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Marchesi" , , "Martin KaFai Lau" Subject: Re: [PATCH bpf-next v6 04/17] bpf: Prepare verifier logs for upcoming kfunc stack arguments From: "Alexei Starovoitov" To: "Yonghong Song" , X-Mailer: aerc References: <20260419163316.731019-1-yonghong.song@linux.dev> <20260419163336.733654-1-yonghong.song@linux.dev> In-Reply-To: <20260419163336.733654-1-yonghong.song@linux.dev> On Sun Apr 19, 2026 at 9:33 AM PDT, Yonghong Song wrote: > This change prepares verifier log reporting for upcoming kfunc stack > argument support. > > Today verifier log code mostly assumes that an argument can be described > directly by a register number. That works for arguments passed in `R1` > to `R5`, but it does not work once kfunc arguments can also be > passed on the stack. > > Introduce an internal `argno` representation such that register-passed > arguments keep using their real register numbers, while stack-passed > arguments use an encoded value above a dedicated base. > `reg_arg_name()` converts this representation into either `R%d` or > `*(R11-off)` when emitting verifier logs. If a particular `argno` > is corresponding to a stack argument, print `*(R11-off)`. Otherwise, > print `R%d`. Here R11 presents the base of stack arguments. > > This keeps existing logs readable for register arguments and allows the > same log sites to handle future stack arguments without open-coding > special cases. > > Update selftests accordingly. > > Signed-off-by: Yonghong Song > --- > include/linux/bpf_verifier.h | 1 + > kernel/bpf/verifier.c | 649 ++++++++++-------- > .../testing/selftests/bpf/prog_tests/bpf_nf.c | 22 +- > .../selftests/bpf/prog_tests/cb_refs.c | 2 +- > .../selftests/bpf/prog_tests/kfunc_call.c | 2 +- > .../selftests/bpf/prog_tests/linked_list.c | 4 +- > .../selftests/bpf/progs/cgrp_kfunc_failure.c | 14 +- > .../selftests/bpf/progs/cpumask_failure.c | 10 +- > .../testing/selftests/bpf/progs/dynptr_fail.c | 22 +- > .../selftests/bpf/progs/file_reader_fail.c | 4 +- > tools/testing/selftests/bpf/progs/irq.c | 4 +- > tools/testing/selftests/bpf/progs/iters.c | 6 +- > .../selftests/bpf/progs/iters_state_safety.c | 14 +- > .../selftests/bpf/progs/iters_testmod.c | 4 +- > .../selftests/bpf/progs/iters_testmod_seq.c | 4 +- > .../selftests/bpf/progs/map_kptr_fail.c | 2 +- > .../selftests/bpf/progs/percpu_alloc_fail.c | 4 +- > .../testing/selftests/bpf/progs/rbtree_fail.c | 6 +- > .../bpf/progs/refcounted_kptr_fail.c | 2 +- > .../testing/selftests/bpf/progs/stream_fail.c | 2 +- > .../selftests/bpf/progs/task_kfunc_failure.c | 18 +- > .../selftests/bpf/progs/task_work_fail.c | 6 +- > .../selftests/bpf/progs/test_bpf_nf_fail.c | 8 +- > .../bpf/progs/test_kfunc_dynptr_param.c | 2 +- > .../bpf/progs/test_kfunc_param_nullable.c | 2 +- > .../selftests/bpf/progs/verifier_bits_iter.c | 4 +- > .../bpf/progs/verifier_ref_tracking.c | 6 +- > .../selftests/bpf/progs/verifier_vfs_reject.c | 8 +- > .../testing/selftests/bpf/progs/wq_failures.c | 2 +- > tools/testing/selftests/bpf/verifier/calls.c | 14 +- > 30 files changed, 474 insertions(+), 374 deletions(-) > > diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h > index b148f816f25b..9fbbddc40d21 100644 > --- a/include/linux/bpf_verifier.h > +++ b/include/linux/bpf_verifier.h > @@ -913,6 +913,7 @@ struct bpf_verifier_env { > * e.g., in reg_type_str() to generate reg_type string > */ > char tmp_str_buf[TMP_STR_BUF_LEN]; > + char tmp_reg_arg_name_buf[32]; the name is too long. Just tmp_arg_name ? > struct bpf_insn insn_buf[INSN_BUF_SIZE]; > struct bpf_insn epilogue_buf[INSN_BUF_SIZE]; > struct bpf_scc_callchain callchain_buf; > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 3716d9688d00..6aa4dc161a56 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -1751,6 +1751,55 @@ static struct bpf_verifier_state *push_stack(struc= t bpf_verifier_env *env, > return &elem->st; > } > =20 > +/* > + * Unified argument number encoding for verifier log messages. > + * Register args (arg_idx 0-4) use their register number (R1-R5). > + * Stack args (arg_idx 5+) are encoded as STACK_ARGNO_BASE + arg_idx > + * to avoid collision with register numbers. reg_arg_name() decodes > + * this back to a human-readable string like "*(R11-8)" for logs. > + */ > +#define STACK_ARGNO_BASE 100 > + > +static bool is_stack_argno(int argno) > +{ > + return argno >=3D STACK_ARGNO_BASE; > +} > + > +static u32 make_argno(u32 arg_idx) > +{ > + if (arg_idx < MAX_BPF_FUNC_REG_ARGS) > + return BPF_REG_1 + arg_idx; > + return STACK_ARGNO_BASE + arg_idx; > +} > + > +static u32 arg_idx_from_argno(int argno) > +{ > + if (is_stack_argno(argno)) > + return argno - STACK_ARGNO_BASE; > + return argno - BPF_REG_1; > +} > + > +static int next_argno(int argno) > +{ > + return make_argno(arg_idx_from_argno(argno) + 1); > +} I don't like this +1, -1 dance all around. Makes the whole thing hard to follow. Keep argno starting at 1. So old regno =3D=3D argno. > /* Check if local kptr in src arg matches kptr in dst arg */ > - if (meta->func_id =3D=3D BPF_FUNC_kptr_xchg && regno =3D=3D BPF_REG_2)= { > - if (map_kptr_match_type(env, meta->kptr_field, reg, regno)) > + if (meta->func_id =3D=3D BPF_FUNC_kptr_xchg && > + !is_stack_argno(argno) && argno =3D=3D BPF_REG_2) { > + if (map_kptr_match_type(env, meta->kptr_field, reg, argno)) And then this argno =3D=3D BPF_REG_2 will look fine. With argno base 0 the above looks broken. Also is_stack_argno() looks like defensive programming. remove it.