diff mbox series

[bpf-next,v8,03/11] bpf: verifier: refactor check_attach_btf_id()

Message ID 160079991702.8301.18141427563623823055.stgit@toke.dk
State Changes Requested
Delegated to: BPF Maintainers
Headers show
Series bpf: Support multi-attach for freplace programs | expand

Commit Message

Toke Høiland-Jørgensen Sept. 22, 2020, 6:38 p.m. UTC 
From: Toke Høiland-Jørgensen <toke@redhat.com>

The check_attach_btf_id() function really does three things:

1. It performs a bunch of checks on the program to ensure that the
   attachment is valid.

2. It stores a bunch of state about the attachment being requested in
   the verifier environment and struct bpf_prog objects.

3. It allocates a trampoline for the attachment.

This patch splits out (1.) and (3.) into separate functions in preparation
for reusing them when the actual attachment is happening (in the
raw_tracepoint_open syscall operation), which will allow tracing programs
to have multiple (compatible) attachments.

This also fixes a bug where a bunch of checks were skipped if a trampoline
already existed for the tracing target.

Fixes: 6ba43b761c41 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
Fixes: 1e6c62a88215 ("bpf: Introduce sleepable BPF programs")
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 include/linux/bpf.h          |    7 +
 include/linux/bpf_verifier.h |    9 ++
 kernel/bpf/trampoline.c      |   20 ++++
 kernel/bpf/verifier.c        |  200 ++++++++++++++++++++++++------------------
 4 files changed, 150 insertions(+), 86 deletions(-)

Comments

Alexei Starovoitov Sept. 23, 2020, 11:54 p.m. UTC | #1 
On Tue, Sep 22, 2020 at 08:38:37PM +0200, Toke Høiland-Jørgensen wrote:
> From: Toke Høiland-Jørgensen <toke@redhat.com>
> 
> The check_attach_btf_id() function really does three things:
> 
> 1. It performs a bunch of checks on the program to ensure that the
>    attachment is valid.
> 
> 2. It stores a bunch of state about the attachment being requested in
>    the verifier environment and struct bpf_prog objects.
> 
> 3. It allocates a trampoline for the attachment.
> 
> This patch splits out (1.) and (3.) into separate functions in preparation
> for reusing them when the actual attachment is happening (in the
> raw_tracepoint_open syscall operation), which will allow tracing programs
> to have multiple (compatible) attachments.

raw_tp_open part is no longer correct.

Also could you re-phrase it that 'stores a bunch of state about the attechment'
is still the case. It doesn't store into bpf_prog directly, but returns instead.

> This also fixes a bug where a bunch of checks were skipped if a trampoline
> already existed for the tracing target.

This time we were lucky. When you see such selftests failures please debug
them before submitting the patches. The reviewers should not be pointing out
that the patch broke some tests.
If anything breaks please mention it in the cover letter.

> -static int check_attach_modify_return(struct bpf_prog *prog, unsigned long addr)
> +static int check_attach_modify_return(const struct bpf_prog *prog, unsigned long addr,
> +				      const char *func_name)

Since you're adding 'func_name' why keep 'prog' there? Pls drop it.

>  {
>  	if (within_error_injection_list(addr) ||
> -	    !strncmp(SECURITY_PREFIX, prog->aux->attach_func_name,
> -		     sizeof(SECURITY_PREFIX) - 1))
> +	    !strncmp(SECURITY_PREFIX, func_name, sizeof(SECURITY_PREFIX) - 1))
>  		return 0;
>  
>  	return -EINVAL;
> @@ -11215,43 +11215,29 @@ static int check_non_sleepable_error_inject(u32 btf_id)
>  	return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id);
>  }
>  
> -static int check_attach_btf_id(struct bpf_verifier_env *env)
> +int bpf_check_attach_target(struct bpf_verifier_log *log,
> +			    const struct bpf_prog *prog,
> +			    const struct bpf_prog *tgt_prog,
> +			    u32 btf_id,
> +			    struct btf_func_model *fmodel,
> +			    long *tgt_addr,
> +			    const char **tgt_name,
> +			    const struct btf_type **tgt_type)

How about grouping the return args into
struct bpf_attach_target_info {
 struct btf_func_model fmodel;
 long tgt_addr;
 const char *tgt_name;
 const struct btf_type *tgt_type;
};
allocate it on stack in the caller and pass a pointer into this function?

