linux-kernel - Re: [PATCH v3 02/11] mm: Hardened usercopy

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Date:	Tue, 19 Jul 2016 15:55:54 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Laura Abbott <labbott@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Balbir Singh <bsingharora@...il.com>,
	Daniel Micay <danielmicay@...il.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
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	Casey Schaufler <casey@...aufler-ca.com>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Michael Ellerman <mpe@...erman.id.au>,
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	<linux-arm-kernel@...ts.infradead.org>, linux-ia64@...r.kernel.org,
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	<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v3 02/11] mm: Hardened usercopy

On Tue, Jul 19, 2016 at 12:12 PM, Kees Cook <keescook@...omium.org> wrote:
> On Mon, Jul 18, 2016 at 6:52 PM, Laura Abbott <labbott@...hat.com> wrote:
>> On 07/15/2016 02:44 PM, Kees Cook wrote:
>>> +static inline const char *check_heap_object(const void *ptr, unsigned
>>> long n,
>>> +                                           bool to_user)
>>> +{
>>> +       struct page *page, *endpage;
>>> +       const void *end = ptr + n - 1;
>>> +
>>> +       if (!virt_addr_valid(ptr))
>>> +               return NULL;
>>> +
>>
>>
>> virt_addr_valid returns true on vmalloc addresses on arm64 which causes some
>> intermittent false positives (tab completion in a qemu buildroot environment
>> was showing it fairly reliably). I think this is an arm64 bug because
>> virt_addr_valid should return true if and only if virt_to_page returns the
>> corresponding page. We can work around this for now by explicitly
>> checking against is_vmalloc_addr.
>
> Hrm, that's weird. Sounds like a bug too, but I'll add a check for
> is_vmalloc_addr() to catch it for now.

BTW, if you were testing against -next, KASAN moved things around in
copy_*_user() in a way I wasn't expecting (__copy* and copy* now both
call __arch_copy* instead of copy* calling __copy*). I'll have this
fixed in the next version.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security