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aaf4e1b05c
commit 295cf15623 upstream.
Al reminds us that the usercopy API must only return complete failure
if absolutely nothing could be copied. Currently, if userspace does
something silly like giving us an unaligned pointer to Device memory,
or a size which overruns MTE tag bounds, we may fail to honour that
requirement when faulting on a multi-byte access even though a smaller
access could have succeeded.
Add a mitigation to the fixup routines to fall back to a single-byte
copy if we faulted on a larger access before anything has been written
to the destination, to guarantee making *some* forward progress. We
needn't be too concerned about the overall performance since this should
only occur when callers are doing something a bit dodgy in the first
place. Particularly broken userspace might still be able to trick
generic_perform_write() into an infinite loop by targeting write() at
an mmap() of some read-only device register where the fault-in load
succeeds but any store synchronously aborts such that copy_to_user() is
genuinely unable to make progress, but, well, don't do that...
CC: stable@vger.kernel.org
Reported-by: Chen Huang <chenhuang5@huawei.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/dc03d5c675731a1f24a62417dba5429ad744234e.1626098433.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Huang <chenhuang5@huawei.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.