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SubjectRe: [PATCH v2 bpf-next 1/2] bpf: add a ksym BPF iterator
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On 7/1/22 2:26 AM, Alan Maguire wrote:
> add a "ksym" iterator which provides access to a "struct kallsym_iter"
> for each symbol. Intent is to support more flexible symbol parsing
> as discussed in [1].
>
> [1] https://lore.kernel.org/all/YjRPZj6Z8vuLeEZo@krava/
>
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
> kernel/kallsyms.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 89 insertions(+)
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index fbdf8d3..8b662da 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -30,6 +30,7 @@
> #include <linux/module.h>
> #include <linux/kernel.h>
> #include <linux/bsearch.h>
> +#include <linux/btf_ids.h>
>
> /*
> * These will be re-linked against their real values
> @@ -799,6 +800,91 @@ static int s_show(struct seq_file *m, void *p)
> .show = s_show
> };
>
> +#ifdef CONFIG_BPF_SYSCALL
> +
> +struct bpf_iter__ksym {
> + __bpf_md_ptr(struct bpf_iter_meta *, meta);
> + __bpf_md_ptr(struct kallsym_iter *, ksym);
> +};
> +
> +static int ksym_prog_seq_show(struct seq_file *m, bool in_stop)
> +{
> + struct bpf_iter__ksym ctx;
> + struct bpf_iter_meta meta;
> + struct bpf_prog *prog;
> +
> + meta.seq = m;
> + prog = bpf_iter_get_info(&meta, in_stop);
> + if (!prog)
> + return 0;
> +
> + ctx.meta = &meta;
> + ctx.ksym = m ? m->private : NULL;
> + return bpf_iter_run_prog(prog, &ctx);
> +}
> +
> +static int bpf_iter_ksym_seq_show(struct seq_file *m, void *p)
> +{
> + return ksym_prog_seq_show(m, false);
> +}
> +
> +static void bpf_iter_ksym_seq_stop(struct seq_file *m, void *p)
> +{
> + if (!p)
> + (void) ksym_prog_seq_show(m, true);
> + else
> + s_stop(m, p);
> +}
> +
> +static const struct seq_operations bpf_iter_ksym_ops = {
> + .start = s_start,
> + .next = s_next,
> + .stop = bpf_iter_ksym_seq_stop,
> + .show = bpf_iter_ksym_seq_show,
> +};
> +
> +static int bpf_iter_ksym_init(void *priv_data, struct bpf_iter_aux_info *aux)
> +{
> + struct kallsym_iter *iter = priv_data;
> +
> + reset_iter(iter, 0);
> +
> + iter->show_value = true;

I think instead of always having show_value = true, we should have
iter->show_value = kallsyms_show_value(...);

this is consistent with what `cat /proc/kallsyms` is doing, and
also consistent with bpf_dump_raw_ok() used when dumping various
kernel info in syscall.c.

We don't have a file here, so credential can be from the current
process with current_cred().

> +
> + return 0;
> +}
> +
> +DEFINE_BPF_ITER_FUNC(ksym, struct bpf_iter_meta *meta, struct kallsym_iter *ksym)
> +
> +static const struct bpf_iter_seq_info ksym_iter_seq_info = {
> + .seq_ops = &bpf_iter_ksym_ops,
> + .init_seq_private = bpf_iter_ksym_init,
> + .fini_seq_private = NULL,
> + .seq_priv_size = sizeof(struct kallsym_iter),
> +};
> +
> +static struct bpf_iter_reg ksym_iter_reg_info = {
> + .target = "ksym",
> + .ctx_arg_info_size = 1,
> + .ctx_arg_info = {
> + { offsetof(struct bpf_iter__ksym, ksym),
> + PTR_TO_BTF_ID_OR_NULL },
> + },
> + .seq_info = &ksym_iter_seq_info,
> +};
> +
> +BTF_ID_LIST(btf_ksym_iter_id)
> +BTF_ID(struct, kallsym_iter)
> +
> +static void __init bpf_ksym_iter_register(void)
> +{
> + ksym_iter_reg_info.ctx_arg_info[0].btf_id = *btf_ksym_iter_id;
> + if (bpf_iter_reg_target(&ksym_iter_reg_info))
> + pr_warn("Warning: could not register bpf ksym iterator\n");
> +}
> +
> +#endif /* CONFIG_BPF_SYSCALL */
> +
> static inline int kallsyms_for_perf(void)
> {
> #ifdef CONFIG_PERF_EVENTS
> @@ -885,6 +971,9 @@ const char *kdb_walk_kallsyms(loff_t *pos)
> static int __init kallsyms_init(void)
> {
> proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
> +#if defined(CONFIG_BPF_SYSCALL)
> + bpf_ksym_iter_register();

You can inline this function here and if bpf_iter_reg_target(...)
failed, just return the error code.

> +#endif
> return 0;
> }
> device_initcall(kallsyms_init);

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