Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   David Vernet <void@manifault.com>
To:     bpf@vger.kernel.org
Cc:     ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net,
        martin.lau@linux.dev, memxor@gmail.com, yhs@fb.com,
        song@kernel.org, sdf@google.com, john.fastabend@gmail.com,
        kpsingh@kernel.org, jolsa@kernel.org, haoluo@google.com,
        tj@kernel.org, kernel-team@fb.com, linux-kernel@vger.kernel.org
Subject: [PATCH bpf-next v7 1/3] bpf: Allow trusted pointers to be passed to KF_TRUSTED_ARGS kfuncs
Date:   Wed, 16 Nov 2022 21:24:00 -0600
Message-Id: <20221117032402.2356776-2-void@manifault.com>
In-Reply-To: <20221117032402.2356776-1-void@manifault.com>
References: <20221117032402.2356776-1-void@manifault.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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_TRUSTED
which tracks whether a PTR_TO_BTF_ID pointer is safe to pass to a
KF_TRUSTED_ARGS kfunc or a BPF helper function. PTR_TRUSTED pointers are
passed directly from the kernel as a tracepoint or struct_ops callback
argument. Any nested pointer that is obtained from walking a PTR_TRUSTED
pointer is no longer PTR_TRUSTED. From the example above, the struct
task_struct *task argument is PTR_TRUSTED, but the 'nested' pointer
obtained from 'task->last_wakee' is not PTR_TRUSTED.

A subsequent patch will add kfuncs for storing a task kfunc as a kptr,
and then another patch will add selftests to validate.

Signed-off-by: David Vernet <void@manifault.com>
---
 Documentation/bpf/kfuncs.rst                  | 30 ++++-----
 include/linux/bpf.h                           | 30 +++++++++
 include/linux/btf.h                           | 65 ++++++++++++-------
 kernel/bpf/btf.c                              | 38 +++++++++--
 kernel/bpf/verifier.c                         | 45 ++++++++-----
 kernel/trace/bpf_trace.c                      |  2 +-
 net/ipv4/bpf_tcp_ca.c                         |  4 +-
 tools/testing/selftests/bpf/verifier/calls.c  |  2 +-
 .../selftests/bpf/verifier/ref_tracking.c     |  4 +-
 9 files changed, 154 insertions(+), 66 deletions(-)

diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
index 0f858156371d..67b7e2f46ec6 100644
--- a/Documentation/bpf/kfuncs.rst
+++ b/Documentation/bpf/kfuncs.rst
@@ -137,22 +137,20 @@ KF_ACQUIRE and KF_RET_NULL flags.
 --------------------------
 
 The KF_TRUSTED_ARGS flag is used for kfuncs taking pointer arguments. It
-indicates that the all pointer arguments will always have a guaranteed lifetime,
-and pointers to kernel objects are always passed to helpers in their unmodified
-form (as obtained from acquire kfuncs).
-
-It can be used to enforce that a pointer to a refcounted object acquired from a
-kfunc or BPF helper is passed as an argument to this kfunc without any
-modifications (e.g. pointer arithmetic) such that it is trusted and points to
-the original object.
-
-Meanwhile, it is also allowed pass pointers to normal memory to such kfuncs,
-but those can have a non-zero offset.
-
-This flag is often used for kfuncs that operate (change some property, perform
-some operation) on an object that was obtained using an acquire kfunc. Such
-kfuncs need an unchanged pointer to ensure the integrity of the operation being
-performed on the expected object.
+indicates that the all pointer arguments are valid, and that all pointers to
+BTF objects have been passed in their unmodified form (that is, at a zero
+offset, and without having been obtained from walking another pointer).
+
+There are two types of pointers to kernel objects which are considered "valid":
+
+1. Pointers which are passed as tracepoint or struct_ops callback arguments.
+2. Pointers which were returned from a KF_ACQUIRE or KF_KPTR_GET kfunc.
+
+Pointers to non-BTF objects (e.g. scalar pointers) may also be passed to
+KF_TRUSTED_ARGS kfuncs, and may have a non-zero offset.
+
+The definition of "valid" pointers is subject to change at any time, and has
+absolutely no ABI stability guarantees.
 
