1a298 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 = "negative offset nested_ptr_ ptr R1 off=-4 disallowed",
},
{
"calls: invalid kfunc call: PTR_TO_BTF_ID with variable offset",
@@ -243,7 +243,7 @@
},
.result_unpriv = REJECT,
.result = REJECT,
- .errstr = "R1 must be referenced",
+ .errstr = "arg#0 pointer type STRUCT prog_test_ref_kfunc must point to scalar",
},
{
"calls: valid kfunc call: referenced arg needs refcounted PTR_TO_BTF_ID",
--
2.38.0
A previous change added a series of kfuncs for storing struct
task_struct objects as referenced kptrs. This patch adds a new
task_kfunc test suite for validating their expected behavior.
Signed-off-by: David Vernet <[email protected]>
---
tools/testing/selftests/bpf/DENYLIST.s390x | 1 +
.../selftests/bpf/prog_tests/task_kfunc.c | 160 +++++++++
.../selftests/bpf/progs/task_kfunc_common.h | 83 +++++
.../selftests/bpf/progs/task_kfunc_failure.c | 315 ++++++++++++++++++
.../selftests/bpf/progs/task_kfunc_success.c | 132 ++++++++
5 files changed, 691 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/task_kfunc.c
create mode 100644 tools/testing/selftests/bpf/progs/task_kfunc_common.h
create mode 100644 tools/testing/selftests/bpf/progs/task_kfunc_failure.c
create mode 100644 tools/testing/selftests/bpf/progs/task_kfunc_success.c
diff --git a/tools/testing/selftests/bpf/DENYLIST.s390x b/tools/testing/selftests/bpf/DENYLIST.s390x
index 520f12229b98..323a0e312b3d 100644
--- a/tools/testing/selftests/bpf/DENYLIST.s390x
+++ b/tools/testing/selftests/bpf/DENYLIST.s390x
@@ -52,6 +52,7 @@ skc_to_unix_sock # could not attach BPF object unexpecte
socket_cookie # prog_attach unexpected error: -524 (trampoline)
stacktrace_build_id # compare_map_keys stackid_hmap vs. stackmap err -2 errno 2 (?)
tailcalls # tail_calls are not allowed in non-JITed programs with bpf-to-bpf calls (?)
+task_kfunc # JIT does not support calling kernel function
task_local_storage # failed to auto-attach program 'trace_exit_creds': -524 (trampoline)
test_bpffs # bpffs test failed 255 (iterator)
test_bprm_opts # failed to auto-attach program 'secure_exec': -524 (trampoline)
diff --git a/tools/testing/selftests/bpf/prog_tests/task_kfunc.c b/tools/testing/selftests/bpf/prog_tests/task_kfunc.c
new file mode 100644
index 000000000000..18492d010c45
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/task_kfunc.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+
+#define _GNU_SOURCE
+#include <sys/wait.h>
+#include <test_progs.h>
+#include <unistd.h>
+
+#include "task_kfunc_failure.skel.h"
+#include "task_kfunc_success.skel.h"
+
+static size_t log_buf_sz = 1 << 20; /* 1 MB */
+static char obj_log_buf[1048576];
+
+static struct task_kfunc_success *open_load_task_kfunc_skel(void)
+{
+ struct task_kfunc_success *skel;
+ int err;
+
+ skel = task_kfunc_success__open();
+ if (!ASSERT_OK_PTR(skel, "skel_open"))
+ return NULL;
+
+ skel->bss->pid = getpid();
+
+ err = task_kfunc_success__load(skel);
+ if (!ASSERT_OK(err, "skel_load"))
+ goto cleanup;
+
+ return skel;
+
+cleanup:
+ task_kfunc_success__destroy(skel);
+ return NULL;
+}
+
+static void run_success_test(const char *prog_name)
+{
+ struct task_kfunc_success *skel;
+ int status;
+ pid_t child_pid;
+ struct bpf_program *prog;
+ struct bpf_link *link = NULL;
+
+ skel = open_load_task_kfunc_skel();
+ if (!ASSERT_OK_PTR(skel, "open_load_skel"))
+ return;
+
+ if (!ASSERT_OK(skel->bss->err, "pre_spawn_err"))
+ goto cleanup;
+
+ prog = bpf_object__find_program_by_name(skel->obj, prog_name);
+ if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
+ goto cleanup;
+
+ link = bpf_program__attach(prog);
+ if (!ASSERT_OK_PTR(link, "attached_link"))
+ goto cleanup;
+
+ child_pid = fork();
+ if (!ASSERT_GT(child_pid, -1, "child_pid"))
+ goto cleanup;
+ if (child_pid == 0)
+ _exit(0);