The same way pass the whole &bpf_attach_target_info into bpf_trampoline_get().
It will use fmodel and tgt_addr out of it, but it doesn't hurt to pass
the whole thing.

Overall I like the refactoring, but this prototype and conditional
if (tgt_name) *tgt_name =; and if (tgt_type) makes it harder to comprehend.

>  		if (!tgt_prog->jited) {
>  			bpf_log(log, "Can attach to only JITed progs\n");
> @@ -11328,13 +11312,11 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
>  			bpf_log(log, "Cannot extend fentry/fexit\n");
>  			return -EINVAL;
>  		}
> -		key = ((u64)aux->id) << 32 | btf_id;

Could you please refactor key computation into a helper as well?
Especially since it will be used out of verifier.c and from syscall.c.
Something like this for bpf.h
static inline u64 bpf_trampoline_compute_key(struct bpf_prog *tgt_prog, u32 btf_id)
{
        if (tgt_prog) {
                return ((u64)tgt_prog->aux->id) << 32 | btf_id;
        } else {
                return btf_id;
        }
}

> +	ret = bpf_check_attach_target(&env->log, prog, tgt_prog, btf_id,
> +				      &fmodel, &addr, &tname, &t);
> +	if (ret)
>  		return ret;
> +
> +	if (tgt_prog) {
> +		if (prog->type == BPF_PROG_TYPE_EXT) {
> +			env->ops = bpf_verifier_ops[tgt_prog->type];
> +			prog->expected_attach_type =
> +				tgt_prog->expected_attach_type;
> +		}
> +		key = ((u64)tgt_prog->aux->id) << 32 | btf_id;
> +	} else {
> +		key = btf_id;
>  	}

and here it would be:
if (tgt_prog && prog->type == BPF_PROG_TYPE_EXT) {
	env->ops = bpf_verifier_ops[tgt_prog->type];
	prog->expected_attach_type = tgt_prog->expected_attach_type;
}
key = bpf_trampoline_compute_key(tgt_prog, btf_id);

otherwise above 'if' groups two separate things.
It's not pretty in the existing code, no doubt, but since you're doing
nice cleanup let's make it clean here too.

> +
> +	/* remember two read only pointers that are valid for
> +	 * the life time of the kernel
> +	 */

Here this comment is not correct.
It was correct in the place you copy-pasted it from, but not here.
Please think it through and adjust accordingly.
diff mbox series

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 1f9e7c22cc7e..a1760fd87815 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -621,6 +621,8 @@  static __always_inline unsigned int bpf_dispatcher_nop_func(
 struct bpf_trampoline *bpf_trampoline_lookup(u64 key);
 int bpf_trampoline_link_prog(struct bpf_prog *prog);
 int bpf_trampoline_unlink_prog(struct bpf_prog *prog);
+struct bpf_trampoline *bpf_trampoline_get(u64 key, void *addr,
+					  struct btf_func_model *fmodel);
 void bpf_trampoline_put(struct bpf_trampoline *tr);
 #define BPF_DISPATCHER_INIT(_name) {				\
 	.mutex = __MUTEX_INITIALIZER(_name.mutex),		\
@@ -677,6 +679,11 @@  static inline int bpf_trampoline_unlink_prog(struct bpf_prog *prog)
 {
 	return -ENOTSUPP;
 }
+static inline struct bpf_trampoline *bpf_trampoline_get(u64 key, void *addr,
+							struct btf_func_model *fmodel)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
 static inline void bpf_trampoline_put(struct bpf_trampoline *tr) {}
 #define DEFINE_BPF_DISPATCHER(name)
 #define DECLARE_BPF_DISPATCHER(name)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7bc9276c4ef4..4fe718a5b4cd 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -450,4 +450,13 @@  bpf_prog_offload_remove_insns(struct bpf_verifier_env *env, u32 off, u32 cnt);
 int check_ctx_reg(struct bpf_verifier_env *env,
 		  const struct bpf_reg_state *reg, int regno);
 