 2.4.6 KF_SLEEPABLE flag
 -----------------------
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 54462dd28824..763ae250693e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -524,6 +524,35 @@ enum bpf_type_flag {
 	/* Size is known at compile time. */
 	MEM_FIXED_SIZE		= BIT(10 + BPF_BASE_TYPE_BITS),
 
+	/* PTR was passed from the kernel in a trusted context, and may be
+	 * passed to KF_TRUSTED_ARGS kfuncs or BPF helper functions.
+	 * Confusingly, this is _not_ the opposite of PTR_UNTRUSTED above.
+	 * PTR_UNTRUSTED refers to a kptr that was read directly from a map
+	 * without invoking bpf_kptr_xchg(). What we really need to know is
+	 * whether a pointer is safe to pass to a kfunc or BPF helper function.
+	 * While PTR_UNTRUSTED pointers are unsafe to pass to kfuncs and BPF
+	 * helpers, they do not cover all possible instances of unsafe
+	 * pointers. For example, a pointer that was obtained from walking a
+	 * struct will _not_ get the PTR_UNTRUSTED type modifier, despite the
+	 * fact that it may be NULL, invalid, etc. This is due to backwards
+	 * compatibility requirements, as this was the behavior that was first
+	 * introduced when kptrs were added. The behavior is now considered
+	 * deprecated, and PTR_UNTRUSTED will eventually be removed.
+	 *
+	 * PTR_TRUSTED, on the other hand, is a pointer that the kernel
+	 * guarantees to be valid and safe to pass to kfuncs and BPF helpers.
+	 * For example, pointers passed to tracepoint arguments are considered
+	 * PTR_TRUSTED, as are pointers that are passed to struct_ops
+	 * callbacks. As alluded to above, pointers that are obtained from
+	 * walking PTR_TRUSTED pointers are _not_ trusted. For example, if a
+	 * struct task_struct *task is PTR_TRUSTED, then accessing
+	 * task->last_wakee will lose the PTR_TRUSTED modifier when it's stored
+	 * in a BPF register. Similarly, pointers passed to certain programs
+	 * types such as kretprobes are not guaranteed to be valid, as they may
+	 * for example contain an object that was recently freed.
+	 */
+	PTR_TRUSTED		= BIT(11 + BPF_BASE_TYPE_BITS),
+
 	__BPF_TYPE_FLAG_MAX,
 	__BPF_TYPE_LAST_FLAG	= __BPF_TYPE_FLAG_MAX - 1,
 };
@@ -617,6 +646,7 @@ enum bpf_return_type {
 	RET_PTR_TO_RINGBUF_MEM_OR_NULL	= PTR_MAYBE_NULL | MEM_RINGBUF | RET_PTR_TO_MEM,
 	RET_PTR_TO_DYNPTR_MEM_OR_NULL	= PTR_MAYBE_NULL | RET_PTR_TO_MEM,
 	RET_PTR_TO_BTF_ID_OR_NULL	= PTR_MAYBE_NULL | RET_PTR_TO_BTF_ID,
+	RET_PTR_TO_BTF_ID_TRUSTED	= PTR_TRUSTED	 | RET_PTR_TO_BTF_ID,
 
