From: Matthew Wilcox <willy@infradead.org>
To: Jaewon Kim <jaewon31.kim@samsung.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
walken@google.com, bp@suse.de, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com
Subject: Re: [PATCH] mm: mmap: show vm_unmapped_area error log
Date: Sun, 8 Mar 2020 05:36:16 -0700 [thread overview]
Message-ID: <20200308123616.GH31215@bombadil.infradead.org> (raw)
In-Reply-To: <5E64C1D7.3000208@samsung.com>
On Sun, Mar 08, 2020 at 06:58:47PM +0900, Jaewon Kim wrote:
> On 2020년 03월 08일 10:58, Matthew Wilcox wrote:
> > On Sat, Mar 07, 2020 at 03:47:44PM -0800, Andrew Morton wrote:
> >> On Fri, 6 Mar 2020 15:16:22 +0900 Jaewon Kim <jaewon31.kim@samsung.com> wrote:
> >>> Even on 64 bit kernel, the mmap failure can happen for a 32 bit task.
> >>> Virtual memory space shortage of a task on mmap is reported to userspace
> >>> as -ENOMEM. It can be confused as physical memory shortage of overall
> >>> system.
> > But userspace can trigger this printk. We don't usually allow printks
> > under those circumstances, even ratelimited.
> Hello thank you your comment.
>
> Yes, userspace can trigger printk, but this was useful for to know why
> a userspace task was crashed. There seems to be still many userspace
> applications which did not check error of mmap and access invalid address.
>
> Additionally in my AARCH64 Android environment, display driver tries to
> get userspace address to map its display memory. The display driver
> report -ENOMEM from vm_unmapped_area and but also from GPU related
> address space.
>
> Please let me know your comment again if this debug is now allowed
> in that userspace triggered perspective.
The scenario that worries us is an attacker being able to fill the log
files and so also fill (eg) the /var partition. Once it's full, future
kernel messages cannot be stored anywhere and so there will be no traces
of their privilege escalation.
Maybe a tracepoint would be a better idea? Usually they are disabled,
but they can be enabled by a sysadmin to gain insight into why an
application is crashing.
next prev parent reply other threads:[~2020-03-08 12:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200304030211epcas1p4da8cb569947aefb3aad1da039aaabce4@epcas1p4.samsung.com>
2020-03-04 3:02 ` [PATCH] mm: mmap: show vm_unmapped_area error log Jaewon Kim
2020-03-05 1:35 ` Jaewon Kim
2020-03-06 4:24 ` Andrew Morton
2020-03-06 6:16 ` Jaewon Kim
2020-03-07 23:47 ` Andrew Morton
2020-03-08 1:58 ` Matthew Wilcox
2020-03-08 9:58 ` Jaewon Kim
2020-03-08 12:36 ` Matthew Wilcox [this message]
2020-03-09 9:12 ` Jaewon Kim
2020-03-09 14:01 ` Matthew Wilcox
2020-03-10 4:18 ` Jaewon Kim
2020-03-08 10:10 ` Jaewon Kim
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