From: Laura Abbott <labbott@redhat.com>
To: Liam Mark <lmark@codeaurora.org>, Sumit Semwal <sumit.semwal@linaro.org>
Cc: devel@driverdev.osuosl.org, "Todd Kjos" <tkjos@android.com>,
linux-kernel@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
"Arve Hjønnevåg" <arve@android.com>,
"Martijn Coenen" <maco@android.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC] android: ion: How to properly clean caches for uncached allocations
Date: Wed, 7 Mar 2018 15:15:01 -0800 [thread overview]
Message-ID: <b1479541-13bd-85ea-f9c7-25264c91f9b9@redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.02.1802282111320.22860@lmark-linux.qualcomm.com>
On 02/28/2018 09:18 PM, Liam Mark wrote:
> The issue:
>
> Currently in ION if you allocate uncached memory it is possible that there
> are still dirty lines in the cache. And often these dirty lines in the
> cache are the zeros which were meant to clear out any sensitive kernel
> data.
>
> What this means is that if you allocate uncached memory from ION, and then
> subsequently write to that buffer (using the uncached mapping you are
> provided by ION) then the data you have written could be corrupted at some
> point in the future if a dirty line is evicted from the cache.
>
> Also this means there is a potential security issue. If an un-privileged
> userspace user allocated uncached memory (for example from the system heap)
> and then if they were to read from that buffer (through the un-cached
> mapping they are provided by ION), and if some of the zeros which were
> written to that memory are still in the cache then this un-privileged
> userspace user could read potentially sensitive kernel data.
For the use case you are describing we don't actually need the
memory to be non-cached until it comes time to do the dma mapping.
Here's a proposal to shoot holes in:
- Before any dma_buf attach happens, all mmap mappings are cached
- At the time attach happens, we shoot down any existing userspace
mappings, do the dma_map with appropriate flags to clean the pages
and then allow remapping to userspace as uncached. Really this
looks like a variation on the old Ion faulting code which I removed
except it's for uncached buffers instead of cached buffers.
Potential problems:
- I'm not 100% about the behavior here if the attaching device
is already dma_coherent. I also consider uncached mappings
enough of a device specific optimization that you shouldn't
do them unless you know it's needed.
- The locking/sequencing with userspace could be tricky
since userspace may not like us ripping mappings out from
underneath if it's trying to access.
Thoughts?
Thanks,
Laura
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next prev parent reply other threads:[~2018-03-07 23:15 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-01 5:18 [RFC] android: ion: How to properly clean caches for uncached allocations Liam Mark
2018-03-07 23:15 ` Laura Abbott [this message]
2018-03-09 0:45 ` Liam Mark
2018-03-09 2:01 ` Laura Abbott
2018-11-01 22:15 ` [RFC PATCH v2] " Liam Mark
2018-11-02 19:01 ` John Stultz
2018-11-06 21:20 ` Liam Mark
2018-11-20 16:46 ` Brian Starkey
2018-11-27 4:59 ` Liam Mark
2018-11-27 10:35 ` Brian Starkey
2018-11-28 6:46 ` Liam Mark
2018-11-28 11:10 ` Brian Starkey
2018-11-29 7:03 ` Liam Mark
2018-11-29 14:14 ` Brian Starkey
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