From: "Emil Tsalapatis" <emil@etsalapatis.com>
To: "Emil Tsalapatis" <emil@etsalapatis.com>, <bpf@vger.kernel.org>
Cc: <andrii@kernel.org>, <ast@kernel.org>, <daniel@iogearbox.net>,
<eddyz87@gmail.com>, <martin.lau@kernel.org>, <memxor@gmail.com>,
<song@kernel.org>, <yonghong.song@linux.dev>
Subject: Re: [PATCH bpf-next v5 1/5] bpf: Factor out program return value calculation
Date: Fri, 27 Feb 2026 10:50:40 -0500 [thread overview]
Message-ID: <DGPV3UPSTRSK.1QB5KADDS30GS@etsalapatis.com> (raw)
In-Reply-To: <20260227154616.6846-2-emil@etsalapatis.com>
On Fri Feb 27, 2026 at 10:46 AM EST, Emil Tsalapatis wrote:
> Factor the return value range calculation logic in check_return_code
> out of the function in preparation for separating the return value
> validation logic for BPF_EXIT and bpf_throw().
>
> Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
> ---
> include/linux/bpf_verifier.h | 1 +
> kernel/bpf/verifier.c | 225 +++++++++++++++++++----------------
> 2 files changed, 126 insertions(+), 100 deletions(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index ef8e45a362d9..0e639613d8cf 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -266,6 +266,7 @@ struct bpf_reference_state {
> struct bpf_retval_range {
> s32 minval;
> s32 maxval;
> + bool return_32bit;
> };
>
> /* state of the program:
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index edf5342b982f..6cf2270c343c 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2925,7 +2925,11 @@ static void init_reg_state(struct bpf_verifier_env *env,
>
> static struct bpf_retval_range retval_range(s32 minval, s32 maxval)
> {
> - return (struct bpf_retval_range){ minval, maxval };
> + /*
> + * return_32bit is set to false by default and set explicitly
> + * by the caller when necessary.
> + */
> + return (struct bpf_retval_range){ minval, maxval, false };
> }
>
> #define BPF_MAIN_FUNC (-1)
> @@ -11146,10 +11150,9 @@ static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env)
> return is_rbtree_lock_required_kfunc(kfunc_btf_id);
> }
>
> -static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg,
> - bool return_32bit)
> +static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)
> {
> - if (return_32bit)
> + if (range.return_32bit)
> return range.minval <= reg->s32_min_value && reg->s32_max_value <= range.maxval;
> else
> return range.minval <= reg->smin_value && reg->smax_value <= range.maxval;
> @@ -11193,7 +11196,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
> return err;
>
> /* enforce R0 return value range, and bpf_callback_t returns 64bit */
> - if (!retval_range_within(callee->callback_ret_range, r0, false)) {
> + if (!retval_range_within(callee->callback_ret_range, r0)) {
> verbose_invalid_scalar(env, r0, callee->callback_ret_range,
> "At callback return", "R0");
> return -EINVAL;
> @@ -17837,6 +17840,115 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
> return 0;
> }
>
> +
> +static bool return_retval_range(struct bpf_verifier_env *env, struct bpf_retval_range *range)
> +{
> + enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
> +
> + /* Default return value range. */
> + *range = retval_range(0, 1);
> +
> + switch (prog_type) {
> + case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
> + switch (env->prog->expected_attach_type) {
> + case BPF_CGROUP_UDP4_RECVMSG:
> + case BPF_CGROUP_UDP6_RECVMSG:
> + case BPF_CGROUP_UNIX_RECVMSG:
> + case BPF_CGROUP_INET4_GETPEERNAME:
> + case BPF_CGROUP_INET6_GETPEERNAME:
> + case BPF_CGROUP_UNIX_GETPEERNAME:
> + case BPF_CGROUP_INET4_GETSOCKNAME:
> + case BPF_CGROUP_INET6_GETSOCKNAME:
> + case BPF_CGROUP_UNIX_GETSOCKNAME:
> + *range = retval_range(1, 1);
> + break;
> + case BPF_CGROUP_INET4_BIND:
> + case BPF_CGROUP_INET6_BIND:
> + *range = retval_range(0, 3);
> + break;
> + default:
> + break;
> + }
> + break;
> + case BPF_PROG_TYPE_CGROUP_SKB:
> + if (env->prog->expected_attach_type == BPF_CGROUP_INET_EGRESS)
> + *range = retval_range(0, 3);
> + break;
> + case BPF_PROG_TYPE_CGROUP_SOCK:
> + case BPF_PROG_TYPE_SOCK_OPS:
> + case BPF_PROG_TYPE_CGROUP_DEVICE:
> + case BPF_PROG_TYPE_CGROUP_SYSCTL:
> + case BPF_PROG_TYPE_CGROUP_SOCKOPT:
> + break;
> + case BPF_PROG_TYPE_RAW_TRACEPOINT:
> + if (!env->prog->aux->attach_btf_id)
> + return false;
> + *range = retval_range(0, 0);
> + break;
> + case BPF_PROG_TYPE_TRACING:
> + switch (env->prog->expected_attach_type) {
> + case BPF_TRACE_FENTRY:
> + case BPF_TRACE_FEXIT:
> + case BPF_TRACE_FSESSION:
> + *range = retval_range(0, 0);
> + break;
> + case BPF_TRACE_RAW_TP:
> + case BPF_MODIFY_RETURN:
> + return false;
> + case BPF_TRACE_ITER:
> + break;
> + default:
> + }
> + break;
> + case BPF_PROG_TYPE_KPROBE:
> + switch (env->prog->expected_attach_type) {
> + case BPF_TRACE_KPROBE_SESSION:
> + case BPF_TRACE_UPROBE_SESSION:
> + break;
> + default:
> + return false;
> + }
> + break;
> + case BPF_PROG_TYPE_SK_LOOKUP:
> + *range = retval_range(SK_DROP, SK_PASS);
> + break;
> +
> + case BPF_PROG_TYPE_LSM:
> + if (env->prog->expected_attach_type != BPF_LSM_CGROUP) {
> + /* no range found, any return value is allowed */
> + if (!get_func_retval_range(env->prog, range))
> + return false;
> + /* no restricted range, any return value is allowed */
> + if (range->minval == S32_MIN && range->maxval == S32_MAX)
> + return false;
> + range->return_32bit = true;
> + } else if (!env->prog->aux->attach_func_proto->type) {
> + /* Make sure programs that attach to void
> + * hooks don't try to modify return value.