+ waitpid(child_pid, &status, 0);
+
+ ASSERT_OK(skel->bss->err, "post_wait_err");
+
+cleanup:
+ bpf_link__destroy(link);
+ task_kfunc_success__destroy(skel);
+}
+
+static const char * const success_tests[] = {
+ "test_task_acquire_release_argument",
+ "test_task_acquire_release_current",
+ "test_task_acquire_leave_in_map",
+ "test_task_xchg_release",
+ "test_task_get_release",
+};
+
+static struct {
+ const char *prog_name;
+ const char *expected_err_msg;
+} failure_tests[] = {
+ {"task_kfunc_acquire_untrusted", "arg#0 pointer type STRUCT task_struct must point"},
+ {"task_kfunc_acquire_fp", "arg#0 pointer type STRUCT task_struct must point"},
+ {"task_kfunc_acquire_no_null_check", "arg#0 pointer type STRUCT task_struct must point"},
+ {"task_kfunc_acquire_trusted_nested", "arg#0 pointer type STRUCT task_struct must point"},
+ {"task_kfunc_acquire_null", "arg#0 pointer type STRUCT task_struct must point"},
+ {"task_kfunc_acquire_unreleased", "Unreleased reference"},
+ {"task_kfunc_get_non_kptr_param", "arg#0 expected pointer to map value"},
+ {"task_kfunc_get_non_kptr_acquired", "arg#0 expected pointer to map value"},
+ {"task_kfunc_get_null", "arg#0 expected pointer to map value"},
+ {"task_kfunc_xchg_unreleased", "Unreleased reference"},
+ {"task_kfunc_get_unreleased", "Unreleased reference"},
+ {"task_kfunc_release_untrusted", "arg#0 pointer type STRUCT task_struct must point"},
+ {"task_kfunc_release_fp", "arg#0 pointer type STRUCT task_struct must point"},
+ {"task_kfunc_release_null", "arg#0 pointer type STRUCT task_struct must point"},
+ {"task_kfunc_release_unacquired", "release kernel function bpf_task_release expects refcounted PTR_TO_BTF_ID"},
+};
+
+static void verify_fail(const char *prog_name, const char *expected_err_msg)
+{
+ LIBBPF_OPTS(bpf_object_open_opts, opts);
+ struct task_kfunc_failure *skel;
+ int err, i;
+
+ opts.kernel_log_buf = obj_log_buf;
+ opts.kernel_log_size = log_buf_sz;
+ opts.kernel_log_level = 1;
+
+ skel = task_kfunc_failure__open_opts(&opts);
+ if (!ASSERT_OK_PTR(skel, "task_kfunc_failure__open_opts"))
+ goto cleanup;
+
+ skel->bss->pid = getpid();
+
+ for (i = 0; i < ARRAY_SIZE(failure_tests); i++) {
+ struct bpf_program *prog;
+ const char *curr_name = failure_tests[i].prog_name;
+
+ prog = bpf_object__find_program_by_name(skel->obj, curr_name);
+ if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
+ goto cleanup;
+
+ bpf_program__set_autoload(prog, !strcmp(curr_name, prog_name));
+ }
+
+ err = task_kfunc_failure__load(skel);
+ if (!ASSERT_ERR(err, "unexpected load success"))
+ goto cleanup;
+
+ if (!ASSERT_OK_PTR(strstr(obj_log_buf, expected_err_msg), "expected_err_msg")) {
+ fprintf(stderr, "Expected err_msg: %s\n", expected_err_msg);
+ fprintf(stderr, "Verifier output: %s\n", obj_log_buf);
+ }
+
+cleanup:
+ task_kfunc_failure__destroy(skel);
+}
+
+void test_task_kfunc(void)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(success_tests); i++) {
+ if (!test__start_subtest(success_tests[i]))
+ continue;
+
+ run_success_test(success_tests[i]);
+ }
+
+ for (i = 0; i < ARRAY_SIZE(failure_tests); i++) {
+ if (!test__start_subtest(failure_tests[i].prog_name))
+ continue;
+
+ verify_fail(failure_tests[i].prog_name, failure_tests[i].expected_err_msg);
+ }
+}
diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_common.h b/tools/testing/selftests/bpf/progs/task_kfunc_common.h
new file mode 100644
index 000000000000..f51257bdd695
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_kfunc_common.h
@@ -0,0 +1,83 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+
+#ifndef _TASK_KFUNC_COMMON_H
+#define _TASK_KFUNC_COMMON_H
+
+#include <errno.h>
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+struct __tasks_kfunc_map_value {
+ struct task_struct __kptr_ref * task;
+};
+