+int bpf_check_attach_target(struct bpf_verifier_log *log,
+			    const struct bpf_prog *prog,
+			    const struct bpf_prog *tgt_prog,
+			    u32 btf_id,
+			    struct btf_func_model *fmodel,
+			    long *tgt_addr,
+			    const char **tgt_name,
+			    const struct btf_type **tgt_type);
+
 #endif /* _LINUX_BPF_VERIFIER_H */
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 7dd523a7e32d..e86d32f7f7dc 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -336,6 +336,26 @@  int bpf_trampoline_unlink_prog(struct bpf_prog *prog)
 	return err;
 }
 
+struct bpf_trampoline *bpf_trampoline_get(u64 key, void *addr,
+					  struct btf_func_model *fmodel)
+{
+	struct bpf_trampoline *tr;
+
+	tr = bpf_trampoline_lookup(key);
+	if (!tr)
+		return NULL;
+
+	mutex_lock(&tr->mutex);
+	if (tr->func.addr)
+		goto out;
+
+	memcpy(&tr->func.model, fmodel, sizeof(*fmodel));
+	tr->func.addr = addr;
+out:
+	mutex_unlock(&tr->mutex);
+	return tr;
+}
+
 void bpf_trampoline_put(struct bpf_trampoline *tr)
 {
 	if (!tr)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 81e1bdc492f8..ad244a606d7a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11174,11 +11174,11 @@  static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 }
 #define SECURITY_PREFIX "security_"
 
-static int check_attach_modify_return(struct bpf_prog *prog, unsigned long addr)
+static int check_attach_modify_return(const struct bpf_prog *prog, unsigned long addr,
+				      const char *func_name)
 {
 	if (within_error_injection_list(addr) ||
-	    !strncmp(SECURITY_PREFIX, prog->aux->attach_func_name,
-		     sizeof(SECURITY_PREFIX) - 1))
+	    !strncmp(SECURITY_PREFIX, func_name, sizeof(SECURITY_PREFIX) - 1))
 		return 0;
 
 	return -EINVAL;
@@ -11215,43 +11215,29 @@  static int check_non_sleepable_error_inject(u32 btf_id)
 	return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id);
 }
 
-static int check_attach_btf_id(struct bpf_verifier_env *env)
+int bpf_check_attach_target(struct bpf_verifier_log *log,
+			    const struct bpf_prog *prog,
+			    const struct bpf_prog *tgt_prog,
+			    u32 btf_id,
+			    struct btf_func_model *fmodel,
+			    long *tgt_addr,
+			    const char **tgt_name,
+			    const struct btf_type **tgt_type)
 {
-	struct bpf_prog *prog = env->prog;
 	bool prog_extension = prog->type == BPF_PROG_TYPE_EXT;
-	struct bpf_prog *tgt_prog = prog->aux->linked_prog;
-	struct bpf_verifier_log *log = &env->log;
-	u32 btf_id = prog->aux->attach_btf_id;
 	const char prefix[] = "btf_trace_";
-	struct btf_func_model fmodel;
 	int ret = 0, subprog = -1, i;
-	struct bpf_trampoline *tr;
 	const struct btf_type *t;
 	bool conservative = true;
 	const char *tname;
 	struct btf *btf;
-	long addr;
-	u64 key;
-
-	if (prog->aux->sleepable && prog->type != BPF_PROG_TYPE_TRACING &&
-	    prog->type != BPF_PROG_TYPE_LSM) {
-		verbose(env, "Only fentry/fexit/fmod_ret and lsm programs can be sleepable\n");
-		return -EINVAL;
-	}
-
-	if (prog->type == BPF_PROG_TYPE_STRUCT_OPS)
-		return check_struct_ops_btf_id(env);
-
-	if (prog->type != BPF_PROG_TYPE_TRACING &&
-	    prog->type != BPF_PROG_TYPE_LSM &&
-	    !prog_extension)
-		return 0;
+	long addr = 0;
 
