Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: Minchan Kim <minchan@kernel.org>
To: Wang Nan <wangnan0@huawei.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	mhocko@kernel.org, will.deacon@arm.com,
	Bob Liu <liubo95@huawei.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	David Rientjes <rientjes@google.com>,
	Ingo Molnar <mingo@kernel.org>, Roman Gushchin <guro@fb.com>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [RESEND PATCH] mm, oom_reaper: gather each vma to prevent leaking TLB entry
Date: Fri, 10 Nov 2017 09:19:33 +0900
Message-ID: <20171110001933.GA12421@bbox> (raw)
In-Reply-To: <20171107095453.179940-1-wangnan0@huawei.com>

On Tue, Nov 07, 2017 at 09:54:53AM +0000, Wang Nan wrote:
> tlb_gather_mmu(&tlb, mm, 0, -1) means gathering the whole virtual memory
> space. In this case, tlb->fullmm is true. Some archs like arm64 doesn't
> flush TLB when tlb->fullmm is true:
> 
>   commit 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1").
> 
> Which makes leaking of tlb entries.

That means soft-dirty which has used tlb_gather_mmu with fullmm could be
broken via losing write-protection bit once it supports arm64 in future?

If so, it would be better to use TASK_SIZE rather than -1 in tlb_gather_mmu.
Of course, it's a off-topic.

However, I want to add a big fat comment in tlb_gather_mmu to warn "TLB
flushing with (0, -1) can be skipped on some architectures" so upcoming
users can care of.

Thanks.

> 
> Will clarifies his patch:
> 
> > Basically, we tag each address space with an ASID (PCID on x86) which
> > is resident in the TLB. This means we can elide TLB invalidation when
> > pulling down a full mm because we won't ever assign that ASID to another mm
> > without doing TLB invalidation elsewhere (which actually just nukes the
> > whole TLB).
> >
> > I think that means that we could potentially not fault on a kernel uaccess,
> > because we could hit in the TLB.
> 
> There could be a window between complete_signal() sending IPI to other
> cores and all threads sharing this mm are really kicked off from cores.
> In this window, the oom reaper may calls tlb_flush_mmu_tlbonly() to flush
> TLB then frees pages. However, due to the above problem, the TLB entries
> are not really flushed on arm64. Other threads are possible to access
> these pages through TLB entries. Moreover, a copy_to_user() can also
> write to these pages without generating page fault, causes use-after-free
> bugs.
> 
> This patch gathers each vma instead of gathering full vm space.
> In this case tlb->fullmm is not true. The behavior of oom reaper become
> similar to munmapping before do_exit, which should be safe for all archs.
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Cc: Bob Liu <liubo95@huawei.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Roman Gushchin <guro@fb.com>
> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> ---
>  mm/oom_kill.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index dee0f75..18c5b35 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -532,7 +532,6 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
>  	 */
>  	set_bit(MMF_UNSTABLE, &mm->flags);
>  
> -	tlb_gather_mmu(&tlb, mm, 0, -1);
>  	for (vma = mm->mmap ; vma; vma = vma->vm_next) {
>  		if (!can_madv_dontneed_vma(vma))
>  			continue;
> @@ -547,11 +546,13 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
>  		 * we do not want to block exit_mmap by keeping mm ref
>  		 * count elevated without a good reason.
>  		 */
> -		if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
> +		if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
> +			tlb_gather_mmu(&tlb, mm, vma->vm_start, vma->vm_end);
>  			unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
>  					 NULL);
> +			tlb_finish_mmu(&tlb, vma->vm_start, vma->vm_end);
> +		}
>  	}
> -	tlb_finish_mmu(&tlb, 0, -1);
>  	pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
>  			task_pid_nr(tsk), tsk->comm,
>  			K(get_mm_counter(mm, MM_ANONPAGES)),
> -- 
> 2.10.1
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  parent reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-07  9:54 Wang Nan
2017-11-07 10:09 ` Michal Hocko
2017-11-10  0:19 ` Minchan Kim [this message]
2017-11-10 10:15   ` Michal Hocko
2017-11-10 12:26     ` [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy (was: Re: [RESEND PATCH] mm, oom_reaper: gather each vma to prevent) " Michal Hocko
2017-11-13  0:28       ` Minchan Kim
2017-11-13  9:51         ` Michal Hocko
2017-11-14  1:45           ` Minchan Kim
2017-11-14  7:21             ` Michal Hocko
2017-11-15  0:12               ` Minchan Kim
2017-11-15  8:14         ` Michal Hocko
2017-11-16  0:44           ` Minchan Kim
2017-11-16  9:19             ` Michal Hocko
2017-11-15 17:33       ` Will Deacon
2017-11-16  9:20         ` Michal Hocko
2017-11-20 14:24           ` Will Deacon
2017-11-20 16:04             ` [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy Michal Hocko
2017-11-22 19:30               ` Will Deacon
2017-11-23  6:18                 ` Minchan Kim

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20171110001933.GA12421@bbox \
    --to=minchan@kernel.org \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=guro@fb.com \
    --cc=khlebnikov@yandex-team.ru \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=liubo95@huawei.com \
    --cc=mhocko@kernel.org \
    --cc=mhocko@suse.com \
    --cc=mingo@kernel.org \
    --cc=rientjes@google.com \
    --cc=wangnan0@huawei.com \
    --cc=will.deacon@arm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git