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As a hardening measure, we currently randomize the placement of physical memory inside the linear region when KASLR is in effect. Since the random offset at which to place the available physical memory inside the linear region is chosen early at boot, it is based on the memblock description of memory, which does not cover hotplug memory. The consequence of this is that the randomization offset may be chosen such that any hotplugged memory located above memblock_end_of_DRAM() that appears later is pushed off the end of the linear region, where it cannot be accessed. So let's limit this randomization of the linear region to ensure that this can no longer happen, by using the CPU's addressable PA range instead. As it is guaranteed that no hotpluggable memory will appear that falls outside of that range, we can safely put this PA range sized window anywhere in the linear region. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Steven Price <steven.price@arm.com> Cc: Robin Murphy <robin.murphy@arm.com> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org Signed-off-by: Catalin Marinas <catalin.marinas@arm.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.
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.