linux-kernel - Re: [PATCH] kprobes: Allow both @symbol

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Date:   Tue, 15 Mar 2022 21:56:00 +0800
From:   李棒 <libang.linuxer@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     naveen.n.rao@...ux.ibm.com, anil.s.keshavamurthy@...el.com,
        davem@...emloft.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kprobes: Allow both @symbol_name and @addr to exist

On Sun, Mar 13, 2022 at 4:36 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Sun, 13 Mar 2022 11:21:25 +0800
> Bang Li <libang.linuxer@...il.com> wrote:
>
> > If the address found by the @symbol_name is equal to the @addr, this case
> > should be considered a valid parameter combinations.
>
> Could you tell me the reason why this is needed and use case?
> I explictly made this case as an error, because I couldn't find
> any good reason to support this case.
>
> Thank you,
>

I'm not sure if I need to change it this way, I just think it's more
comprehensive.

Thanks

> >
> > Example:
> >
> > static struct kprobe kp = {
> >     .symbol_name    = "kernel_clone",
> >     .addr           = (kprobe_opcode_t*)kernel_clone,
> > };
> >
> > Signed-off-by: Bang Li <libang.linuxer@...il.com>
> > ---
> >  kernel/kprobes.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 94cab8c9ce56..70d4ed9e7dc7 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1497,13 +1497,19 @@ bool within_kprobe_blacklist(unsigned long addr)
> >  static kprobe_opcode_t *_kprobe_addr(kprobe_opcode_t *addr,
> >                       const char *symbol_name, unsigned int offset)
> >  {
> > -     if ((symbol_name && addr) || (!symbol_name && !addr))
> > +     kprobe_opcode_t *symbol_addr;
> > +
> > +     if (!symbol_name && !addr)
> >               goto invalid;
> >
> >       if (symbol_name) {
> > -             addr = kprobe_lookup_name(symbol_name, offset);
> > -             if (!addr)
> > +             symbol_addr = kprobe_lookup_name(symbol_name, offset);
> > +             if (!symbol_addr)
> >                       return ERR_PTR(-ENOENT);
> > +
> > +             if (addr && symbol_addr != addr)
> > +                     goto invalid;
> > +             addr = symbol_addr;
> >       }
> >
> >       addr = (kprobe_opcode_t *)(((char *)addr) + offset);
> > @@ -2062,8 +2068,7 @@ bool __weak arch_kprobe_on_func_entry(unsigned long offset)
> >   * function entry address or not.
> >   * This returns 0 if it is the function entry, or -EINVAL if it is not.
> >   * And also it returns -ENOENT if it fails the symbol or address lookup.
> > - * Caller must pass @addr or @sym (either one must be NULL), or this
> > - * returns -EINVAL.
> > + * Caller must pass @addr or @sym, or this returns -EINVAL.
> >   */
> >  int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset)
> >  {
> > --
> > 2.25.1
> >
>
>
> --
> Masami Hiramatsu <mhiramat@...nel.org>