linux-kernel - Re: [PATCH 10/11] pstore/ram: Switch to persistent

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Date:	Wed, 16 May 2012 05:44:23 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Colin Cross <ccross@...roid.com>,
	Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>, arve@...roid.com,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	Jesper Juhl <jj@...osbits.net>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Thomas Meyer <thomas@...3r.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com
Subject: Re: [PATCH 10/11] pstore/ram: Switch to persistent_ram routines

On Tue, May 15, 2012 at 11:14 PM, Anton Vorontsov
<anton.vorontsov@...aro.org> wrote:
> Hello Kees,
>
> On Mon, May 14, 2012 at 03:21:17PM -0700, Kees Cook wrote:
> [...]
>> > -       buf = cxt->virt_addr + (id * cxt->record_size);
>> > -       memset(buf, '\0', cxt->record_size);
>> > +       persistent_ram_free_old(cxt->przs[id]);
>>
>> Hm, I don't think persistent_ram_free_old() is what's wanted here.
>> That appears to entirely release the region? I want to make sure the
>> memory is cleared first. And will this area come back on a write, or
>> does it stay released?
>
> It just releases ECC-restored memory region (a copy). The original
> (persistent) region is still fully reusable after that call.

Ah-ha, okay. So this still needs to clear the memory in the "real"
copy then. Thanks for the clarification.

>> > +       }
>> > +
>> > +       for (i = 0; i < cxt->max_count; i++) {
>> > +               size_t sz = cxt->record_size;
>> > +               phys_addr_t start = cxt->phys_addr + sz * i;
>> > +
>> > +               cxt->przs[i] = persistent_ram_new(start, sz, 0);
>>
>> persistent_ram_new() is marked as __init, so this is unsafe to call if
>> built as a module. I think persistent_ram_new() will need to lose the
>> __init marking, or I'm misunderstanding something.
>
> Um. ramoops' probe routine is also __init. persistent_ram_new is a
> part of ramoops module, so their __init functions will be discarded
> at the same time.
>
> ram_console can't be a module, so it is also fine.
>
> So I think it's all fine.

This is what I get for staring at patches instead of applying them. :)
Yeah, if it's all built together, it's no problem. It looked to me
like they were in different modules.

>> > +fail_przs:
>> > +       for (i = 0; cxt->przs[i]; i++)
>> > +               persistent_ram_free(cxt->przs[i]);
>>
>> This can lead to a BUG, since persistent_ram_free() doesn't handle
>> NULL arguments.
>
> The for loop has 'cxt->przs[i]' condition. :-)

Okay, fair enough. :)

> Thanks for the review!

Sure thing! Thanks for doing this work; I'm excited to have access in
ramoops to the new interfaces. :)

-Kees

-- 
Kees Cook
Chrome OS Security
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