linux-kernel - Re: [PATCH] platform/x86: wmi: Do not mix pages and kmalloc

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Message-ID: <20180621001721.GB3250@fury>
Date:   Wed, 20 Jun 2018 17:17:21 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andy@...radead.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Mihai Donțu <mihai.dontu@...il.com>,
        Mario.Limonciello@...l.com
Subject: Re: [PATCH] platform/x86: wmi: Do not mix pages and kmalloc

On Wed, Jun 20, 2018 at 04:43:14PM -0700, Kees Cook wrote:
> On Wed, Jun 20, 2018 at 4:37 PM, Darren Hart <dvhart@...radead.org> wrote:
> > On Wed, Jun 20, 2018 at 02:31:41PM -0700, Kees Cook wrote:
> >> The probe handler_data was being allocated with __get_free_pages()
> >> for no reason I could find. The error path was using kfree(). Since
> >
> > v4 of Mario's series used kmalloc:
> > https://patchwork.kernel.org/patch/9985827/
> >
> > This was changed in v10 to use __get_free_pages:
> > https://patchwork.kernel.org/patch/10018023/
> >
> > But... I'm not finding the discussion that led to this change.... Mario,
> > do you recall? Something about contiguous memory? We had a similar
> > discussion on an earlier series:
> >
> > https://patchwork.kernel.org/patch/9975277/
> 
> FWIW, kmalloc gets you contiguous memory...

Yeah, I'm not finding a valid reason to use __get_free_pages over kmalloc in
this case. I'll give Mario a chance to respond in case I'm just missing
something, but otherwise will plan to apply this patch.

> 
> But if the reason is found and needs to stay, the probe error path's
> kfree() needs to be fixed, and __GFP_COMP needs to be added to the
> free page flags.

Got it, thanks Kees.

-- 
Darren Hart
VMware Open Source Technology Center