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Message-ID: <b83b980d-8adb-52ea-9b62-af33aff8f898@huawei.com>
Date: Wed, 9 Aug 2017 10:27:32 +0300
From: Igor Stoppa <igor.stoppa@...wei.com>
To: Jerome Glisse <jglisse@...hat.com>
CC: Michal Hocko <mhocko@...nel.org>, Linux-MM <linux-mm@...ck.org>,
LKML
<linux-kernel@...r.kernel.org>,
<linux-security-module@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Kees Cook <keescook@...gle.com>
Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc
allocator
On 09/08/17 02:15, Jerome Glisse wrote:
> On Tue, Aug 08, 2017 at 03:59:36PM +0300, Igor Stoppa wrote:
[...]
>> I am tempted to add
>>
>> #define VM_PMALLOC 0x00000100
[...]
> VM_PMALLOC sounds fine to me also adding a comment there pointing to
> pmalloc documentation would be a good thing to do. The above are flags
> that are use only inside vmalloc context and so there is no issue
> here of conflicting with other potential user.
ok, will do
>>
>> Unless it's acceptable to check the private field in the page struct.
>> It would bear the pmalloc magic number.
>
> I thought you wanted to do:
> check struct page mapping field
> check vmap->flags for VM_PMALLOC
>
> bool is_pmalloc(unsigned long addr)
> {
> struct page *page;
> struct vm_struct *vm_struct;
>
> if (!is_vmalloc_addr(addr))
> return false;
> page = vmalloc_to_page(addr);
> if (!page)
> return false;
> if (page->mapping != pmalloc_magic_key)
page->private ?
I thought mapping would not work in the cases you mentioned?
> return false;
>
> vm_struct = find_vm_area(addr);
> if (!vm_struct)
> return false;
>
> return vm_struct->flags & VM_PMALLOC;
> }
>
> Did you change your plan ?
No, the code I have is almost 1:1 what you wrote.
Apart from mapping <=> private
In my previous mail I referred to page->private.
Maybe I was not very clear in what I wrote, but I'm almost 100% aligned
with your snippet.
>> I'm thinking to use a pointer to one of pmalloc data items, as signature.
>
> What ever is easier for you. Note that dereferencing such pointer before
> asserting this is really a pmalloc page would be hazardous.
Yes, it's not even needed in this scenario.
It was just a way to ensure that it would be a value that cannot be come
out accidentally as pointer value, since it is already taken.
--
igor
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