 	if (!btf_id) {
 		bpf_log(log, "Tracing programs must provide btf_id\n");
 		return -EINVAL;
 	}
-	btf = bpf_prog_get_target_btf(prog);
+	btf = tgt_prog ? tgt_prog->aux->btf : btf_vmlinux;
 	if (!btf) {
 		bpf_log(log,
 			"FENTRY/FEXIT program can only be attached to another program annotated with BTF\n");
@@ -11291,8 +11277,6 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 					"Extension programs should be JITed\n");
 				return -EINVAL;
 			}
-			env->ops = bpf_verifier_ops[tgt_prog->type];
-			prog->expected_attach_type = tgt_prog->expected_attach_type;
 		}
 		if (!tgt_prog->jited) {
 			bpf_log(log, "Can attach to only JITed progs\n");
@@ -11328,13 +11312,11 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 			bpf_log(log, "Cannot extend fentry/fexit\n");
 			return -EINVAL;
 		}
-		key = ((u64)aux->id) << 32 | btf_id;
 	} else {
 		if (prog_extension) {
 			bpf_log(log, "Cannot replace kernel functions\n");
 			return -EINVAL;
 		}
-		key = btf_id;
 	}
 
 	switch (prog->expected_attach_type) {
@@ -11364,13 +11346,7 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 			/* should never happen in valid vmlinux build */
 			return -EINVAL;
 
-		/* remember two read only pointers that are valid for
-		 * the life time of the kernel
-		 */
-		prog->aux->attach_func_name = tname;
-		prog->aux->attach_func_proto = t;
-		prog->aux->attach_btf_trace = true;
-		return 0;
+		break;
 	case BPF_TRACE_ITER:
 		if (!btf_type_is_func(t)) {
 			bpf_log(log, "attach_btf_id %u is not a function\n",
@@ -11380,12 +11356,10 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 		t = btf_type_by_id(btf, t->type);
 		if (!btf_type_is_func_proto(t))
 			return -EINVAL;
-		prog->aux->attach_func_name = tname;
-		prog->aux->attach_func_proto = t;
-		if (!bpf_iter_prog_supported(prog))
-			return -EINVAL;
-		ret = btf_distill_func_proto(log, btf, t, tname, &fmodel);
-		return ret;
+		ret = btf_distill_func_proto(log, btf, t, tname, fmodel);
+		if (ret)
+			return ret;
+		break;
 	default:
 		if (!prog_extension)
 			return -EINVAL;
@@ -11394,13 +11368,6 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 	case BPF_LSM_MAC:
 	case BPF_TRACE_FENTRY:
 	case BPF_TRACE_FEXIT:
-		prog->aux->attach_func_name = tname;
-		if (prog->type == BPF_PROG_TYPE_LSM) {
-			ret = bpf_lsm_verify_prog(log, prog);
-			if (ret < 0)
-				return ret;
-		}
-
 		if (!btf_type_is_func(t)) {
 			bpf_log(log, "attach_btf_id %u is not a function\n",
 				btf_id);
@@ -11412,24 +11379,14 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 		t = btf_type_by_id(btf, t->type);
 		if (!btf_type_is_func_proto(t))
 			return -EINVAL;
-		tr = bpf_trampoline_lookup(key);
-		if (!tr)
-			return -ENOMEM;
-		/* t is either vmlinux type or another program's type */
-		prog->aux->attach_func_proto = t;
-		mutex_lock(&tr->mutex);
-		if (tr->func.addr) {
-			prog->aux->trampoline = tr;
-			goto out;
-		}
-		if (tgt_prog && conservative) {
-			prog->aux->attach_func_proto = NULL;
+
+		if (tgt_prog && conservative)
 			t = NULL;
-		}
-		ret = btf_distill_func_proto(log, btf, t,
-					     tname, &tr->func.model);
+
+		ret = btf_distill_func_proto(log, btf, t, tname, fmodel);
 		if (ret < 0)
-			goto out;
+			return ret;
+
 		if (tgt_prog) {
 			if (subprog == 0)
 				addr = (long) tgt_prog->bpf_func;
@@ -11441,8 +11398,7 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 				bpf_log(log,
 					"The address of function %s cannot be found\n",
 					tname);
-				ret = -ENOENT;
-				goto out;
+				return -ENOENT;
 			}
 		}
 
