commit b34e7e298d7a5ed76b3aa327c240c29f1ef6dd22 upstream.
WRITE_ONCE() isn't the correct way to publish a pointer to a data
structure, since it doesn't include a write memory barrier. Therefore
other tasks may see that the pointer has been set but not see that the
pointed-to memory has finished being initialized yet. Instead a
primitive with "release" semantics is needed.
Use smp_store_release() for this.
The use of READ_ONCE() on the read side is still potentially correct if
there's no control dependency, i.e. if all memory being "published" is
transitively reachable via the pointer itself. But this pairing is
somewhat confusing and error-prone. So just upgrade the read side to
smp_load_acquire() so that it clearly pairs with smp_store_release().
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>
Fixes: 3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims the region")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: stable <stable@vger.kernel.org>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/20200716060553.24618-1-ebiggers@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ Upstream commit 3234ac664a870e6ea69ae3a57d824cd7edbeacc5 ]
Close the hole of holding a mapping over kernel driver takeover event of
a given address range.
Commit 90a545e98126 ("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: 90a545e98126 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Eric Biggers