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Message-ID: <a9c0b60b-d540-785b-3455-d35ae051b891@huawei.com>
Date: Tue, 6 Jun 2017 15:23:12 +0300
From: Igor Stoppa <igor.stoppa@...wei.com>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
CC: <keescook@...omium.org>, <mhocko@...nel.org>, <jmorris@...ei.org>,
<paul@...l-moore.com>, <sds@...ho.nsa.gov>, <casey@...aufler-ca.com>,
<hch@...radead.org>, <labbott@...hat.com>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>, <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 2/5] Protectable Memory Allocator
On 06/06/17 15:08, Tetsuo Handa wrote:
> Igor Stoppa wrote:
>>>> +struct pmalloc_node {
>>>> + struct hlist_node nodes_list;
>>>> + atomic_t used_words;
>>>> + unsigned int total_words;
>>>> + __PMALLOC_ALIGNED align_t data[];
>>>> +};
>>>
>>> Is this __PMALLOC_ALIGNED needed? Why not use "long" and "BITS_PER_LONG" ?
>>
>> In an earlier version I actually asked the same question.
>> It is currently there because I just don't know enough about various
>> architectures. The idea of having "align_t" was that it could be tied
>> into what is the most desirable alignment for each architecture.
>> But I'm actually looking for advise on this.
>
> I think that let the compiler use natural alignment is OK.
On a 64 bit machine the preferred alignment might be either 32 or 64,
depending on the application. How can the compiler choose?
>>> You need to check for node != NULL before dereference it.
>>
>> So, if I understood correctly, there shouldn't be a case where node is
>> NULL, right?
>> Unless it has been tampered/damaged. Is that what you mean?
>
> I meant to say
>
> + node = __pmalloc_create_node(req_words);
> // this location.
> + starting_word = atomic_fetch_add(req_words, &node->used_words);
argh, yes
>>>> +const char *__pmalloc_check_object(const void *ptr, unsigned long n)
>>>> +{
>>>> + unsigned long p;
>>>> +
>>>> + p = (unsigned long)ptr;
>>>> + n += (unsigned long)ptr;
>>>> + for (; (PAGE_MASK & p) <= (PAGE_MASK & n); p += PAGE_SIZE) {
>>>> + if (is_vmalloc_addr((void *)p)) {
>>>> + struct page *page;
>>>> +
>>>> + page = vmalloc_to_page((void *)p);
>>>> + if (!(page && PagePmalloc(page)))
>>>> + return msg;
>>>> + }
>>>> + }
>>>> + return NULL;
>>>> +}
>>>
>>> I feel that n is off-by-one if (ptr + n) % PAGE_SIZE == 0
>>> according to check_page_span().
>>
>> It seems to work. If I am missing your point, could you please
>> use the same format of the example I made, to explain me?
>
> If ptr == NULL and n == PAGE_SIZE so that (ptr + n) % PAGE_SIZE == 0,
> this loop will access two pages (one page containing p == 0 and another
> page containing p == PAGE_SIZE) when this loop should access only one
> page containing p == 0. When checking n bytes, it's range is 0 to n - 1.
oh, so:
p = (unsigned long) ptr;
n = p + n - 1;
--
igor
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