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

Message ID CAKv+Gu93DcrAa65xGRF6rRtuq-Hjitk-B6RxV_9ztT=nKjQ_Ag@mail.gmail.com
State New
Headers show

Commit Message

Ard Biesheuvel Feb. 29, 2016, 12:39 p.m. UTC 
On 26 February 2016 at 17:57, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> 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@linaro.org>



FYI this results in a warning, please fold



> ---

>  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

>


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Patch

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 67ce440cb702..9cfe94b41b54 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -181,7 +181,7 @@  void __init arm64_memblock_init(void)
  * linear mapping. Take care not to clip the kernel which may be
  * high in memory.
  */
- memblock_remove(max(memstart_addr + linear_region_size, __pa(_end)),
+ memblock_remove(max_t(u64, memstart_addr + linear_region_size, __pa(_end)),
  ULLONG_MAX);
  if (memblock_end_of_DRAM() > linear_region_size)
  memblock_remove(0, memblock_end_of_DRAM() - linear_region_size);