[PATCH v2 2/2] arm64: mm: treat memstart_addr as a signed quantity

[Ard Biesheuvel]

Commit c031a4213c11 ("arm64: kaslr: randomize the linear region")
implements randomization of the linear region, by subtracting a random
multiple of PUD_SIZE from memstart_addr. This causes the virtual mapping
of system RAM to move upwards in the linear region, and at the same time
causes memstart_addr to assume a value which may be negative if the offset
of system RAM in the physical space is smaller than its offset relative to
PAGE_OFFSET in the virtual space.

Since memstart_addr is effectively an offset now, redefine its type as s64
so that expressions involving shifting or division preserve its sign.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 arch/arm64/include/asm/memory.h | 2 +-
 arch/arm64/mm/init.c            | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 5f8667a99e41..12f8a00fb3f1 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -135,7 +135,7 @@
 #include <linux/bitops.h>
 #include <linux/mmdebug.h>
 
-extern phys_addr_t		memstart_addr;
+extern s64			memstart_addr;
 /* PHYS_OFFSET - the physical address of the start of memory. */
 #define PHYS_OFFSET		({ VM_BUG_ON(memstart_addr & 1); memstart_addr; })
 
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 4ea7efc28e65..a2977d33e0dc 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -54,7 +54,7 @@
  * executes, which assigns it its actual value. So use a default value
  * that cannot be mistaken for a real physical address.
  */
-phys_addr_t memstart_addr __read_mostly = ~0ULL;
+s64 memstart_addr __read_mostly = -1;
 phys_addr_t arm64_dma_phys_limit __read_mostly;
 
 #ifdef CONFIG_BLK_DEV_INITRD
-- 
2.5.0