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linux/include/uapi
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Dan Williams 3234ac664a /dev/mem: Revoke mappings when a driver claims the region 
Close the hole of holding a mapping over kernel driver takeover event of
a given address range.

Commit 90a545e981 ("restrict /dev/mem to idle io memory ranges")
introduced CONFIG_IO_STRICT_DEVMEM with the goal of protecting the
kernel against scenarios where a /dev/mem user tramples memory that a
kernel driver owns. However, this protection only prevents *new* read(),
write() and mmap() requests. Established mappings prior to the driver
calling request_mem_region() are left alone.

Especially with persistent memory, and the core kernel metadata that is
stored there, there are plentiful scenarios for a /dev/mem user to
violate the expectations of the driver and cause amplified damage.

Teach request_mem_region() to find and shoot down active /dev/mem
mappings that it believes it has successfully claimed for the exclusive
use of the driver. Effectively a driver call to request_mem_region()
becomes a hole-punch on the /dev/mem device.

The typical usage of unmap_mapping_range() is part of
truncate_pagecache() to punch a hole in a file, but in this case the
implementation is only doing the "first half" of a hole punch. Namely it
is just evacuating current established mappings of the "hole", and it
relies on the fact that /dev/mem establishes mappings in terms of
absolute physical address offsets. Once existing mmap users are
invalidated they can attempt to re-establish the mapping, or attempt to
continue issuing read(2) / write(2) to the invalidated extent, but they
will then be subject to the CONFIG_IO_STRICT_DEVMEM checking that can
block those subsequent accesses.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: 90a545e981 ("restrict /dev/mem to idle io memory ranges")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/159009507306.847224.8502634072429766747.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2020-05-27 11:10:05 +02:00
..
asm-generic y2038: hide timeval/timespec/itimerval/itimerspec types 2020-02-21 11:22:15 -08:00
drm drm/amdgpu: add tiling flags from Mesa 2020-04-28 15:29:27 -04:00
linux /dev/mem: Revoke mappings when a driver claims the region 2020-05-27 11:10:05 +02:00
misc uapi: habanalabs: add gaudi defines 2020-05-19 14:48:41 +03:00
mtd mtd: abi: do not use C++ style comments in uapi header 2019-07-07 20:31:29 +02:00
rdma Merge branch 'mlx5_tx_steering' into rdma.git for-next 2020-03-27 13:26:59 -03:00
scsi uapi: revert flexible-array conversions 2020-05-04 11:30:15 -05:00
sound Revert "ALSA: uapi: Drop asound.h inclusion from asoc.h" 2020-03-31 11:01:12 +02:00
video License cleanup: add SPDX license identifier to uapi header files with a license 2017-11-02 11:20:11 +01:00
xen xen/gntdev: Add initial support for dma-buf UAPI 2018-07-26 23:05:14 -04:00
Kbuild kbuild: re-implement Makefile.headersinst without recursion 2019-06-15 19:57:02 +09:00