+struct hash_map {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __type(key, int);
+ __type(value, struct __tasks_kfunc_map_value);
+ __uint(max_entries, 1);
+} __tasks_kfunc_map SEC(".maps");
+
+struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym;
+struct task_struct *bpf_task_kptr_get(struct task_struct **pp) __ksym;
+void bpf_task_release(struct task_struct *p) __ksym;
+
+#define TEST_NAME_SZ 128
+
+/* The pid of the test process used to determine if a newly created task is the test task. */
+int pid;
+
+static inline struct __tasks_kfunc_map_value *tasks_kfunc_map_value_lookup(struct task_struct *p)
+{
+ s32 pid;
+ long status;
+
+ status = bpf_probe_read_kernel(&pid, sizeof(pid), &p->pid);
+ if (status)
+ return NULL;
+
+ return bpf_map_lookup_elem(&__tasks_kfunc_map, &pid);
+}
+
+static inline int tasks_kfunc_map_insert(struct task_struct *p)
+{
+ struct __tasks_kfunc_map_value local, *v;
+ long status;
+ struct task_struct *acquired, *old;
+ s32 pid;
+
+ status = bpf_probe_read_kernel(&pid, sizeof(pid), &p->pid);
+ if (status)
+ return status;
+
+ local.task = NULL;
+ status = bpf_map_update_elem(&__tasks_kfunc_map, &pid, &local, BPF_NOEXIST);
+ if (status)
+ return status;
+
+ v = bpf_map_lookup_elem(&__tasks_kfunc_map, &pid);
+ if (!v) {
+ bpf_map_delete_elem(&__tasks_kfunc_map, &pid);
+ return status;
+ }
+
+ acquired = bpf_task_acquire(p);
+ old = bpf_kptr_xchg(&v->task, acquired);
+ if (old) {
+ bpf_task_release(old);
+ return -EEXIST;
+ }
+
+ return 0;
+}
+
+static inline bool is_test_kfunc_task(void)
+{
+ int cur_pid = bpf_get_current_pid_tgid() >> 32;
+
+ return pid == cur_pid;
+}
+
+#endif /* _TASK_KFUNC_COMMON_H */
diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
new file mode 100644
index 000000000000..74d2f176a2de
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
@@ -0,0 +1,315 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+#include "task_kfunc_common.h"
+
+char _license[] SEC("license") = "GPL";
+
+/* Prototype for all of the program trace events below:
+ *
+ * TRACE_EVENT(task_newtask,
+ * TP_PROTO(struct task_struct *p, u64 clone_flags)
+ */
+
+static struct __tasks_kfunc_map_value *insert_lookup_task(struct task_struct *task)
+{
+ int status;
+
+ status = tasks_kfunc_map_insert(task);
+ if (status)
+ return NULL;
+
+ return tasks_kfunc_map_value_lookup(task);
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_acquire_untrusted, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *acquired;
+ struct __tasks_kfunc_map_value *v;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ v = insert_lookup_task(task);
+ if (!v)
+ return 0;
+
+ /* Can't invoke bpf_task_acquire() on an untrusted pointer. */
+ acquired = bpf_task_acquire(v->task);
+ if (!acquired)
+ return 0;
+
+ bpf_task_release(acquired);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_acquire_fp, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *acquired, *stack_task = (struct task_struct *)&clone_flags;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ /* Can't invoke bpf_task_acquire() on a random frame pointer. */
+ acquired = bpf_task_acquire((struct task_struct *)&stack_task);
+ if (!acquired)
+ return 0;
+ bpf_task_release(acquired);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_acquire_no_null_check, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *acquired;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ acquired = bpf_task_acquire(task);
+ /* Can't release a bpf_task_acquire()'d task without a NULL check. */
+ bpf_task_release(acquired);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_acquire_trusted_nested, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *acquired;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ /* Can't invoke bpf_task_acquire() on a trusted pointer at a nonzero offset. */
