Re: [PATCH 02/10] bpf: Add multi kprobe link

Jiri Olsa
2022-03-06T17:28:56Z

On Fri, Mar 04, 2022 at 03:11:01PM -0800, Andrii Nakryiko wrote:

SNIP

> > +static int
> > +kprobe_multi_resolve_syms(const void *usyms, u32 cnt,
> > + unsigned long *addrs)
> > +{
> > + unsigned long addr, size;
> > + const char **syms;
> > + int err = -ENOMEM;
> > + unsigned int i;
> > + char *func;
> > +
> > + size = cnt * sizeof(*syms);
> > + syms = kvzalloc(size, GFP_KERNEL);
> > + if (!syms)
> > + return -ENOMEM;
> > +
> > + func = kmalloc(KSYM_NAME_LEN, GFP_KERNEL);
> > + if (!func)
> > + goto error;
> > +
> > + if (copy_from_user(syms, usyms, size)) {
> > + err = -EFAULT;
> > + goto error;
> > + }
> > +
> > + for (i = 0; i < cnt; i++) {
> > + err = strncpy_from_user(func, syms[i], KSYM_NAME_LEN);
> > + if (err == KSYM_NAME_LEN)
> > + err = -E2BIG;
> > + if (err < 0)
> > + goto error;
> > +
> > + err = -EINVAL;
> > + if (func[0] == '\0')
> > + goto error;
>
> wouldn't empty string be handled by kallsyms_lookup_name?

it would scan and compare all symbols with empty string,
so it's better to test for it

jirka

>
> > + addr = kallsyms_lookup_name(func);
> > + if (!addr)
> > + goto error;
> > + if (!kallsyms_lookup_size_offset(addr, &size, NULL))
> > + size = MCOUNT_INSN_SIZE;
> > + addr = ftrace_location_range(addr, addr + size - 1);
> > + if (!addr)
> > + goto error;
> > + addrs[i] = addr;
> > + }
> > +
> > + err = 0;
> > +error:
> > + kvfree(syms);
> > + kfree(func);
> > + return err;
> > +}
> > +
>
> …