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From: Song Liu <songliubraving@fb.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"matthew.wilcox@oracle.com" <matthew.wilcox@oracle.com>,
	"kirill.shutemov@linux.intel.com"
	<kirill.shutemov@linux.intel.com>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"Kernel Team" <Kernel-team@fb.com>,
	"william.kucharski@oracle.com" <william.kucharski@oracle.com>
Subject: Re: [PATCH v8 2/4] uprobe: use original page when all uprobes are removed
Date: Fri, 26 Jul 2019 06:07:21 +0000	[thread overview]
Message-ID: <A6BFA766-141D-445E-8F64-BE8E50C4AC0E@fb.com> (raw)
In-Reply-To: <A0D24D6F-B649-4B4B-8C33-70B7DCB0D814@fb.com>


Hi Oleg, 

>> 
>> No. Yes, deny_write_access() protects mm->exe_file, but not the dynamic
>> libraries or other files which can be mmaped.
> 
> I see. Let me see how we can cover this. 
> 
>> 
>>>> and I am worried this code can try to lock the same page twice...
>>>> Say, the probed application does MADV_DONTNEED and then writes "int3"
>>>> into vma->vm_file at the same address to fool verify_opcode().
>>>> 
>>> 
>>> Do you mean the case where old_page == new_page?
>> 
>> Yes,
>> 
>>> I think this won't
>>> happen, because in uprobe_write_opcode() we only do orig_page for
>>> !is_register case.
>> 
>> See above.
>> 
>> !is_register doesn't necessarily mean the original page was previously cow'ed.
>> And even if it was cow'ed, MADV_DONTNEED can restore the original mapping.
> 
> I guess I know the case now. We can probably avoid this with an simp\x10le 
> check for old_page == new_page?

I decided to follow your suggestion of "unmap old_page; fault in orig_page". 
Please see v9 of the set. 

Thanks,
Song


  reply	other threads:[~2019-07-26  6:08 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-24  8:35 [PATCH v8 0/4] THP aware uprobe Song Liu
2019-07-24  8:35 ` [PATCH v8 1/4] mm: move memcmp_pages() and pages_identical() Song Liu
2019-07-24  8:35 ` [PATCH v8 2/4] uprobe: use original page when all uprobes are removed Song Liu
2019-07-24  9:07   ` Oleg Nesterov
2019-07-24  9:17     ` Oleg Nesterov
2019-07-24  9:20       ` Song Liu
2019-07-24 11:37   ` Oleg Nesterov
2019-07-24 18:52     ` Song Liu
2019-07-25  8:14       ` Oleg Nesterov
2019-07-25 18:17         ` Song Liu
2019-07-26  6:07           ` Song Liu [this message]
2019-07-26  8:44           ` Oleg Nesterov
2019-07-26 21:19             ` Song Liu
2019-07-24  8:35 ` [PATCH v8 3/4] mm, thp: introduce FOLL_SPLIT_PMD Song Liu
2019-07-24  8:36 ` [PATCH v8 4/4] uprobe: use FOLL_SPLIT_PMD instead of FOLL_SPLIT Song Liu

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