> + */
> + *range = retval_range(1, 1);
> + }
> + break;
> +
> + case BPF_PROG_TYPE_NETFILTER:
> + *range = retval_range(NF_DROP, NF_ACCEPT);
> + break;
> + case BPF_PROG_TYPE_STRUCT_OPS:
> + *range = retval_range(0, 0);
> + break;
> + case BPF_PROG_TYPE_EXT:
> + /* freplace program can return anything as its return value
> + * depends on the to-be-replaced kernel func or bpf program.
> + */
> + default:
> + return false;
> + }
> +
> + /* Continue calculating. */
> +
> + return true;
> +}
> +
> static int check_return_code(struct bpf_verifier_env *env, int regno, const char *reg_name)
> {
> const char *exit_ctx = "At program exit";
> @@ -17845,7 +17957,7 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
> struct bpf_reg_state *reg = reg_state(env, regno);
> struct bpf_retval_range range = retval_range(0, 1);
> enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
> - int err;
> + int ret, err;
> struct bpf_func_state *frame = env->cur_state->frame[0];
> const bool is_subprog = frame->subprogno;
> bool return_32bit = false;
> @@ -17856,7 +17968,7 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
> switch (prog_type) {
> case BPF_PROG_TYPE_LSM:
> if (prog->expected_attach_type == BPF_LSM_CGROUP)
> - /* See below, can be 0 or 0-1 depending on hook. */
> + /* See return_retval_range, can be 0 or 0-1 depending on hook. */
> break;
> if (!prog->aux->attach_func_proto->type)
> return 0;
> @@ -17914,101 +18026,14 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
> return 0;
> }
>
> - switch (prog_type) {
> - case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
> - if (env->prog->expected_attach_type == BPF_CGROUP_UDP4_RECVMSG ||
> - env->prog->expected_attach_type == BPF_CGROUP_UDP6_RECVMSG ||
> - env->prog->expected_attach_type == BPF_CGROUP_UNIX_RECVMSG ||
> - env->prog->expected_attach_type == BPF_CGROUP_INET4_GETPEERNAME ||
> - env->prog->expected_attach_type == BPF_CGROUP_INET6_GETPEERNAME ||
> - env->prog->expected_attach_type == BPF_CGROUP_UNIX_GETPEERNAME ||
> - env->prog->expected_attach_type == BPF_CGROUP_INET4_GETSOCKNAME ||
> - env->prog->expected_attach_type == BPF_CGROUP_INET6_GETSOCKNAME ||
> - env->prog->expected_attach_type == BPF_CGROUP_UNIX_GETSOCKNAME)
> - range = retval_range(1, 1);
> - if (env->prog->expected_attach_type == BPF_CGROUP_INET4_BIND ||
> - env->prog->expected_attach_type == BPF_CGROUP_INET6_BIND)
> - range = retval_range(0, 3);
> - break;
> - case BPF_PROG_TYPE_CGROUP_SKB:
> - if (env->prog->expected_attach_type == BPF_CGROUP_INET_EGRESS) {
> - range = retval_range(0, 3);
> - enforce_attach_type_range = tnum_range(2, 3);
> - }
> - break;
> - case BPF_PROG_TYPE_CGROUP_SOCK:
> - case BPF_PROG_TYPE_SOCK_OPS:
> - case BPF_PROG_TYPE_CGROUP_DEVICE:
> - case BPF_PROG_TYPE_CGROUP_SYSCTL:
> - case BPF_PROG_TYPE_CGROUP_SOCKOPT:
> - break;
> - case BPF_PROG_TYPE_RAW_TRACEPOINT:
> - if (!env->prog->aux->attach_btf_id)
> - return 0;
> - range = retval_range(0, 0);
> - break;
> - case BPF_PROG_TYPE_TRACING:
> - switch (env->prog->expected_attach_type) {
> - case BPF_TRACE_FENTRY:
> - case BPF_TRACE_FEXIT:
> - case BPF_TRACE_FSESSION:
> - range = retval_range(0, 0);
> - break;
> - case BPF_TRACE_RAW_TP:
> - case BPF_MODIFY_RETURN:
> - return 0;
> - case BPF_TRACE_ITER:
> - break;
> - default:
> - return -ENOTSUPP;
> - }
> - break;
> - case BPF_PROG_TYPE_KPROBE:
> - switch (env->prog->expected_attach_type) {
