linux-kernel - Re: [PATCH v4 4/8] arm: use fixmap for text patching when text is RO

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAGXu5jJJyLkw38VyZ6fuKf5k5EcQNf+Ke0G0=qZ+pc+CptvXmA@mail.gmail.com>
Date:	Thu, 4 Sep 2014 07:00:31 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Will Deacon <will.deacon@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rabin Vincent <rabin@....in>, Rob Herring <robh@...nel.org>,
	Laura Abbott <lauraa@...eaurora.org>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"msalter@...hat.com" <msalter@...hat.com>,
	Liu hua <sdu.liu@...wei.com>,
	Nikolay Borisov <Nikolay.Borisov@....com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Tomasz Figa <t.figa@...sung.com>,
	Doug Anderson <dianders@...gle.com>,
	Jason Wessel <jason.wessel@...driver.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4 4/8] arm: use fixmap for text patching when text is RO

On Thu, Sep 4, 2014 at 2:27 AM, Will Deacon <will.deacon@....com> wrote:
> On Wed, Sep 03, 2014 at 10:43:58PM +0100, Kees Cook wrote:
>> On Wed, Aug 20, 2014 at 5:28 AM, Kees Cook <keescook@...omium.org> wrote:
>> > On Tue, Aug 19, 2014 at 7:29 AM, Will Deacon <will.deacon@....com> wrote:
>> >> On Wed, Aug 13, 2014 at 06:06:29PM +0100, Kees Cook wrote:
>> >>> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
>> >>> +     __acquires(&patch_lock)
>> >>> +{
>> >>> +     unsigned int uintaddr = (uintptr_t) addr;
>> >>> +     bool module = !core_kernel_text(uintaddr);
>> >>> +     struct page *page;
>> >>> +
>> >>> +     if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
>> >>> +             page = vmalloc_to_page(addr);
>> >>> +     else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
>> >>> +             page = virt_to_page(addr);
>> >>> +     else
>> >>> +             return addr;
>> >>> +
>> >>> +     if (flags)
>> >>> +             spin_lock_irqsave(&patch_lock, *flags);
>> >>> +     else
>> >>> +             __acquire(&patch_lock);
>> >>
>> >> I don't understand the locking here. Why is it conditional, why do we need
>> >> to disable interrupts, and are you just racing against yourself?
>> >
>> > AIUI, the locking is here to avoid multiple users of the text poking
>> > fixmaps. It's conditional because there are two fixmaps
>> > (FIX_TEXT_POKE0 and FIX_TEXT_POKE1). Locking happens around 0 so
>> > locking around 1 is not needed since it is only ever used when 0 is in
>> > use. (__patch_text_real locks patch_lock before setting 0 when it uses
>> > remapping, and if it also needs 1, it doesn't have to lock since the
>> > lock is already held.)
>> >
>> >>> +     set_fixmap(fixmap, page_to_phys(page));
>> >>
>> >> set_fixmap does TLB invalidation, right? I think that means it can block on
>> >> 11MPCore and A15 w/ the TLBI erratum, so it's not safe to call this with
>> >> interrupts disabled anyway.
>> >
>> > Oh right. Hrm.
>> >
>> > In an earlier version of this series set_fixmap did not perform TLB
>> > invalidation. I wonder if this is not needed at all? (Wouldn't that be
>> > nice...)
>>
>> As suspected, my tests fail spectacularly without the TLB flush.
>> Adding WARN_ON(!irqs_disabled()) doesn't warn, so I think we're safe
>> here. Should I leave the WARN_ON in place for clarity, or some other
>> comments?
>
> I thought there was a potential call to spin_lock_irqsave right before
> this TLB flush?

I'm not sure I understand what you mean. Should I change something
here? It looks like irqs are disabled, so isn't this a safe code path?

-Kees

-- 
Kees Cook
Chrome OS Security
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/