Messages in this thread | | | Subject | Re: [RFC PATCH v16 0/6] mm: security: ro protection for dynamic data | From | Igor Stoppa <> | Date | Tue, 20 Feb 2018 20:03:49 +0200 |
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On 20/02/18 03:21, Dave Chinner wrote: > On Mon, Feb 12, 2018 at 03:32:36PM -0800, Kees Cook wrote: >> On Mon, Feb 12, 2018 at 8:52 AM, Igor Stoppa <igor.stoppa@huawei.com> wrote: >>> This patch-set introduces the possibility of protecting memory that has >>> been allocated dynamically. >>> >>> The memory is managed in pools: when a memory pool is turned into R/O, >>> all the memory that is part of it, will become R/O. >>> >>> A R/O pool can be destroyed, to recover its memory, but it cannot be >>> turned back into R/W mode. >>> >>> This is intentional. This feature is meant for data that doesn't need >>> further modifications after initialization. >> >> This series came up in discussions with Dave Chinner (and Matthew >> Wilcox, already part of the discussion, and others) at LCA. I wonder >> if XFS would make a good initial user of this, as it could allocate >> all the function pointers and other const information about a >> superblock in pmalloc(), keeping it separate from the R/W portions? >> Could other filesystems do similar things? > > I wasn't cc'd on this patchset, (please use david@fromorbit.com for > future postings)
Apologies, somehow I didn't realize that I should have put you too in CC. It will be fixed at the next iteration.
> so I can't really say anything about it right > now. My interest for XFS was that we have a fair amount of static > data in XFS that we set up at mount time and it never gets modified > after that.
This is the typical use case I had in mind, although it requires a conversion. Ex:
before:
static int a;
void set_a(void) { a = 4; }
after:
static int *a __ro_after_init; struct gen_pool *pool;
void init_a(void) { pool = pmalloc_create_pool("pool", 0); a = (int *)pmalloc(pool, sizeof(int), GFP_KERNEL); }
void set_a(void) { *a = 4; pmalloc_protect_pool(pool); }
> I'm not so worried about VFS level objects (that's a > much more complex issue) but there is a lot of low hanging fruit in > the XFS structures we could convert to write-once structures.
I'd be interested to have your review of the pmalloc API, if you think something is missing, once I send out the next revision.
-- igor
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