On Tue, Jun 23, 2020 at 11:05:05AM +0200, Christoph Hellwig wrote:
> On Sat, Jun 20, 2020 at 07:16:16PM -0700, Andrew Morton wrote:
> > On Thu, 18 Jun 2020 08:43:06 +0200 Christoph Hellwig <hch@xxxxxx> wrote:
> >
> > > Use PAGE_KERNEL_ROX directly instead of allocating RWX and setting the
> > > page read-only just after the allocation.
> > >
> > > --- a/arch/arm64/kernel/probes/kprobes.c
> > > +++ b/arch/arm64/kernel/probes/kprobes.c
> > > @@ -120,15 +120,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
> > >
> > > void *alloc_insn_page(void)
> > > {
> > > - void *page;
> > > -
> > > - page = vmalloc_exec(PAGE_SIZE);
> > > - if (page) {
> > > - set_memory_ro((unsigned long)page, 1);
> > > - set_vm_flush_reset_perms(page);
> > > - }
> > > -
> > > - return page;
> > > + return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END,
> > > + GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS,
> > > + NUMA_NO_NODE, __func__);
> > > }
> > >
> > > /* arm kprobe: install breakpoint in text */
> >
> > But why. I think this is just a cleanup, doesn't address any runtime issue?
>
> It doesn't "fix" an issue - it just simplifies and speeds up the code.
Ok, but I don't understand the PLT comment from Peter in
20200618092754.GF576905@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx:
| I think this has the exact same range issue as the x86 user. But it
| might be less fatal if their PLT magic can cover the full range.
Peter, please could you elaborate on your concern? I feel like I'm missing
some context.
Cheers,
Will
