linux-kernel - Re: [PATCH] x86: Fix memory leak of init_vdso

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Date:	Thu, 21 Jul 2011 15:39:06 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <ak@...ux.intel.com>, mingo@...hat.com,
	wzt <wzt.wzt@...il.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, tglx@...utronix.de, hpa@...or.com,
	Michal Hocko <mhocko@...e.cz>,
	Zhitong Wang <zhitong.wangzt@...baba-inc.com>
Subject: Re: [PATCH] x86: Fix memory leak of init_vdso_vars()

On Thu, Jul 21, 2011 at 2:38 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Andrew Lutomirski <luto@....edu> wrote:
>
>> On Thu, Jul 21, 2011 at 1:08 PM, Andi Kleen <ak@...ux.intel.com> wrote:
>> > On Thu, Jul 21, 2011 at 10:33:14AM -0400, Andy Lutomirski wrote:
>> >> From: Zhitong Wang <wzt.wzt@...il.com>
>> >>
>> >> If init_vdso_vars ran out of memory (not very likely), then it would
>> >> leak a few pages as well.
>> >>
>> >> Also rename init_vdso_vars to just init_vdso, since initializing
>> >> vvars is just about the only thing this function doesn't do.
>> >
>> > Just add a GFP_PANIC, there's no way to recover from this.
>> > Your system will not work without a vdso.
>>
>> Ingo objected to this before, although I'm not convinved.  Calling
>> init_vdso_vars more than once will cause major problems (like
>> double-patching of alternatives).  If there's too little memory for
>> it to work, then presumably there's also too little memory to start
>> init.
>>
>>  (Also, I bet that no one ever audited whether the ELF loader works
>> right if the vDSO failed to load.)
>>
>> Ingo?
>
> This assumes that the system actually needs an ELF loader - if a
> static binary is booted via a init= boot parameter it might not be
> needed.

I actually meant the kernel's loaded.  But I just looked and it appears correct.

But I think this whole thing is silly, because I can't see any good
reason that the vdso needs to allocate memory in the first place.
I'll send a patch.

--Andy
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