> - case BPF_TRACE_KPROBE_SESSION:
> - case BPF_TRACE_UPROBE_SESSION:
> - range = retval_range(0, 1);
> - break;
> - default:
> - return 0;
> - }
> - break;
> - case BPF_PROG_TYPE_SK_LOOKUP:
> - range = retval_range(SK_DROP, SK_PASS);
> - break;
> + if (prog_type == BPF_PROG_TYPE_STRUCT_OPS && !ret_type)
> + return 0;
>
> - case BPF_PROG_TYPE_LSM:
> - if (env->prog->expected_attach_type != BPF_LSM_CGROUP) {
> - /* no range found, any return value is allowed */
> - if (!get_func_retval_range(env->prog, &range))
> - return 0;
> - /* no restricted range, any return value is allowed */
> - if (range.minval == S32_MIN && range.maxval == S32_MAX)
> - return 0;
> - return_32bit = true;
> - } else if (!env->prog->aux->attach_func_proto->type) {
> - /* Make sure programs that attach to void
> - * hooks don't try to modify return value.
> - */
> - range = retval_range(1, 1);
> - }
> - break;
> + if (prog_type == BPF_PROG_TYPE_CGROUP_SKB && (env->prog->expected_attach_type == BPF_CGROUP_INET_EGRESS))
> + enforce_attach_type_range = tnum_range(2, 3);
Note: I've kept the range and subsequent check as-is, but it's not actually
correct - the check below does tnum_in(enforce_attach_type_range,
var_off) when it should be tnum_overlap(). I will fix this in a separate
series since it definitely needs a selftest and is unrelated to void
globals.
>
> - case BPF_PROG_TYPE_NETFILTER:
> - range = retval_range(NF_DROP, NF_ACCEPT);
> - break;
> - case BPF_PROG_TYPE_STRUCT_OPS:
> - if (!ret_type)
> - return 0;
> - range = retval_range(0, 0);
> - break;
> - case BPF_PROG_TYPE_EXT:
> - /* freplace program can return anything as its return value
> - * depends on the to-be-replaced kernel func or bpf program.
> - */
> - default:
> + if (!return_retval_range(env, &range))
> return 0;
> - }
>
> enforce_retval:
> if (reg->type != SCALAR_VALUE) {
> @@ -18021,7 +18046,7 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
> if (err)
> return err;
>
> - if (!retval_range_within(range, reg, return_32bit)) {
> + if (!retval_range_within(range, reg)) {
> verbose_invalid_scalar(env, reg, range, exit_ctx, reg_name);
> if (!is_subprog &&
> prog->expected_attach_type == BPF_LSM_CGROUP &&
next prev parent reply other threads:[~2026-02-27 15:50 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-27 15:46 [PATCH bpf-next v5 0/5] bpf: Allow void return type for global subprogs Emil Tsalapatis
2026-02-27 15:46 ` [PATCH bpf-next v5 1/5] bpf: Factor out program return value calculation Emil Tsalapatis
2026-02-27 15:50 ` Emil Tsalapatis [this message]
2026-02-27 18:57 ` Eduard Zingerman
2026-02-28 0:36 ` Emil Tsalapatis
2026-02-27 20:27 ` kernel test robot
2026-02-27 20:49 ` kernel test robot
2026-02-28 1:22 ` kernel test robot
2026-02-27 15:46 ` [PATCH bpf-next v5 2/5] bpf: Extract program_returns_void() for clarity Emil Tsalapatis
2026-02-27 15:46 ` [PATCH bpf-next v5 3/5] bpf: extract check_subprogram_return_code() " Emil Tsalapatis
2026-02-27 19:42 ` Eduard Zingerman
2026-02-27 15:46 ` [PATCH bpf-next v5 4/5] bpf: Allow void global functions in the verifier Emil Tsalapatis
2026-02-27 16:24 ` bot+bpf-ci
2026-02-27 19:32 ` Eduard Zingerman
2026-02-28 0:39 ` Emil Tsalapatis
2026-02-27 15:46 ` [PATCH bpf-next v5 5/5] selftests: bpf: Add tests for void global subprogs Emil Tsalapatis
2026-02-27 19:53 ` Eduard Zingerman
2026-02-28 0:32 ` Emil Tsalapatis
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