 	/* This must be the last entry. Its purpose is to ensure the enum is
 	 * wide enough to hold the higher bits reserved for bpf_type_flag.
diff --git a/include/linux/btf.h b/include/linux/btf.h
index d80345fa566b..13b969e74d3b 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -17,36 +17,53 @@
 #define KF_RELEASE	(1 << 1) /* kfunc is a release function */
 #define KF_RET_NULL	(1 << 2) /* kfunc returns a pointer that may be NULL */
 #define KF_KPTR_GET	(1 << 3) /* kfunc returns reference to a kptr */
-/* Trusted arguments are those which are meant to be referenced arguments with
- * unchanged offset. It is used to enforce that pointers obtained from acquire
- * kfuncs remain unmodified when being passed to helpers taking trusted args.
+/* Trusted arguments are those which are guaranteed to be valid when passed to
+ * the kfunc. It is used to enforce that pointers obtained from either acquire
+ * kfuncs, or from the main kernel on a tracepoint or struct_ops callback
+ * invocation, remain unmodified when being passed to helpers taking trusted
+ * args.
  *
- * Consider
- *	struct foo {
- *		int data;
- *		struct foo *next;
- *	};
+ * Consider, for example, the following new task tracepoint:
  *
- *	struct bar {
- *		int data;
- *		struct foo f;
- *	};
+ *	SEC("tp_btf/task_newtask")
+ *	int BPF_PROG(new_task_tp, struct task_struct *task, u64 clone_flags)
+ *	{
+ *		...
+ *	}
  *
- *	struct foo *f = alloc_foo(); // Acquire kfunc
- *	struct bar *b = alloc_bar(); // Acquire kfunc
+ * And the following kfunc:
  *
- * If a kfunc set_foo_data() wants to operate only on the allocated object, it
- * will set the KF_TRUSTED_ARGS flag, which will prevent unsafe usage like:
+ *	BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
  *
- *	set_foo_data(f, 42);	   // Allowed
- *	set_foo_data(f->next, 42); // Rejected, non-referenced pointer
- *	set_foo_data(&f->next, 42);// Rejected, referenced, but wrong type
- *	set_foo_data(&b->f, 42);   // Rejected, referenced, but bad offset
+ * All invocations to the kfunc must pass the unmodified, unwalked task:
  *
- * In the final case, usually for the purposes of type matching, it is deduced
- * by looking at the type of the member at the offset, but due to the
- * requirement of trusted argument, this deduction will be strict and not done
- * for this case.
+ *	bpf_task_acquire(task);		    // Allowed
+ *	bpf_task_acquire(task->last_wakee); // Rejected, walked task
+ *
+ * Programs may also pass referenced tasks directly to the kfunc:
+ *
+ *	struct task_struct *acquired;
+ *
+ *	acquired = bpf_task_acquire(task);	// Allowed, same as above
+ *	bpf_task_acquire(acquired);		// Allowed
+ *	bpf_task_acquire(task);			// Allowed
+ *	bpf_task_acquire(acquired->last_wakee); // Rejected, walked task
+ *
+ * Programs may _not_, however, pass a task from an arbitrary fentry/fexit, or
+ * kprobe/kretprobe to the kfunc, as BPF cannot guarantee that all of these
+ * pointers are guaranteed to be safe. For example, the following BPF program
+ * would be rejected:
+ *
+ * SEC("kretprobe/free_task")
+ * int BPF_PROG(free_task_probe, struct task_struct *tsk)
+ * {
+ *	struct task_struct *acquired;
+ *
+ *	acquired = bpf_task_acquire(acquired); // Rejected, not a trusted pointer
+ *	bpf_task_release(acquired);
+ *
+ *	return 0;
+ * }
  */
 #define KF_TRUSTED_ARGS (1 << 4) /* kfunc only takes trusted pointer arguments */
 #define KF_SLEEPABLE    (1 << 5) /* kfunc may sleep */
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 875355ff3718..8291f2911624 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5579,6 +5579,11 @@ static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type *func_proto,
 	return nr_args + 1;
 }
 
+static bool prog_type_args_trusted(enum bpf_prog_type prog_type)
+{
+	return prog_type == BPF_PROG_TYPE_TRACING || prog_type == BPF_PROG_TYPE_STRUCT_OPS;
+}
+
 bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 		    const struct bpf_prog *prog,
 		    struct bpf_insn_access_aux *info)
@@ -5722,6 +5727,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 	}
 
 	info->reg_type = PTR_TO_BTF_ID;
+	if (prog_type_args_trusted(prog->type))
+		info->reg_type |= PTR_TRUSTED;
+
 	if (tgt_prog) {
 		enum bpf_prog_type tgt_type;
 
@@ -6558,15 +6566,26 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 		/* These register types have special constraints wrt ref_obj_id
 		 * and offset checks. The rest of trusted args don't.
 		 */
-		obj_ptr = reg->type == PTR_TO_CTX || reg->type == PTR_TO_BTF_ID ||
+		obj_ptr = reg->type == PTR_TO_CTX ||
+			  base_type(reg->type) == PTR_TO_BTF_ID ||
 			  reg2btf_ids[base_type(reg->type)];
 
 		/* 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
+		 * - PTR_TRUSTED pointers
 		 */
-		if (is_kfunc && trusted_args && (obj_ptr && reg->type != PTR_TO_CTX) && !reg->ref_obj_id) {
-			bpf_log(log, "R%d must be referenced\n", regno);
+		if (is_kfunc &&
+		    trusted_args &&
+		    obj_ptr &&
+		    base_type(reg->type) != PTR_TO_CTX &&
+		    (!(type_flag(reg->type) & PTR_TRUSTED) ||
+		     (type_flag(reg->type) & ~PTR_TRUSTED)) &&
+		    !reg->ref_obj_id) {
+			bpf_log(log, "R%d must be referenced or trusted\n", regno);
 			return -EINVAL;
 		}
 
