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bpf: Add support for __prog argument suffix to pass in prog->aux

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Instead of hardcoding the list of kfuncs that need prog->aux passed to
them with a combination of fixup_kfunc_call adjustment + __ign suffix,
combine both in __prog suffix, which ignores the argument passed in, and
fixes it up to the prog->aux. This allows kfuncs to have the prog->aux
passed into them without having to touch the verifier.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250513142812.1021591-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2025-05-13 07:28:12 -07:00 committed by Alexei Starovoitov
parent 3880cdbed1
commit bc049387b4
4 changed files with 47 additions and 8 deletions
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17
Documentation/bpf/kfuncs.rst
View File

@ -160,6 +160,23 @@ Or::
...
}
2.2.6 __prog Annotation
---------------------------
This annotation is used to indicate that the argument needs to be fixed up to
the bpf_prog_aux of the caller BPF program. Any value passed into this argument
is ignored, and rewritten by the verifier.
An example is given below::
__bpf_kfunc int bpf_wq_set_callback_impl(struct bpf_wq *wq,
int (callback_fn)(void *map, int *key, void *value),
unsigned int flags,
void *aux__prog)
{
struct bpf_prog_aux *aux = aux__prog;
...
}
.. _BPF_kfunc_nodef:
2.3 Using an existing kernel function

1
include/linux/bpf_verifier.h
View File

@ -591,6 +591,7 @@ struct bpf_insn_aux_data {
* bpf_fastcall pattern.
*/
u8 fastcall_spills_num:3;
u8 arg_prog:4;
/* below fields are initialized once */
unsigned int orig_idx; /* original instruction index */

4
kernel/bpf/helpers.c
View File

@ -3002,9 +3002,9 @@ __bpf_kfunc int bpf_wq_start(struct bpf_wq *wq, unsigned int flags)
__bpf_kfunc int bpf_wq_set_callback_impl(struct bpf_wq *wq,
int (callback_fn)(void *map, int *key, void *value),
unsigned int flags,
void *aux__ign)
void *aux__prog)
{
struct bpf_prog_aux *aux = (struct bpf_prog_aux *)aux__ign;
struct bpf_prog_aux *aux = (struct bpf_prog_aux *)aux__prog;
struct bpf_async_kern *async = (struct bpf_async_kern *)wq;
if (flags)

33
kernel/bpf/verifier.c
View File

@ -322,6 +322,7 @@ struct bpf_kfunc_call_arg_meta {
struct btf *arg_btf;
u32 arg_btf_id;
bool arg_owning_ref;
bool arg_prog;
struct {
struct btf_field *field;
@ -11897,6 +11898,11 @@ static bool is_kfunc_arg_irq_flag(const struct btf *btf, const struct btf_param
return btf_param_match_suffix(btf, arg, "__irq_flag");
}
static bool is_kfunc_arg_prog(const struct btf *btf, const struct btf_param *arg)
{
return btf_param_match_suffix(btf, arg, "__prog");
}
static bool is_kfunc_arg_scalar_with_name(const struct btf *btf,
const struct btf_param *arg,
const char *name)
@ -12938,6 +12944,17 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
if (is_kfunc_arg_ignore(btf, &args[i]))
continue;
if (is_kfunc_arg_prog(btf, &args[i])) {
/* Used to reject repeated use of __prog. */
if (meta->arg_prog) {
verbose(env, "Only 1 prog->aux argument supported per-kfunc\n");
return -EFAULT;
}
meta->arg_prog = true;
cur_aux(env)->arg_prog = regno;
continue;
}
if (btf_type_is_scalar(t)) {
if (reg->type != SCALAR_VALUE) {
verbose(env, "R%d is not a scalar\n", regno);
@ -21517,13 +21534,17 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
desc->func_id == special_kfunc_list[KF_bpf_rdonly_cast]) {
insn_buf[0] = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1);
*cnt = 1;
} else if (is_bpf_wq_set_callback_impl_kfunc(desc->func_id)) {
struct bpf_insn ld_addrs[2] = { BPF_LD_IMM64(BPF_REG_4, (long)env->prog->aux) };
}
insn_buf[0] = ld_addrs[0];
insn_buf[1] = ld_addrs[1];
insn_buf[2] = *insn;
*cnt = 3;
if (env->insn_aux_data[insn_idx].arg_prog) {
u32 regno = env->insn_aux_data[insn_idx].arg_prog;
struct bpf_insn ld_addrs[2] = { BPF_LD_IMM64(regno, (long)env->prog->aux) };
int idx = *cnt;
insn_buf[idx++] = ld_addrs[0];
insn_buf[idx++] = ld_addrs[1];
insn_buf[idx++] = *insn;
*cnt = idx;
}
return 0;
}