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Date: Mon, 12 Mar 2018 23:25:54 +0200
From: Igor Stoppa <igor.stoppa@...wei.com>
To: Matthew Wilcox <willy@...radead.org>
CC: <david@...morbit.com>, <keescook@...omium.org>, <mhocko@...nel.org>,
<labbott@...hat.com>, <linux-security-module@...r.kernel.org>,
<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 4/7] Protectable Memory
On 12/03/18 21:13, Matthew Wilcox wrote:
> On Wed, Feb 28, 2018 at 10:06:17PM +0200, Igor Stoppa wrote:
>> struct gen_pool *pmalloc_create_pool(const char *name,
>> int min_alloc_order);
>> int is_pmalloc_object(const void *ptr, const unsigned long n);
>> bool pmalloc_prealloc(struct gen_pool *pool, size_t size);
>> void *pmalloc(struct gen_pool *pool, size_t size, gfp_t gfp);
>> static inline void *pzalloc(struct gen_pool *pool, size_t size, gfp_t gfp)
>> static inline void *pmalloc_array(struct gen_pool *pool, size_t n,
>> size_t size, gfp_t flags)
>> static inline void *pcalloc(struct gen_pool *pool, size_t n,
>> size_t size, gfp_t flags)
>> static inline char *pstrdup(struct gen_pool *pool, const char *s, gfp_t gfp)
>> int pmalloc_protect_pool(struct gen_pool *pool);
>> static inline void pfree(struct gen_pool *pool, const void *addr)
>> int pmalloc_destroy_pool(struct gen_pool *pool);
>
> Do you have users for all these functions? I'm particularly sceptical of
> pfree().
The typical case is when rolling back allocations, on an error path.
For example, with SELinux, the userspace provides the policy, which gets
processed and converted into a policyDB, where every policy maps to
several structures allocated dynamically.
The allocation is not transactional. In case a policy turns out to be
bad/broken, while being interpreted, those structures that were
initially allocated for that policy, must be freed.
Since pmalloc is meant to be a drop in replacement for k/vmalloc, it
needs to provide also pfree.
> To my mind, a user wants to:
>
> pmalloc_create();
> pmalloc(); * N
> pmalloc_protect();
> ...
> pmalloc_destroy();
This is the simplest case, but also the error path must be supported.
> I don't mind the pstrdup, pcalloc, pmalloc_array, pzalloc variations, but
All those functions turned out to be necessary when converting SELinux
to pmalloc.
Yes, I haven't published this code yet, but I was hoping to first be
done with pmalloc and then move on to SELinux, which I suspect will be
harder to chew :-/
> I don't know why you need is_pmalloc_object().
Because of hardened usercopy [1]:
On 23/05/17 00:38, Kees Cook wrote:
[...]
> I'd like hardened usercopy to grow knowledge of these
> allocations so we can bounds-check objects. Right now, mm/usercopy.c
> just looks at PageSlab(page) to decide if it should do slab checks. I
> think adding a check for this type of object would be very important
> there.
[1] http://www.openwall.com/lists/kernel-hardening/2017/05/23/17
--
igor
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