@@ -6646,8 +6665,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 					i, btf_type_str(t));
 				return -EINVAL;
 			}
-		} else if (is_kfunc && (reg->type == PTR_TO_BTF_ID ||
-			   (reg2btf_ids[base_type(reg->type)] && !type_flag(reg->type)))) {
+		} else if (is_kfunc && (base_type(reg->type) == PTR_TO_BTF_ID ||
+			   (reg2btf_ids[base_type(reg->type)]))) {
 			const struct btf_type *reg_ref_t;
 			const struct btf *reg_btf;
 			const char *reg_ref_tname;
@@ -6660,7 +6679,13 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 				return -EINVAL;
 			}
 
-			if (reg->type == PTR_TO_BTF_ID) {
+			if ((type_flag(reg->type) & ~PTR_TRUSTED)) {
+				bpf_log(log, "kernel function %s arg#%d pointer had unexpected modifiers %d\n",
+					func_name, i, type_flag(reg->type));
+				return -EINVAL;
+			}
+
+			if (base_type(reg->type) == PTR_TO_BTF_ID) {
 				reg_btf = reg->btf;
 				reg_ref_id = reg->btf_id;
 			} else {
@@ -6988,6 +7013,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
 			}
 
 			reg->type = PTR_TO_MEM | PTR_MAYBE_NULL;
+
 			reg->id = ++env->id_gen;
 
 			continue;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0312d9ce292f..f5b6b1f969d9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -543,7 +543,7 @@ static bool is_cmpxchg_insn(const struct bpf_insn *insn)
 static const char *reg_type_str(struct bpf_verifier_env *env,
 				enum bpf_reg_type type)
 {
-	char postfix[16] = {0}, prefix[32] = {0};
+	char postfix[16] = {0}, prefix[64] = {0};
 	static const char * const str[] = {
 		[NOT_INIT]		= "?",
 		[SCALAR_VALUE]		= "scalar",
@@ -575,16 +575,14 @@ static const char *reg_type_str(struct bpf_verifier_env *env,
 			strncpy(postfix, "_or_null", 16);
 	}
 
-	if (type & MEM_RDONLY)
-		strncpy(prefix, "rdonly_", 32);
-	if (type & MEM_RINGBUF)
-		strncpy(prefix, "ringbuf_", 32);
-	if (type & MEM_USER)
-		strncpy(prefix, "user_", 32);
-	if (type & MEM_PERCPU)
-		strncpy(prefix, "percpu_", 32);
-	if (type & PTR_UNTRUSTED)
-		strncpy(prefix, "untrusted_", 32);
+	snprintf(prefix, sizeof(prefix), "%s%s%s%s%s%s",
+		 type & MEM_RDONLY ? "rdonly_" : "",
+		 type & MEM_RINGBUF ? "ringbuf_" : "",
+		 type & MEM_USER ? "user_" : "",
+		 type & MEM_PERCPU ? "percpu_" : "",
+		 type & PTR_UNTRUSTED ? "untrusted_" : "",
+		 type & PTR_TRUSTED ? "trusted_" : ""
+	);
 
 	snprintf(env->type_str_buf, TYPE_STR_BUF_LEN, "%s%s%s",
 		 prefix, str[base_type(type)], postfix);
@@ -3844,7 +3842,7 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
 			       struct bpf_reg_state *reg, u32 regno)
 {
 	const char *targ_name = kernel_type_name(kptr_field->kptr.btf, kptr_field->kptr.btf_id);
-	int perm_flags = PTR_MAYBE_NULL;
+	int perm_flags = PTR_MAYBE_NULL | PTR_TRUSTED;
 	const char *reg_name = "";
 
 	/* Only unreferenced case accepts untrusted pointers */
@@ -4707,6 +4705,9 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
 	if (type_flag(reg->type) & PTR_UNTRUSTED)
 		flag |= PTR_UNTRUSTED;
 
+	/* Any pointer obtained from walking a trusted pointer is no longer trusted. */
+	flag &= ~PTR_TRUSTED;
+
 	if (atype == BPF_READ && value_regno >= 0)
 		mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id, flag);
 