+ acquired = bpf_task_acquire(task->last_wakee);
+ if (!acquired)
+ return 0;
+ bpf_task_release(acquired);
+
+ return 0;
+}
+
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_acquire_null, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *acquired;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ /* Can't invoke bpf_task_acquire() on a NULL pointer. */
+ acquired = bpf_task_acquire(NULL);
+ if (!acquired)
+ return 0;
+ bpf_task_release(acquired);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_acquire_unreleased, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *acquired;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ acquired = bpf_task_acquire(task);
+
+ /* Acquired task is never released. */
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_get_non_kptr_param, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *kptr;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ /* Cannot use bpf_task_kptr_get() on a non-kptr, even on a valid task. */
+ kptr = bpf_task_kptr_get(&task);
+ if (!kptr)
+ return 0;
+
+ bpf_task_release(kptr);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_get_non_kptr_acquired, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *kptr, *acquired;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ acquired = bpf_task_acquire(task);
+ if (!acquired)
+ return 0;
+
+ /* Cannot use bpf_task_kptr_get() on a non-kptr, even if it was acquired. */
+ kptr = bpf_task_kptr_get(&acquired);
+ bpf_task_release(acquired);
+ if (!kptr)
+ return 0;
+
+ bpf_task_release(kptr);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_get_null, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *kptr;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ /* Cannot use bpf_task_kptr_get() on a NULL pointer. */
+ kptr = bpf_task_kptr_get(NULL);
+ if (!kptr)
+ return 0;
+
+ bpf_task_release(kptr);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_xchg_unreleased, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *kptr;
+ struct __tasks_kfunc_map_value *v;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ v = insert_lookup_task(task);
+ if (!v)
+ return 0;
+
+ kptr = bpf_kptr_xchg(&v->task, NULL);
+ if (!kptr)
+ return 0;
+
+ /* Kptr retrieved from map is never released. */
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_get_unreleased, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *kptr;
+ struct __tasks_kfunc_map_value *v;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ v = insert_lookup_task(task);
+ if (!v)
+ return 0;
+
+ kptr = bpf_task_kptr_get(&v->task);
+ if (!kptr)
+ return 0;
+
+ /* Kptr acquired above is never released. */
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_release_untrusted, struct task_struct *task, u64 clone_flags)
+{
+ struct __tasks_kfunc_map_value *v;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ v = insert_lookup_task(task);
+ if (!v)
+ return 0;
+
+ /* Can't invoke bpf_task_release() on an untrusted pointer. */
+ bpf_task_release(v->task);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_release_fp, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *acquired = (struct task_struct *)&clone_flags;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ /* Cannot release random frame pointer. */
+ bpf_task_release(acquired);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_release_null, struct task_struct *task, u64 clone_flags)
+{
+ struct __tasks_kfunc_map_value local, *v;
+ long status;
+ struct task_struct *acquired, *old;
+ s32 pid;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ status = bpf_probe_read_kernel(&pid, sizeof(pid), &task->pid);
+ if (status)
+ return 0;
+
+ local.task = NULL;
+ status = bpf_map_update_elem(&__tasks_kfunc_map, &pid, &local, BPF_NOEXIST);
+ if (status)
+ return status;
+
