From 6c831c4684124a544f73f7c9b83bc7b2eb0b23d3 Mon Sep 17 00:00:00 2001 From: David Vernet Date: Sat, 25 Mar 2023 16:31:46 -0500 Subject: [PATCH] bpf: Treat KF_RELEASE kfuncs as KF_TRUSTED_ARGS KF_RELEASE kfuncs are not currently treated as having KF_TRUSTED_ARGS, even though they have a superset of the requirements of KF_TRUSTED_ARGS. Like KF_TRUSTED_ARGS, KF_RELEASE kfuncs require a 0-offset argument, and don't allow NULL-able arguments. Unlike KF_TRUSTED_ARGS which require _either_ an argument with ref_obj_id > 0, _or_ (ref->type & BPF_REG_TRUSTED_MODIFIERS) (and no unsafe modifiers allowed), KF_RELEASE only allows for ref_obj_id > 0. Because KF_RELEASE today doesn't automatically imply KF_TRUSTED_ARGS, some of these requirements are enforced in different ways that can make the behavior of the verifier feel unpredictable. For example, a KF_RELEASE kfunc with a NULL-able argument will currently fail in the verifier with a message like, "arg#0 is ptr_or_null_ expected ptr_ or socket" rather than "Possibly NULL pointer passed to trusted arg0". Our intention is the same, but the semantics are different due to implemenetation details that kfunc authors and BPF program writers should not need to care about. Let's make the behavior of the verifier more consistent and intuitive by having KF_RELEASE kfuncs imply the presence of KF_TRUSTED_ARGS. Our eventual goal is to have all kfuncs assume KF_TRUSTED_ARGS by default anyways, so this takes us a step in that direction. Note that it does not make sense to assume KF_TRUSTED_ARGS for all KF_ACQUIRE kfuncs. KF_ACQUIRE kfuncs can have looser semantics than KF_RELEASE, with e.g. KF_RCU | KF_RET_NULL. We may want to have KF_ACQUIRE imply KF_TRUSTED_ARGS _unless_ KF_RCU is specified, but that can be left to another patch set, and there are no such subtleties to address for KF_RELEASE. Signed-off-by: David Vernet Link: https://lore.kernel.org/r/20230325213144.486885-4-void@manifault.com Signed-off-by: Alexei Starovoitov --- Documentation/bpf/kfuncs.rst | 7 ++++--- kernel/bpf/cpumask.c | 2 +- kernel/bpf/verifier.c | 2 +- net/bpf/test_run.c | 6 ++++++ tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c | 4 ++-- tools/testing/selftests/bpf/progs/task_kfunc_failure.c | 6 +++--- tools/testing/selftests/bpf/verifier/calls.c | 10 +++++++--- tools/testing/selftests/bpf/verifier/ref_tracking.c | 6 +++--- 8 files changed, 27 insertions(+), 16 deletions(-) diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst index 69eccf6..bf1b859 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -179,9 +179,10 @@ both are orthogonal to each other. --------------------- The KF_RELEASE flag is used to indicate that the kfunc releases the pointer -passed in to it. There can be only one referenced pointer that can be passed in. -All copies of the pointer being released are invalidated as a result of invoking -kfunc with this flag. +passed in to it. There can be only one referenced pointer that can be passed +in. All copies of the pointer being released are invalidated as a result of +invoking kfunc with this flag. KF_RELEASE kfuncs automatically receive the +protection afforded by the KF_TRUSTED_ARGS flag described below. 