From: John Hubbard <jhubbard@nvidia.com>
To: Jan Kara <jack@suse.cz>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
"Björn Töpel" <bjorn.topel@intel.com>,
"Christoph Hellwig" <hch@infradead.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Daniel Vetter" <daniel@ffwll.ch>,
"Dave Chinner" <david@fromorbit.com>,
"David Airlie" <airlied@linux.ie>,
"David S . Miller" <davem@davemloft.net>,
"Ira Weiny" <ira.weiny@intel.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>, "Jens Axboe" <axboe@kernel.dk>,
"Jonathan Corbet" <corbet@lwn.net>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Magnus Karlsson" <magnus.karlsson@intel.com>,
"Mauro Carvalho Chehab" <mchehab@kernel.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Paul Mackerras" <paulus@samba.org>,
"Shuah Khan" <shuah@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
bpf@vger.kernel.org, dri-devel@lists.freedesktop.org,
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LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v8 24/26] mm/gup: track FOLL_PIN pages
Date: Tue, 10 Dec 2019 16:27:02 -0800 [thread overview]
Message-ID: <918e9f4b-d1bc-95b4-3768-f6a28d625d58@nvidia.com> (raw)
In-Reply-To: <20191210133932.GH1551@quack2.suse.cz>
On 12/10/19 5:39 AM, Jan Kara wrote:
...
>> +void grab_page(struct page *page, unsigned int flags)
>> +{
>> + if (flags & FOLL_GET)
>> + get_page(page);
>> + else if (flags & FOLL_PIN) {
>> + get_page(page);
>> + WARN_ON_ONCE(flags & FOLL_GET);
>> + /*
>> + * Use get_page(), above, to do the refcount error
>> + * checking. Then just add in the remaining references:
>> + */
>> + page_ref_add(page, GUP_PIN_COUNTING_BIAS - 1);
>
> This is wrong for two reasons:
>
> 1) You miss compound_head() indirection from get_page() for this
> page_ref_add().
whoops, yes that is missing.
>
> 2) page_ref_add() could overflow the counter without noticing.
>
> Especially with GUP_PIN_COUNTING_BIAS being non-trivial, it is realistic
> that an attacker might try to overflow the page refcount and we have to
> protect the kernel against that. So I think that all the places that would
> use grab_page() actually need to use try_grab_page() and then gracefully
> deal with the failure.
>
OK, I've replaced grab_page() everywhere with try_grab_page(), with the
above issues fixed. The v7 patchset had error handling for grab_page() failures,
that had been reviewed, so relevants parts of that have reappeared.
I had initially hesitated to do this, but now I've gone ahead and added:
#define page_ref_zero_or_close_to_bias_overflow(page) \
((unsigned int) page_ref_count(page) + \
GUP_PIN_COUNTING_BIAS <= GUP_PIN_COUNTING_BIAS)
...which is used in the new try_grab_page() for protection.
>> @@ -278,11 +425,23 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
>> goto retry;
>> }
>>
>> - if (flags & FOLL_GET) {
>> + if (flags & (FOLL_PIN | FOLL_GET)) {
>> + /*
>> + * Allow try_get_page() to take care of error handling, for
>> + * both cases: FOLL_GET or FOLL_PIN:
>> + */
>> if (unlikely(!try_get_page(page))) {
>> page = ERR_PTR(-ENOMEM);
>> goto out;
>> }
>> +
>> + if (flags & FOLL_PIN) {
>> + WARN_ON_ONCE(flags & FOLL_GET);
>> +
>> + /* We got a +1 refcount from try_get_page(), above. */
>> + page_ref_add(page, GUP_PIN_COUNTING_BIAS - 1);
>> + __update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, 1);
>> + }
>> }
>
> The same problem here as above, plus this place should use the same
> try_grab..() helper, shouldn't it?
Yes, now that the new try_grab_page() has behavior that matches what
this call site needs. Done.
>
>> @@ -544,8 +703,8 @@ static struct page *follow_page_mask(struct vm_area_struct *vma,
>> /* make this handle hugepd */
>> page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
>> if (!IS_ERR(page)) {
>> - BUG_ON(flags & FOLL_GET);
>> - return page;
>> + WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN));
>> + return NULL;
>
> I agree with the change to WARN_ON_ONCE but why is correct the change of
> the return value? Note that this is actually a "success branch".
>
Good catch, thanks! I worked through the logic...correctly at first, but then I must
have become temporarily dazed by the raw destructive power of the pre-existing
BUG_ON() statement, and screwed it up after all. :)
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2019-12-11 0:27 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-09 22:53 [PATCH v8 00/26] mm/gup: track dma-pinned pages: FOLL_PIN John Hubbard
2019-12-09 22:53 ` [PATCH v8 01/26] mm/gup: factor out duplicate code from four routines John Hubbard
2019-12-09 22:53 ` [PATCH v8 02/26] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-12-09 22:53 ` [PATCH v8 03/26] mm: Cleanup __put_devmap_managed_page() vs ->page_free() John Hubbard
2019-12-09 22:53 ` [PATCH v8 04/26] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-12-09 22:53 ` [PATCH v8 05/26] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-12-09 22:53 ` [PATCH v8 06/26] mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM John Hubbard
2019-12-09 22:53 ` [PATCH v8 07/26] vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call John Hubbard
2019-12-09 22:53 ` [PATCH v8 08/26] mm/gup: allow FOLL_FORCE for get_user_pages_fast() John Hubbard
2019-12-10 10:28 ` Jan Kara
2019-12-09 22:53 ` [PATCH v8 09/26] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-12-09 22:53 ` [PATCH v8 10/26] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-12-09 22:53 ` [PATCH v8 11/26] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-12-09 22:53 ` [PATCH v8 12/26] IB/{core,hw,umem}: set FOLL_PIN via pin_user_pages*(), fix up ODP John Hubbard
2019-12-09 22:53 ` [PATCH v8 13/26] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-12-09 22:53 ` [PATCH v8 14/26] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-12-09 22:53 ` [PATCH v8 15/26] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-12-09 22:53 ` [PATCH v8 16/26] net/xdp: " John Hubbard
2019-12-09 22:53 ` [PATCH v8 17/26] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-12-10 0:56 ` Andrew Morton
2019-12-10 5:48 ` John Hubbard
2019-12-10 10:17 ` Jan Kara
2019-12-09 22:53 ` [PATCH v8 18/26] media/v4l2-core: pin_user_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-12-09 22:53 ` [PATCH v8 19/26] vfio, mm: " John Hubbard
2019-12-09 22:53 ` [PATCH v8 20/26] powerpc: book3s64: convert to pin_user_pages() and put_user_page() John Hubbard
2019-12-09 23:46 ` John Hubbard
2019-12-10 5:53 ` John Hubbard
2019-12-11 0:49 ` Andrew Morton
2019-12-09 22:53 ` [PATCH v8 21/26] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-12-09 22:53 ` [PATCH v8 22/26] mm, tree-wide: rename put_user_page*() to unpin_user_page*() John Hubbard
2019-12-09 22:53 ` [PATCH v8 23/26] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-12-10 12:49 ` Jan Kara
2019-12-11 0:27 ` John Hubbard
2019-12-09 22:53 ` [PATCH v8 24/26] mm/gup: track FOLL_PIN pages John Hubbard
2019-12-10 13:39 ` Jan Kara
2019-12-11 0:27 ` John Hubbard [this message]
2019-12-09 22:53 ` [PATCH v8 25/26] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-12-09 22:53 ` [PATCH v8 26/26] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
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