linux-kernel - Re: [PATCH v6 2/4] x86/modules: Increase randomization for modules

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Date:   Mon, 24 Sep 2018 12:58:51 -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 2/4] x86/modules: Increase randomization for modules

On Mon, Sep 24, 2018 at 11:57 AM, Edgecombe, Rick P
<rick.p.edgecombe@...el.com> wrote:
> On Fri, 2018-09-21 at 12:05 -0700, Kees Cook wrote:
>> On Thu, Sep 13, 2018 at 2:31 PM, Rick Edgecombe
>> <rick.p.edgecombe@...el.com> wrote:
>> I would find this much more readable as:
>> static unsigned long get_module_vmalloc_start(void)
>> {
>>        unsigned long addr = MODULES_VADDR;
>>
>>        if (kaslr_randomize_base())
>>               addr += get_module_load_offset();
>>
>>        if (kaslr_randomize_each_module())
>>                addr += get_modules_rand_len();
>>
>>        return addr;
>> }
> Thanks, that looks better.
>
>>
>> >  void *module_alloc(unsigned long size)
>> >  {
>> > @@ -84,16 +201,18 @@ void *module_alloc(unsigned long size)
>> >         if (PAGE_ALIGN(size) > MODULES_LEN)
>> >                 return NULL;
>> >
>> > -       p = __vmalloc_node_range(size, MODULE_ALIGN,
>> > -                                   MODULES_VADDR +
>> > get_module_load_offset(),
>> > -                                   MODULES_END, GFP_KERNEL,
>> > -                                   PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
>> > -                                   __builtin_return_address(0));
>> > +       p = try_module_randomize_each(size);
>> > +
>> > +       if (!p)
>> > +               p = __vmalloc_node_range(size, MODULE_ALIGN,
>> > +                               get_module_vmalloc_start(), MODULES_END,
>> > +                               GFP_KERNEL, PAGE_KERNEL_EXEC, 0,
>> > +                               NUMA_NO_NODE, __builtin_return_address(0));
>> Instead of having two open-coded __vmalloc_node_range() calls left in
>> this after the change, can this be done in terms of a call to
>> try_module_alloc() instead? I see they're slightly different, but it
>> might be nice for making the two paths share more code.
> Not sure what you mean. Across the whole change, there is one call
> to __vmalloc_node_range, and one to __vmalloc_node_try_addr.

I guess I meant the vmalloc calls -- one for node_range and one for
node_try_addr. I was wondering if the logic could be combined in some
way so that the __vmalloc_node_range() could be made in terms of the
the helper that try_module_randomize_each() uses. But this could just
be me hoping for nice-to-read changes. ;)

-Kees

-- 
Kees Cook
Pixel Security