2014-12-22 03:19:17

by Masahiro Yamada

Subject: [PATCH v2] ARM: mm: fix size rounding-down of arm_add_memory() function

The current rounding of "size" is wrong:

- If "start" is sufficiently near the next page boundary, "size"
is decremented by more than enough and the last page is lost.

- If "size" is sufficiently small, it is wrapped around and gets
a bogus value.

Signed-off-by: Masahiro Yamada <[email protected]>
Acked-by: Geert Uytterhoeven <[email protected]>
---

Changes in v2:
- Avoid wrap around of "size"

arch/arm/kernel/setup.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index f9c8639..d13f185 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -657,10 +657,13 @@ int __init arm_add_memory(u64 start, u64 size)

/*
* Ensure that start/size are aligned to a page boundary.
- * Size is appropriately rounded down, start is rounded up.
+ * Size is rounded down, start is rounded up.
*/
- size -= start & ~PAGE_MASK;
aligned_start = PAGE_ALIGN(start);
+ if (aligned_start > start + size)
+ size = 0;
+ else
+ size -= aligned_start - start;

#ifndef CONFIG_ARCH_PHYS_ADDR_T_64BIT
if (aligned_start > ULONG_MAX) {
--
1.9.1

2014-12-22 09:09:35

by Ard Biesheuvel

Subject: Re: [PATCH v2] ARM: mm: fix size rounding-down of arm_add_memory() function

On 22 December 2014 at 04:17, Masahiro Yamada <[email protected]> wrote:
> The current rounding of "size" is wrong:
>
> - If "start" is sufficiently near the next page boundary, "size"
> is decremented by more than enough and the last page is lost.
>
> - If "size" is sufficiently small, it is wrapped around and gets
> a bogus value.
>
> Signed-off-by: Masahiro Yamada <[email protected]>
> Acked-by: Geert Uytterhoeven <[email protected]>

Acked-by: Ard Biesheuvel <[email protected]>


> ---
>
> Changes in v2:
> - Avoid wrap around of "size"
>
> arch/arm/kernel/setup.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index f9c8639..d13f185 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -657,10 +657,13 @@ int __init arm_add_memory(u64 start, u64 size)
>
> /*
> * Ensure that start/size are aligned to a page boundary.
> - * Size is appropriately rounded down, start is rounded up.
> + * Size is rounded down, start is rounded up.
> */
> - size -= start & ~PAGE_MASK;
> aligned_start = PAGE_ALIGN(start);
> + if (aligned_start > start + size)
> + size = 0;
> + else
> + size -= aligned_start - start;
>
> #ifndef CONFIG_ARCH_PHYS_ADDR_T_64BIT
> if (aligned_start > ULONG_MAX) {
> --
> 1.9.1
>