linux-kernel - Re: linux-next: not-present page at swap_vma

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Message-ID: <874ktl1p7y.fsf@yhuang-dev.intel.com>
Date:   Wed, 15 Apr 2020 10:01:53 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Qian Cai <cai@....pw>
Cc:     Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Minchan Kim <minchan@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: linux-next: not-present page at swap_vma_readahead()

Qian Cai <cai@....pw> writes:

>> On Apr 14, 2020, at 10:32 AM, Qian Cai <cai@....pw> wrote:
>> 
>> Fuzzers are unhappy. Thoughts?
>
> This is rather to reproduce. All the traces so far are from copy_from_user() to trigger a page fault,
> and then it dereferences a bad pte in swap_vma_readahead(),
>
> 	for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
> 	     i++, pte++) {
> 		pentry = *pte;   <— crashed here.
> 		if (pte_none(pentry))

Is it possible to bisect this?

Because the crash point is identified, it may be helpful to collect and
analyze the status of the faulting page table and readahead ptes.  But I
am not familiar with the ARM64 architecture.  So I cannot help much
here.

Best Regards,
Huang, Ying