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-rw-r--r--include/linux/bpf.h4
-rw-r--r--include/linux/bpf_verifier.h1
-rw-r--r--kernel/bpf/btf.c29
-rw-r--r--kernel/bpf/verifier.c113
-rw-r--r--tools/testing/selftests/bpf/bpf_experimental.h31
5 files changed, 160 insertions, 18 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 16740ee82082..30063a760b5a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2422,9 +2422,11 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
int btf_check_subprog_call(struct bpf_verifier_env *env, int subprog,
struct bpf_reg_state *regs);
int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
- struct bpf_reg_state *reg);
+ struct bpf_reg_state *reg, bool is_ex_cb);
int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
struct btf *btf, const struct btf_type *t);
+const char *btf_find_decl_tag_value(const struct btf *btf, const struct btf_type *pt,
+ int comp_idx, const char *tag_key);
struct bpf_prog *bpf_prog_by_id(u32 id);
struct bpf_link *bpf_link_by_id(u32 id);
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index da21a3ec5027..94ec766432f5 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -300,6 +300,7 @@ struct bpf_func_state {
bool in_callback_fn;
struct tnum callback_ret_range;
bool in_async_callback_fn;
+ bool in_exception_callback_fn;
/* The following fields should be last. See copy_func_state() */
int acquired_refs;
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 187b57276fec..f93e835d90af 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3310,10 +3310,10 @@ static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
return BTF_FIELD_FOUND;
}
-static const char *btf_find_decl_tag_value(const struct btf *btf,
- const struct btf_type *pt,
- int comp_idx, const char *tag_key)
+const char *btf_find_decl_tag_value(const struct btf *btf, const struct btf_type *pt,
+ int comp_idx, const char *tag_key)
{
+ const char *value = NULL;
int i;
for (i = 1; i < btf_nr_types(btf); i++) {
@@ -3327,9 +3327,14 @@ static const char *btf_find_decl_tag_value(const struct btf *btf,
continue;
if (strncmp(__btf_name_by_offset(btf, t->name_off), tag_key, len))
continue;
- return __btf_name_by_offset(btf, t->name_off) + len;
+ /* Prevent duplicate entries for same type */
+ if (value)
+ return ERR_PTR(-EEXIST);
+ value = __btf_name_by_offset(btf, t->name_off) + len;
}
- return NULL;
+ if (!value)
+ return ERR_PTR(-ENOENT);
+ return value;
}
static int
@@ -3347,7 +3352,7 @@ btf_find_graph_root(const struct btf *btf, const struct btf_type *pt,
if (t->size != sz)
return BTF_FIELD_IGNORE;
value_type = btf_find_decl_tag_value(btf, pt, comp_idx, "contains:");
- if (!value_type)
+ if (IS_ERR(value_type))
return -EINVAL;
node_field_name = strstr(value_type, ":");
if (!node_field_name)
@@ -6954,7 +6959,7 @@ int btf_check_subprog_call(struct bpf_verifier_env *env, int subprog,
* (either PTR_TO_CTX or SCALAR_VALUE).
*/
int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
- struct bpf_reg_state *regs)
+ struct bpf_reg_state *regs, bool is_ex_cb)
{
struct bpf_verifier_log *log = &env->log;
struct bpf_prog *prog = env->prog;
@@ -7011,7 +7016,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
tname, nargs, MAX_BPF_FUNC_REG_ARGS);
return -EINVAL;
}
- /* check that function returns int */
+ /* check that function returns int, exception cb also requires this */
t = btf_type_by_id(btf, t->type);
while (btf_type_is_modifier(t))
t = btf_type_by_id(btf, t->type);
@@ -7060,6 +7065,14 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
i, btf_type_str(t), tname);
return -EINVAL;
}
+ /* We have already ensured that the callback returns an integer, just
+ * like all global subprogs. We need to determine it only has a single
+ * scalar argument.
