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

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

[Masahiro Yamada]

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 <yamada.m@jp.panasonic.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
---

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

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

[Ard Biesheuvel]

On 22 December 2014 at 04:17, Masahiro Yamada <yamada.m@jp.panasonic.com> 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 <yamada.m@jp.panasonic.com>
> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>


> ---
>
> 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
>

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

[Masahiro Yamada]

Hello Russell King,

Could you apply this patch for arm_add_memory() fix, please ?


Thanks,
Masahiro Yamada


On Mon, 22 Dec 2014 10:09:32 +0100
Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:

> On 22 December 2014 at 04:17, Masahiro Yamada <yamada.m@jp.panasonic.com> 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 <yamada.m@jp.panasonic.com>
> > Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
> 
> Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> 
> 
> > ---
> >
> > 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
> >
> 
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