On Fri, Jul 1, 2022 at 10:58 PM Yonghong Song <yhs@xxxxxx> wrote: > > > > 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@xxxxxxxxx> > > Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx> > > --- > > 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(). This seems wrong to use current_cred(). show_value is used to not "leak" pointer values to unprivileged user-space, right? In our case BPF iterator is privileged, so there is no need to hide (or mangle, didn't check) values. If it happens that a privileged process loads iter/ksym program and then passes prog FD to unprivileged one to read iterator output, iter/ksym should still get correct symbol values. I think the initial approach with show_value = true is the right one -- give all the information as it is to BPF iterator. > > > + > > + 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);
