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Message-ID: <CAGXu5j+w0mHMSjcwRcQuyvfRa+XSy2zs7kLYj+qNpnokfSwb3A@mail.gmail.com>
Date: Mon, 24 Sep 2018 13:03:33 -0700
From: Kees Cook <keescook@...omium.org>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>, "jannh@...gle.com" <jannh@...gle.com>,
"arjan@...ux.intel.com" <arjan@...ux.intel.com>, "tglx@...utronix.de" <tglx@...utronix.de>,
"linux-mm@...ck.org" <linux-mm@...ck.org>, "x86@...nel.org" <x86@...nel.org>,
"kristen@...ux.intel.com" <kristen@...ux.intel.com>, "hpa@...or.com" <hpa@...or.com>,
"mingo@...hat.com" <mingo@...hat.com>,
"alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
"Hansen, Dave" <dave.hansen@...el.com>
Subject: Re: [PATCH v6 3/4] vmalloc: Add debugfs modfraginfo
On Mon, Sep 24, 2018 at 11:58 AM, Edgecombe, Rick P
<rick.p.edgecombe@...el.com> wrote:
> On Fri, 2018-09-21 at 11:56 -0700, Kees Cook wrote:
>> On Thu, Sep 13, 2018 at 2:31 PM, Rick Edgecombe
>> <rick.p.edgecombe@...el.com> wrote:
>> > +done:
>> > + gap = (MODULES_END - last_end);
>> > + if (gap > largest_free)
>> > + largest_free = gap;
>> > + total_free += gap;
>> > +
>> > + spin_unlock(&vmap_area_lock);
>> > +
>> > + seq_printf(m, "\tLargest free space:\t%lu kB\n", largest_free /
>> > 1024);
>> > + seq_printf(m, "\t Total free space:\t%lu kB\n", total_free / 1024);
>> > +
>> > + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && kaslr_enabled())
>> > + seq_printf(m, "Allocations in backup area:\t%lu\n",
>> > backup_cnt);
>> I don't think the IS_ENABLED is needed here?
> The reason for this is that for ARCH=um, CONFIG_X86_64 is defined but
> kaslr_enabled is not. kaslr_enabled is declared above to protect against a
> compiler error.
>
> So IS_ENABLED(CONFIG_RANDOMIZE_BASE) is protecting kaslr_enabled from causing a
> linker error. It gets constant evaluated to 0 and the compiler optimizes out the
> kaslr_enabled call. Thought it was better to guard with CONFIG_RANDOMIZE_BASE
> than with CONFIG_UM, to try to catch the broader situation. I guess I could move
> it to a helper inside ifdefs instead. Was trying to keep the ifdef-ed code down.
Ah yes, UM. Perhaps kaslr_enabled() could be defined somewhere so that
it would link sanely? (Maybe in module.h?)
>> I wonder if there is a better way to arrange this code that uses fewer
>> ifdefs, etc. Maybe a single CONFIG that capture whether or not
>> fine-grained module randomization is built in, like:
>>
>> config RANDOMIZE_FINE_MODULE
>> def_bool y if RANDOMIZE_BASE && X86_64
>>
>> #ifdef CONFIG_RANDOMIZE_FINE_MODULE
>> ...
>> #endif
>>
>> But that doesn't capture the DEBUG_FS and PROC_FS bits ... so ...
>> maybe not worth it. I guess, either way:
> Hmmm, didn't know about that. Would clean it up some at least.
>
> I wish the debugfs info could be in module.c to help with this IFDEFs, but it
> needs vmalloc internals. MODULES_VADDR is not standardized across the ARCH's as
> well, so this was my best attempt to implement this without having to make
> changes in other architectures.
Yeah, I've long wanted to try to sandardize the module+vmalloc guts,
but it's just different enough in each architecture that it eludes
people.
-Kees
--
Kees Cook
Pixel Security
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