+ */
+ if (is_ex_cb && (nargs != 1 || regs[BPF_REG_1].type != SCALAR_VALUE)) {
+ bpf_log(log, "exception cb only supports single integer argument\n");
+ return -EINVAL;
+ }
return 0;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ec767ae08c2b..ec3f22312516 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2457,6 +2457,68 @@ static int add_subprog(struct bpf_verifier_env *env, int off)
return env->subprog_cnt - 1;
}
+static int bpf_find_exception_callback_insn_off(struct bpf_verifier_env *env)
+{
+ struct bpf_prog_aux *aux = env->prog->aux;
+ struct btf *btf = aux->btf;
+ const struct btf_type *t;
+ u32 main_btf_id, id;
+ const char *name;
+ int ret, i;
+
+ /* Non-zero func_info_cnt implies valid btf */
+ if (!aux->func_info_cnt)
+ return 0;
+ main_btf_id = aux->func_info[0].type_id;
+
+ t = btf_type_by_id(btf, main_btf_id);
+ if (!t) {
+ verbose(env, "invalid btf id for main subprog in func_info\n");
+ return -EINVAL;
+ }
+
+ name = btf_find_decl_tag_value(btf, t, -1, "exception_callback:");
+ if (IS_ERR(name)) {
+ ret = PTR_ERR(name);
+ /* If there is no tag present, there is no exception callback */
+ if (ret == -ENOENT)
+ ret = 0;
+ else if (ret == -EEXIST)
+ verbose(env, "multiple exception callback tags for main subprog\n");
+ return ret;
+ }
+
+ ret = btf_find_by_name_kind(btf, name, BTF_KIND_FUNC);
+ if (ret < 0) {
+ verbose(env, "exception callback '%s' could not be found in BTF\n", name);
+ return ret;
+ }
+ id = ret;
+ t = btf_type_by_id(btf, id);
+ if (btf_func_linkage(t) != BTF_FUNC_GLOBAL) {
+ verbose(env, "exception callback '%s' must have global linkage\n", name);
+ return -EINVAL;
+ }
+ ret = 0;
+ for (i = 0; i < aux->func_info_cnt; i++) {
+ if (aux->func_info[i].type_id != id)
+ continue;
+ ret = aux->func_info[i].insn_off;
+ /* Further func_info and subprog checks will also happen
+ * later, so assume this is the right insn_off for now.
+ */
+ if (!ret) {
+ verbose(env, "invalid exception callback insn_off in func_info: 0\n");
+ ret = -EINVAL;
+ }
+ }
+ if (!ret) {
+ verbose(env, "exception callback type id not found in func_info\n");
+ ret = -EINVAL;
+ }
+ return ret;
+}
+
#define MAX_KFUNC_DESCS 256
#define MAX_KFUNC_BTFS 256
@@ -2796,8 +2858,8 @@ bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
{
struct bpf_subprog_info *subprog = env->subprog_info;
+ int i, ret, insn_cnt = env->prog->len, ex_cb_insn;
struct bpf_insn *insn = env->prog->insnsi;
- int i, ret, insn_cnt = env->prog->len;
/* Add entry function. */
ret = add_subprog(env, 0);
@@ -2823,6 +2885,26 @@ static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
return ret;
}
+ ret = bpf_find_exception_callback_insn_off(env);
+ if (ret < 0)
+ return ret;
+ ex_cb_insn = ret;
+
+ /* If ex_cb_insn > 0, this means that the main program has a subprog
+ * marked using BTF decl tag to serve as the exception callback.
+ */
+ if (ex_cb_insn) {
+ ret = add_subprog(env, ex_cb_insn);
+ if (ret < 0)
+ return ret;
+ for (i = 1; i < env->subprog_cnt; i++) {
+ if (env->subprog_info[i].start != ex_cb_insn)
+ continue;
+ env->exception_callback_subprog = i;
+ break;
+ }
+ }
+
/* Add a fake 'exit' subprog which could simplify subprog iteration
* logic. 'subprog_cnt' should not be increased.
