Re: [PATCH v2 1/5] binfmt_elf_fdpic: Stop using dump_emit() on user pointers on !MMU

Christoph Hellwig
2020-05-05T12:15:57Z

On Tue, May 05, 2020 at 01:42:12PM +0200, Jann Horn wrote:
> On Tue, May 5, 2020 at 12:48 PM Christoph Hellwig <hch@lst.de> wrote:
> > On Wed, Apr 29, 2020 at 11:49:50PM +0200, Jann Horn wrote:
> > > dump_emit() is for kernel pointers, and VMAs describe userspace memory.
> > > Let's be tidy here and avoid accessing userspace pointers under KERNEL_DS,
> > > even if it probably doesn't matter much on !MMU systems - especially given
> > > that it looks like we can just use the same get_dump_page() as on MMU if
> > > we move it out of the CONFIG_MMU block.
> >
> > Looks sensible. Did you get a chance to test this with a nommu setup?
>
> Nope. Do you happen to have a recommendation for a convenient
> environment I can use with QEMU, or something like that? I'm guessing
> that just running a standard armel Debian userspace with a !mmu ARM
> kernel wouldn't work so well?

Nommu generally needs special userspace either using uclibc-ng or musl.
When I did the RISC-V nommu work I used buildroot for my root file
systems. We haven't gotten elffdpic to work on RISC-V yet, so I can't
use that setup for testing, but it should support ARM as well.