@@ -5774,6 +5775,7 @@ static const struct bpf_reg_types btf_id_sock_common_types = {
 		PTR_TO_TCP_SOCK,
 		PTR_TO_XDP_SOCK,
 		PTR_TO_BTF_ID,
+		PTR_TO_BTF_ID | PTR_TRUSTED,
 	},
 	.btf_id = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
 };
@@ -5807,9 +5809,19 @@ 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 ringbuf_mem_types = { .types = { PTR_TO_MEM | MEM_RINGBUF } };
 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_TRUSTED,
+	},
+};
 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 percpu_btf_ptr_types = {
+	.types = {
+		PTR_TO_BTF_ID | MEM_PERCPU,
+		PTR_TO_BTF_ID | MEM_PERCPU | PTR_TRUSTED,
+	}
+};
 static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC } };
 static const struct bpf_reg_types stack_ptr_types = { .types = { PTR_TO_STACK } };
 static const struct bpf_reg_types const_str_ptr_types = { .types = { PTR_TO_MAP_VALUE } };
@@ -5897,7 +5909,7 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 	return -EACCES;
 
 found:
-	if (reg->type == PTR_TO_BTF_ID) {
+	if (base_type(reg->type) == PTR_TO_BTF_ID && !(type_flag(reg->type) & ~PTR_TRUSTED)) {
 		/* For bpf_sk_release, it needs to match against first member
 		 * 'struct sock_common', hence make an exception for it. This
 		 * allows bpf_sk_release to work for multiple socket types.
@@ -5973,6 +5985,7 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env,
 	 * fixed offset.
 	 */
 	case PTR_TO_BTF_ID:
+	case PTR_TO_BTF_ID | PTR_TRUSTED:
 		/* When referenced PTR_TO_BTF_ID is passed to release function,
 		 * it's fixed offset must be 0.	In the other cases, fixed offset
 		 * can be non-zero.
@@ -13690,6 +13703,8 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 			break;
 		case PTR_TO_BTF_ID:
 		case PTR_TO_BTF_ID | PTR_UNTRUSTED:
+		case PTR_TO_BTF_ID | PTR_TRUSTED:
+		case PTR_TO_BTF_ID | PTR_UNTRUSTED | PTR_TRUSTED:
 			if (type == BPF_READ) {
 				insn->code = BPF_LDX | BPF_PROBE_MEM |
 					BPF_SIZE((insn)->code);
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f2d8d070d024..5b9008bc597b 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -774,7 +774,7 @@ BPF_CALL_0(bpf_get_current_task_btf)
 const struct bpf_func_proto bpf_get_current_task_btf_proto = {
 	.func		= bpf_get_current_task_btf,
 	.gpl_only	= true,
-	.ret_type	= RET_PTR_TO_BTF_ID,
+	.ret_type	= RET_PTR_TO_BTF_ID_TRUSTED,
 	.ret_btf_id	= &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
 };
 
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index d15c91de995f..0006b5438ff7 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -61,7 +61,9 @@ static bool bpf_tcp_ca_is_valid_access(int off, int size,
 	if (!bpf_tracing_btf_ctx_access(off, size, type, prog, info))
 		return false;
 
-	if (info->reg_type == PTR_TO_BTF_ID && info->btf_id == sock_id)
+	if (base_type(info->reg_type) == PTR_TO_BTF_ID &&
+	    !(type_flag(info->reg_type) & ~PTR_TRUSTED) &&
+	    info->btf_id == sock_id)
 		/* promote it to tcp_sock */
 		info->btf_id = tcp_sock_id;
 
diff --git a/tools/testing/selftests/bpf/verifier/calls.c b/tools/testing/selftests/bpf/verifier/calls.c
index e1a937277b54..7ac947f00df4 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 pointer type STRUCT prog_test_ref_kfunc must point",
+	.errstr = "arg#0 pointer had unexpected modifiers",
 	.fixup_kfunc_btf_id = {
 		{ "bpf_kfunc_call_test_acquire", 3 },
 		{ "bpf_kfunc_call_test_release", 5 },
diff --git a/tools/testing/selftests/bpf/verifier/ref_tracking.c b/tools/testing/selftests/bpf/verifier/ref_tracking.c
index fd683a32a276..d9367f2894b9 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 pointer type STRUCT bpf_key must point to scalar, or struct with scalar",
+	.errstr = "arg#0 pointer had unexpected modifiers",
 	.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 pointer type STRUCT bpf_key must point to scalar, or struct with scalar",
+	.errstr = "arg#0 pointer had unexpected modifiers",
 	.fixup_kfunc_btf_id = {
 		{ "bpf_lookup_system_key", 1 },
 		{ "bpf_key_put", 3 },
-- 
2.38.1