linux-kernel - Re: [PATCH v2 1/5] binfmt_elf_fdpic: Stop using dump

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Date:   Tue, 5 May 2020 13:42:12 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mark Salter <msalter@...hat.com>,
        Aurelien Jacquiot <jacquiot.aurelien@...il.com>,
        linux-c6x-dev@...ux-c6x.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Linux-sh list <linux-sh@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] binfmt_elf_fdpic: Stop using dump_emit() on user
 pointers on !MMU

On Tue, May 5, 2020 at 12:48 PM Christoph Hellwig <hch@....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?