Commit f4189029 authored Mar 02, 2016 by Ard Biesheuvel Committed by Jeff Vander Stoep Sep 22, 2016

UPSTREAM: arm64: mm: check at build time that PAGE_OFFSET divides the VA space evenly



Commit 8439e62a1561 ("arm64: mm: use bit ops rather than arithmetic in
pa/va translations") changed the boundary check against PAGE_OFFSET from
an arithmetic comparison to a bit test. This means we now silently assume
that PAGE_OFFSET is a power of 2 that divides the kernel virtual address
space into two equal halves. So make that assumption explicit.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Bug: 30369029
Patchset: kaslr-arm64-4.4

(cherry picked from commit 6d2aa549de1fc998581d216de3853aa131aa4446)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: I8c3bc8cdb7d7f7dea092fd1a208b04583a141054

parent 1c4143d4

arch/arm64/mm/init.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -172,6 +172,13 @@ void __init arm64_memblock_init(void)
		{
		const s64 linear_region_size = -(s64)PAGE_OFFSET;

		/*
		* Ensure that the linear region takes up exactly half of the kernel
		* virtual address space. This way, we can distinguish a linear address
		* from a kernel/module/vmalloc address by testing a single bit.
		*/
		BUILD_BUG_ON(linear_region_size != BIT(VA_BITS - 1));

		/*
		* Select a suitable value for the base of physical memory.
		*/