@@ -11467,30 +11423,102 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 			default:
 				break;
 			}
-			if (ret)
-				bpf_log(log, "%s is not sleepable\n",
-					prog->aux->attach_func_name);
+			if (ret) {
+				bpf_log(log, "%s is not sleepable\n", tname);
+				return ret;
+			}
 		} else if (prog->expected_attach_type == BPF_MODIFY_RETURN) {
 			if (tgt_prog) {
 				bpf_log(log, "can't modify return codes of BPF programs\n");
-				ret = -EINVAL;
-				goto out;
+				return -EINVAL;
+			}
+			ret = check_attach_modify_return(prog, addr, tname);
+			if (ret) {
+				bpf_log(log, "%s() is not modifiable\n", tname);
+				return ret;
 			}
-			ret = check_attach_modify_return(prog, addr);
-			if (ret)
-				bpf_log(log, "%s() is not modifiable\n",
-					prog->aux->attach_func_name);
 		}
-		if (ret)
-			goto out;
-		tr->func.addr = (void *)addr;
-		prog->aux->trampoline = tr;
-out:
-		mutex_unlock(&tr->mutex);
-		if (ret)
-			bpf_trampoline_put(tr);
+
+		break;
+	}
+	*tgt_addr = addr;
+	if (tgt_name)
+		*tgt_name = tname;
+	if (tgt_type)
+		*tgt_type = t;
+	return 0;
+}
+
+static int check_attach_btf_id(struct bpf_verifier_env *env)
+{
+	struct bpf_prog *prog = env->prog;
+	struct bpf_prog *tgt_prog = prog->aux->linked_prog;
+	u32 btf_id = prog->aux->attach_btf_id;
+	struct btf_func_model fmodel;
+	struct bpf_trampoline *tr;
+	const struct btf_type *t;
+	const char *tname;
+	long addr;
+	int ret;
+	u64 key;
+
+	if (prog->aux->sleepable && prog->type != BPF_PROG_TYPE_TRACING &&
+	    prog->type != BPF_PROG_TYPE_LSM) {
+		verbose(env, "Only fentry/fexit/fmod_ret and lsm programs can be sleepable\n");
+		return -EINVAL;
+	}
+
+	if (prog->type == BPF_PROG_TYPE_STRUCT_OPS)
+		return check_struct_ops_btf_id(env);
+
+	if (prog->type != BPF_PROG_TYPE_TRACING &&
+	    prog->type != BPF_PROG_TYPE_LSM &&
+	    prog->type != BPF_PROG_TYPE_EXT)
+		return 0;
+
+	ret = bpf_check_attach_target(&env->log, prog, tgt_prog, btf_id,
+				      &fmodel, &addr, &tname, &t);
+	if (ret)
 		return ret;
+
+	if (tgt_prog) {
+		if (prog->type == BPF_PROG_TYPE_EXT) {
+			env->ops = bpf_verifier_ops[tgt_prog->type];
+			prog->expected_attach_type =
+				tgt_prog->expected_attach_type;
+		}
+		key = ((u64)tgt_prog->aux->id) << 32 | btf_id;
+	} else {
+		key = btf_id;
 	}
+
+	/* remember two read only pointers that are valid for
+	 * the life time of the kernel
+	 */
+	prog->aux->attach_func_proto = t;
+	prog->aux->attach_func_name = tname;
+
+	if (prog->expected_attach_type == BPF_TRACE_RAW_TP) {
+		prog->aux->attach_btf_trace = true;
+		return 0;
+	} else if (prog->expected_attach_type == BPF_TRACE_ITER) {
+		if (!bpf_iter_prog_supported(prog))
+			return -EINVAL;
+		return 0;
+	}
+
+	if (prog->type == BPF_PROG_TYPE_LSM) {
+		ret = bpf_lsm_verify_prog(&env->log, prog);
+		if (ret < 0)
+			return ret;
+	}
+
+	tr = bpf_trampoline_get(key, (void *)addr, &fmodel);
+	if (!tr)
+		return -ENOMEM;
+
+	prog->aux->trampoline = tr;
+	return 0;
 }
 
 int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,