On Mon, 12 Sep 2016 21:07:40 -0400
David Long <dave.l...@linaro.org> wrote:
>
> After the patch the function reads as follows:
>
> > enum kprobe_insn __kprobes
> > arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn
> > *asi)
> > {
> > enum kprobe_insn decoded;
> > kprobe_opcode_t insn = le32_to_cpu(*addr);
> > kprobe_opcode_t *scan_end = NULL;
> > unsigned long size = 0, offset = 0;
> >
> > /*
> > * If there's a symbol defined in front of and near enough to
> > * the probe address assume it is the entry point to this
> > * code and use it to further limit how far back we search
> > * when determining if we're in an atomic sequence. If we could
> > * not find any symbol skip the atomic test altogether as we
> > * could otherwise end up searching irrelevant text/literals.
> > * KPROBES depends on KALLSYMS so this last case should never
> > * happen.
> > */
> > if (kallsyms_lookup_size_offset((unsigned long) addr, &size, &offset)) {
> > if (offset < (MAX_ATOMIC_CONTEXT_SIZE*sizeof(kprobe_opcode_t)))
> > scan_end = addr - (offset / sizeof(kprobe_opcode_t));
> > else
> > scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE;
> > }
> > decoded = arm_probe_decode_insn(insn, asi);
> >
> > if (decoded != INSN_REJECTED && scan_end)
> > if (is_probed_address_atomic(addr - 1, scan_end))
> > return INSN_REJECTED;
> >
> > return decoded;
> > }
>
> A failed kallsyms_lookup_size_offset() call means scan_end will be left
> as NULL, which in turn means arm_kprobe_decode_insn() will simply return
> the result of the arm_probe_decode_insn() call. In other words it does
> the normal analysis of the instruction to be probed, but does not do the
> atomic sequence search that normally follows that (since it doesn't
> really know how far back to search).
OK, my idea was just rejecting it when kallsyms_lookup_size_offset() is
failed, because we can not ensure that the address is in the kernel
text. But anyway, that should be tested in general code like kernel/kprobes.c.
OK, now I think it is clear to apply.
Acked-by: Masami Hiramatsu <mhira...@kernel.org>
Thanks,
>
> Thanks,
> -dl
>
--
Masami Hiramatsu <mhira...@kernel.org>