2.4.4 KF_KPTR_GET flag ---------------------- diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c index e991af7..7efdf5d 100644 --- a/kernel/bpf/cpumask.c +++ b/kernel/bpf/cpumask.c @@ -402,7 +402,7 @@ __diag_pop(); BTF_SET8_START(cpumask_kfunc_btf_ids) BTF_ID_FLAGS(func, bpf_cpumask_create, KF_ACQUIRE | KF_RET_NULL) -BTF_ID_FLAGS(func, bpf_cpumask_release, KF_RELEASE | KF_TRUSTED_ARGS) +BTF_ID_FLAGS(func, bpf_cpumask_release, KF_RELEASE) BTF_ID_FLAGS(func, bpf_cpumask_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS) BTF_ID_FLAGS(func, bpf_cpumask_first, KF_RCU) BTF_ID_FLAGS(func, bpf_cpumask_first_zero, KF_RCU) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 64f06f6..20eb201 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9307,7 +9307,7 @@ static bool is_kfunc_release(struct bpf_kfunc_call_arg_meta *meta) static bool is_kfunc_trusted_args(struct bpf_kfunc_call_arg_meta *meta) { - return meta->kfunc_flags & KF_TRUSTED_ARGS; + return (meta->kfunc_flags & KF_TRUSTED_ARGS) || is_kfunc_release(meta); } static bool is_kfunc_sleepable(struct bpf_kfunc_call_arg_meta *meta) diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 27587f1..f1652f5 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -606,6 +606,11 @@ bpf_kfunc_call_test_acquire(unsigned long *scalar_ptr) return &prog_test_struct; } +__bpf_kfunc void bpf_kfunc_call_test_offset(struct prog_test_ref_kfunc *p) +{ + WARN_ON_ONCE(1); +} + __bpf_kfunc struct prog_test_member * bpf_kfunc_call_memb_acquire(void) { @@ -800,6 +805,7 @@ BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail2) BTF_ID_FLAGS(func, bpf_kfunc_call_test_ref, KF_TRUSTED_ARGS | KF_RCU) BTF_ID_FLAGS(func, bpf_kfunc_call_test_destructive, KF_DESTRUCTIVE) BTF_ID_FLAGS(func, bpf_kfunc_call_test_static_unused_arg) +BTF_ID_FLAGS(func, bpf_kfunc_call_test_offset) BTF_SET8_END(test_sk_check_kfunc_ids) static void *bpf_test_init(const union bpf_attr *kattr, u32 user_size, diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c b/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c index 807fb0a..48b2034 100644 --- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c +++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c @@ -206,7 +206,7 @@ int BPF_PROG(cgrp_kfunc_get_unreleased, struct cgroup *cgrp, const char *path) } SEC("tp_btf/cgroup_mkdir") -__failure __msg("expects refcounted") +__failure __msg("Possibly NULL pointer passed to trusted arg0") int BPF_PROG(cgrp_kfunc_release_untrusted, struct cgroup *cgrp, const char *path) { struct __cgrps_kfunc_map_value *v; @@ -234,7 +234,7 @@ int BPF_PROG(cgrp_kfunc_release_fp, struct cgroup *cgrp, const char *path) } SEC("tp_btf/cgroup_mkdir") -__failure __msg("arg#0 is ptr_or_null_ expected ptr_ or socket") +__failure __msg("Possibly NULL pointer passed to trusted arg0") int BPF_PROG(cgrp_kfunc_release_null, struct cgroup *cgrp, const char *path) { struct __cgrps_kfunc_map_value local, *v; diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c index 27994d6..2c374a7 100644 --- a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c +++ b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c @@ -206,7 +206,7 @@ int BPF_PROG(task_kfunc_get_unreleased, struct task_struct *task, u64 clone_flag } SEC("tp_btf/task_newtask") -__failure __msg("arg#0 is untrusted_ptr_or_null_ expected ptr_ or socket") +__failure __msg("Possibly NULL pointer passed to trusted arg0") int BPF_PROG(task_kfunc_release_untrusted, struct task_struct *task, u64 clone_flags) { struct __tasks_kfunc_map_value *v; @@ -234,7 +234,7 @@ int BPF_PROG(task_kfunc_release_fp, struct