tag 4ab698f2375c629116f493956c3adb4107919f5e
tagger Todd Kjos <tkjos@google.com> Tue Feb 02 13:31:53 2021 -0800
object 90935b28546d2cfb7541d76c71e749496f77968b

https://source.android.com/security/bulletin/2021-02-01
CVE-2017-18509
CVE-2020-10767

commit 90935b28546d2cfb7541d76c71e749496f77968b
author Hridya Valsaraju <hridya@google.com> Mon Feb 01 11:37:50 2021 -0800
committer Suren Baghdasaryan <surenb@google.com> Tue Feb 02 18:47:14 2021 +0000
tree 12eb688d5319d875bebd503c398c978d52bf4c59
parent 5ad6bc057fe4994cca48c48d46df9bbdc5ce9667

BACKPORT: FROMLIST: dmabuf: Add the capability to expose DMA-BUF stats in sysfs

This patch allows statistics to be enabled for each DMA-BUF in
sysfs by enabling the config CONFIG_DMABUF_SYSFS_STATS.

The following stats will be exposed by the interface:

/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
/sys/kernel/dmabuf/buffers/<inode_number>/size
/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device
/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter

The inode_number is unique for each DMA-BUF and was added earlier [1]
in order to allow userspace to track DMA-BUF usage across different
processes.

Currently, this information is exposed in
/sys/kernel/debug/dma_buf/bufinfo.
However, since debugfs is considered unsafe to be mounted in production,
it is being duplicated in sysfs.

This information will be used to derive DMA-BUF
per-exporter stats and per-device usage stats for Android Bug reports.
The corresponding userspace changes can be found at [2].
Telemetry tools will also capture this information(along with other
memory metrics) periodically as well as on important events like a
foreground app kill (which might have been triggered by Low Memory
Killer). It will also contribute to provide a snapshot of the system
memory usage on other events such as OOM kills and Application Not
Responding events.

A shell script that can be run on a classic Linux environment to read
out the DMA-BUF statistics can be found at [3](suggested by John
Stultz).

The patch contains the following improvements over the previous version:
1) Each attachment is represented by its own directory to allow creating
a symlink to the importing device and to also provide room for future
expansion.
2) The number of distinct mappings of each attachment is exposed in a
separate file.
3) The per-buffer statistics are now in /sys/kernel/dmabuf/buffers
inorder to make the interface expandable in future.

All of the improvements above are based on suggestions/feedback from
Daniel Vetter and Christian König.

[1]: https://lore.kernel.org/patchwork/patch/1088791/
[2]: https://android-review.googlesource.com/q/topic:%22dmabuf-sysfs%22+(status:open%20OR%20status:merged)
[3]: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1549734

Bug: 167709539
Link: https://lore.kernel.org/linux-media/20210126204240.418297-1-hridya@google.com/
[hridya: rebase needed in drivers/dma-buf/dma-buf.c for backporting]
[hridya: changed sysfs_emit to sprintf since its not available in 5.4]
Signed-off-by: Hridya Valsaraju <hridya@google.com>
Reported-by: kernel test robot <lkp@intel.com>
Change-Id: I8a3342b57f2e21ff349839f5cf665980c97bf849