+ v = bpf_map_lookup_elem(&__tasks_kfunc_map, &pid);
+ if (!v)
+ return status;
+
+ acquired = bpf_task_acquire(task);
+ if (!acquired)
+ return 0;
+
+ old = bpf_kptr_xchg(&v->task, acquired);
+
+ /* old cannot be passed to bpf_task_release() without a NULL check. */
+ bpf_task_release(old);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(task_kfunc_release_unacquired, struct task_struct *task, u64 clone_flags)
+{
+ if (!is_test_kfunc_task())
+ return 0;
+
+ /* Cannot release trusted task pointer which was not acquired. */
+ bpf_task_release(task);
+
+ return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_success.c b/tools/testing/selftests/bpf/progs/task_kfunc_success.c
new file mode 100644
index 000000000000..8d5c05b41d53
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_kfunc_success.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+#include "task_kfunc_common.h"
+
+char _license[] SEC("license") = "GPL";
+
+int err;
+
+/* Prototype for all of the program trace events below:
+ *
+ * TRACE_EVENT(task_newtask,
+ * TP_PROTO(struct task_struct *p, u64 clone_flags)
+ */
+
+static int test_acquire_release(struct task_struct *task)
+{
+ struct task_struct *acquired;
+
+ acquired = bpf_task_acquire(task);
+ if (!acquired) {
+ err = 1;
+ return 0;
+ }
+
+ bpf_task_release(acquired);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(test_task_acquire_release_argument, struct task_struct *task, u64 clone_flags)
+{
+ if (!is_test_kfunc_task())
+ return 0;
+
+ return test_acquire_release(task);
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(test_task_acquire_release_current, struct task_struct *task, u64 clone_flags)
+{
+ if (!is_test_kfunc_task())
+ return 0;
+
+ return test_acquire_release(bpf_get_current_task_btf());
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(test_task_acquire_leave_in_map, struct task_struct *task, u64 clone_flags)
+{
+ long status;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ status = tasks_kfunc_map_insert(task);
+ if (status)
+ err = 1;
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(test_task_xchg_release, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *kptr;
+ struct __tasks_kfunc_map_value *v;
+ long status;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ status = tasks_kfunc_map_insert(task);
+ if (status) {
+ err = 1;
+ return 0;
+ }
+
+ v = tasks_kfunc_map_value_lookup(task);
+ if (!v) {
+ err = 2;
+ return 0;
+ }
+
+ kptr = bpf_kptr_xchg(&v->task, NULL);
+ if (!kptr) {
+ err = 3;
+ return 0;
+ }
+
+ bpf_task_release(kptr);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(test_task_get_release, struct task_struct *task, u64 clone_flags)
+{
+ struct task_struct *kptr;
+ struct __tasks_kfunc_map_value *v;
+ long status;
+
+ if (!is_test_kfunc_task())
+ return 0;
+
+ status = tasks_kfunc_map_insert(task);
+ if (status) {
+ err = 1;
+ return 0;
+ }
+
+ v = tasks_kfunc_map_value_lookup(task);
+ if (!v) {
+ err = 2;
+ return 0;
+ }
+
+ kptr = bpf_task_kptr_get(&v->task);
+ if (!kptr) {
+ err = 3;
+ return 0;
+ }
+
+ bpf_task_release(kptr);
+
+ return 0;
+}
--
2.38.0
On Fri, Oct 14, 2022 at 03:14:25PM -0500, David Vernet wrote:
[...]
> @@ -5768,6 +5778,9 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
> if (arg_type & PTR_MAYBE_NULL)
> type &= ~PTR_MAYBE_NULL;
>
> + if (!(arg_type & ARG_PTR_TO_BTF_ID))
> + type &= ~PTR_NESTED;
> +
Argh, I added while debugging something and I meant to remove it before
sending out the next version. I'll send out v4 shortly without this,
apologies for the noise.
On Sat, 15 Oct 2022 at 01:45, David Vernet <[email protected]> wrote:
>
> A previous change added a series of kfuncs for storing struct
> task_struct objects as referenced kptrs. This patch adds a new
> task_kfunc test suite for validating their expected behavior.