task_struct *task, u64 clone_flags) } SEC("tp_btf/task_newtask") -__failure __msg("arg#0 is ptr_or_null_ expected ptr_ or socket") +__failure __msg("Possibly NULL pointer passed to trusted arg0") int BPF_PROG(task_kfunc_release_null, struct task_struct *task, u64 clone_flags) { struct __tasks_kfunc_map_value local, *v; @@ -277,7 +277,7 @@ int BPF_PROG(task_kfunc_release_unacquired, struct task_struct *task, u64 clone_ } SEC("tp_btf/task_newtask") -__failure __msg("arg#0 is ptr_or_null_ expected ptr_ or socket") +__failure __msg("Possibly NULL pointer passed to trusted arg0") int BPF_PROG(task_kfunc_from_pid_no_null_check, struct task_struct *task, u64 clone_flags) { struct task_struct *acquired; diff --git a/tools/testing/selftests/bpf/verifier/calls.c b/tools/testing/selftests/bpf/verifier/calls.c index 5702fc9..1bdf2b4 100644 --- a/tools/testing/selftests/bpf/verifier/calls.c +++ b/tools/testing/selftests/bpf/verifier/calls.c @@ -109,7 +109,7 @@ }, .prog_type = BPF_PROG_TYPE_SCHED_CLS, .result = REJECT, - .errstr = "arg#0 is ptr_or_null_ expected ptr_ or socket", + .errstr = "Possibly NULL pointer passed to trusted arg0", .fixup_kfunc_btf_id = { { "bpf_kfunc_call_test_acquire", 3 }, { "bpf_kfunc_call_test_release", 5 }, @@ -165,19 +165,23 @@ BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8), BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 0), BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0), + BPF_MOV64_REG(BPF_REG_2, BPF_REG_0), BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1), BPF_EXIT_INSN(), BPF_MOV64_REG(BPF_REG_1, BPF_REG_0), - BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1, 16), BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -4), BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0), BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_MOV64_REG(BPF_REG_1, BPF_REG_2), + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0), + BPF_MOV64_IMM(BPF_REG_0, 0), BPF_EXIT_INSN(), }, .prog_type = BPF_PROG_TYPE_SCHED_CLS, .fixup_kfunc_btf_id = { { "bpf_kfunc_call_test_acquire", 3 }, - { "bpf_kfunc_call_test_release", 9 }, + { "bpf_kfunc_call_test_offset", 9 }, + { "bpf_kfunc_call_test_release", 12 }, }, .result_unpriv = REJECT, .result = REJECT, diff --git a/tools/testing/selftests/bpf/verifier/ref_tracking.c b/tools/testing/selftests/bpf/verifier/ref_tracking.c index 9540164..5a2e154 100644 --- a/tools/testing/selftests/bpf/verifier/ref_tracking.c +++ b/tools/testing/selftests/bpf/verifier/ref_tracking.c @@ -142,7 +142,7 @@ .kfunc = "bpf", .expected_attach_type = BPF_LSM_MAC, .flags = BPF_F_SLEEPABLE, - .errstr = "arg#0 is ptr_or_null_ expected ptr_ or socket", + .errstr = "Possibly NULL pointer passed to trusted arg0", .fixup_kfunc_btf_id = { { "bpf_lookup_user_key", 2 }, { "bpf_key_put", 4 }, @@ -163,7 +163,7 @@ .kfunc = "bpf", .expected_attach_type = BPF_LSM_MAC, .flags = BPF_F_SLEEPABLE, - .errstr = "arg#0 is ptr_or_null_ expected ptr_ or socket", + .errstr = "Possibly NULL pointer passed to trusted arg0", .fixup_kfunc_btf_id = { { "bpf_lookup_system_key", 1 }, { "bpf_key_put", 3 }, @@ -182,7 +182,7 @@ .kfunc = "bpf", .expected_attach_type = BPF_LSM_MAC, .flags = BPF_F_SLEEPABLE, - .errstr = "arg#0 pointer type STRUCT bpf_key must point to scalar, or struct with scalar", + .errstr = "Possibly NULL pointer passed to trusted arg0", .fixup_kfunc_btf_id = { { "bpf_key_put", 1 }, }, -- 2.7.4