*/
@@ -5707,6 +5789,10 @@ continue_func:
/* async callbacks don't increase bpf prog stack size unless called directly */
if (!bpf_pseudo_call(insn + i))
continue;
+ if (subprog[sidx].is_exception_cb) {
+ verbose(env, "insn %d cannot call exception cb directly\n", i);
+ return -EINVAL;
+ }
}
i = next_insn;
idx = sidx;
@@ -5728,8 +5814,13 @@ continue_func:
* tail call counter throughout bpf2bpf calls combined with tailcalls
*/
if (tail_call_reachable)
- for (j = 0; j < frame; j++)
+ for (j = 0; j < frame; j++) {
+ if (subprog[ret_prog[j]].is_exception_cb) {
+ verbose(env, "cannot tail call within exception cb\n");
+ return -EINVAL;
+ }
subprog[ret_prog[j]].tail_call_reachable = true;
+ }
if (subprog[0].tail_call_reachable)
env->prog->aux->tail_call_reachable = true;
@@ -14630,7 +14721,7 @@ static int check_return_code(struct bpf_verifier_env *env)
const bool is_subprog = frame->subprogno;
/* LSM and struct_ops func-ptr's return type could be "void" */
- if (!is_subprog) {
+ if (!is_subprog || frame->in_exception_callback_fn) {
switch (prog_type) {
case BPF_PROG_TYPE_LSM:
if (prog->expected_attach_type == BPF_LSM_CGROUP)
@@ -14678,7 +14769,7 @@ static int check_return_code(struct bpf_verifier_env *env)
return 0;
}
- if (is_subprog) {
+ if (is_subprog && !frame->in_exception_callback_fn) {
if (reg->type != SCALAR_VALUE) {
verbose(env, "At subprogram exit the register R0 is not a scalar value (%s)\n",
reg_type_str(env, reg->type));
@@ -19334,7 +19425,7 @@ static void free_states(struct bpf_verifier_env *env)
}
}
-static int do_check_common(struct bpf_verifier_env *env, int subprog)
+static int do_check_common(struct bpf_verifier_env *env, int subprog, bool is_ex_cb)
{
bool pop_log = !(env->log.level & BPF_LOG_LEVEL2);
struct bpf_verifier_state *state;
@@ -19365,7 +19456,7 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
regs = state->frame[state->curframe]->regs;
if (subprog || env->prog->type == BPF_PROG_TYPE_EXT) {
- ret = btf_prepare_func_args(env, subprog, regs);
+ ret = btf_prepare_func_args(env, subprog, regs, is_ex_cb);
if (ret)
goto out;
for (i = BPF_REG_1; i <= BPF_REG_5; i++) {
@@ -19381,6 +19472,12 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
regs[i].id = ++env->id_gen;
}
}
+ if (is_ex_cb) {
+ state->frame[0]->in_exception_callback_fn = true;
+ env->subprog_info[subprog].is_cb = true;
+ env->subprog_info[subprog].is_async_cb = true;
+ env->subprog_info[subprog].is_exception_cb = true;
+ }
} else {
/* 1st arg to a function */
regs[BPF_REG_1].type = PTR_TO_CTX;
@@ -19445,7 +19542,7 @@ static int do_check_subprogs(struct bpf_verifier_env *env)
continue;
env->insn_idx = env->subprog_info[i].start;
WARN_ON_ONCE(env->insn_idx == 0);
- ret = do_check_common(env, i);
+ ret = do_check_common(env, i, env->exception_callback_subprog == i);
if (ret) {
return ret;
} else if (env->log.level & BPF_LOG_LEVEL) {
@@ -19462,7 +19559,7 @@ static int do_check_main(struct bpf_verifier_env *env)
int ret;
env->insn_idx = 0;
- ret = do_check_common(env, 0);
+ ret = do_check_common(env, 0, false);
if (!ret)
env->prog->aux->stack_depth = env->subprog_info[0].stack_depth;
return ret;
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 333b54a86e3a..9a87170524ce 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -165,7 +165,16 @@ extern void bpf_percpu_obj_drop_impl(void *kptr, void *meta) __ksym;
/* Description
* Throw a BPF exception from the program, immediately terminating its
* execution and unwinding the stack. The supplied 'cookie' parameter
- * will be the return value of the program when an exception is thrown.
+ * will be the return value of the program when an exception is thrown,
+ * and the default exception callback is used. Otherwise, if an exception
+ * callback is set using the '__exception_cb(callback)' declaration tag
+ * on the main program, the 'cookie' parameter will be the callback's only
+ * input argument.
+ *
+ * Thus, in case of default exception callback, 'cookie' is subjected to
+ * constraints on the program's return value (as with R0 on exit).
+ * Otherwise, the return value of the marked exception callback will be
+ * subjected to the same checks.
*
* Note that throwing an exception with lingering resources (locks,
* references, etc.) will lead to a verification error.
@@ -178,4 +187,24 @@ extern void bpf_percpu_obj_drop_impl(void *kptr, void *meta) __ksym;
*/
extern void bpf_throw(u64 cookie) __ksym;
+/* This macro must be used to mark the exception callback corresponding to the
+ * main program. For example:
+ *
+ * int exception_cb(u64 cookie) {
+ * return cookie;
+ * }
+ *
+ * SEC("tc")
+ * __exception_cb(exception_cb)
+ * int main_prog(struct __sk_buff *ctx) {
+ * ...
+ * return TC_ACT_OK;
+ * }
+ *
+ * Here, exception callback for the main program will be 'exception_cb'. Note
+ * that this attribute can only be used once, and multiple exception callbacks
+ * specified for the main program will lead to verification error.
+ */
+#define __exception_cb(name) __attribute__((btf_decl_tag("exception_callback:" #name)))
+
#endif
generated by cgit (git 2.34.1) at 2024-06-15 14:08:37 +0000