>
> Signed-off-by: David Vernet <[email protected]>
> ---
> [...]
> +
> +SEC("tp_btf/task_newtask")
> +int BPF_PROG(task_kfunc_acquire_trusted_nested, struct task_struct *task, u64 clone_flags)
> +{
> + struct task_struct *acquired;
> +
> + if (!is_test_kfunc_task())
> + return 0;
> +
> + /* Can't invoke bpf_task_acquire() on a trusted pointer at a nonzero offset. */
> + acquired = bpf_task_acquire(task->last_wakee);
The comment is incorrect, that would be &task->last_wakee instead,
this is PTR_TO_BTF_ID | PTR_NESTED.
> + if (!acquired)
> + return 0;
> + bpf_task_release(acquired);
> +
> + return 0;
> +}
> +
> [...]
> +
> +static int test_acquire_release(struct task_struct *task)
> +{
> + struct task_struct *acquired;
> +
> + acquired = bpf_task_acquire(task);
Unfortunately a side effect of this change is that now since
PTR_TO_BTF_ID without ref_obj_id is considered trusted, the bpf_ct_*
functions would begin working with tp_btf args. That probably needs to
be fixed so that they reject them (ideally with a failing test case to
make sure it doesn't resurface), probably with a new suffix __ref/or
__owned as added here [0].
Alexei, since you've suggested avoiding adding that suffix, do you see
any other way out here?
It's questionable whether bpf_ct_set_timeout/status should work for CT
not owned by the BPF program.
[0]: https://lore.kernel.org/bpf/dfb859a6b76a9234baa194e795ae89cb7ca5694b.1662383493.git.lorenzo@kernel.org
> + if (!acquired) {
> + err = 1;
> + return 0;
> + }
> +
> + bpf_task_release(acquired);
> +
> + return 0;
> +}
> +
> [...]
On Tue, 18 Oct 2022 at 07:23, Kumar Kartikeya Dwivedi <[email protected]> wrote:
>
> On Sat, 15 Oct 2022 at 01:45, David Vernet <[email protected]> wrote:
> >
> > A previous change added a series of kfuncs for storing struct
> > task_struct objects as referenced kptrs. This patch adds a new
> > task_kfunc test suite for validating their expected behavior.
> >
> > Signed-off-by: David Vernet <[email protected]>
> > ---
> > [...]
> > +
> > +SEC("tp_btf/task_newtask")
> > +int BPF_PROG(task_kfunc_acquire_trusted_nested, struct task_struct *task, u64 clone_flags)
> > +{
> > + struct task_struct *acquired;
> > +
> > + if (!is_test_kfunc_task())
> > + return 0;
> > +
> > + /* Can't invoke bpf_task_acquire() on a trusted pointer at a nonzero offset. */
> > + acquired = bpf_task_acquire(task->last_wakee);
>
> The comment is incorrect, that would be &task->last_wakee instead,
> this is PTR_TO_BTF_ID | PTR_NESTED.
>
> > + if (!acquired)
> > + return 0;
> > + bpf_task_release(acquired);
> > +
> > + return 0;
> > +}
> > +
> > [...]
> > +
> > +static int test_acquire_release(struct task_struct *task)
> > +{
> > + struct task_struct *acquired;
> > +
> > + acquired = bpf_task_acquire(task);
>
> Unfortunately a side effect of this change is that now since
> PTR_TO_BTF_ID without ref_obj_id is considered trusted, the bpf_ct_*
> functions would begin working with tp_btf args. That probably needs to
> be fixed so that they reject them (ideally with a failing test case to
> make sure it doesn't resurface), probably with a new suffix __ref/or
> __owned as added here [0].
>
> Alexei, since you've suggested avoiding adding that suffix, do you see
> any other way out here?
> It's questionable whether bpf_ct_set_timeout/status should work for CT
> not owned by the BPF program.
>
> [0]: https://lore.kernel.org/bpf/dfb859a6b76a9234baa194e795ae89cb7ca5694b.1662383493.git.lorenzo@kernel.org
>
Sorry for accidentally bumping this v3 thread instead of v5, whosoever
replies please continue there.