Re: [PATCH] MIPS: Always page align TASK_SIZE

[Harvey Hunt]

Hi David,

On 02/08/2016 10:11 AM, David Daney wrote:
> On 02/08/2016 10:05 AM, Harvey Hunt wrote:
> > STACK_TOP_MAX is aligned on a 32k boundary. When __bprm_mm_init()
> > creates an
> > initial stack for a process, it does so using STACK_TOP_MAX as the end
> > of the
> > vma. A process's arguments and environment information are placed on
> > the stack
> > and then the stack is relocated and aligned on a page boundary. When
> > using a 32
> > bit kernel with 64k pages, the relocated stack has the process's args
> > erroneously stored in the middle of the stack. This means that processes
> > receive no arguments or environment variables, preventing them from
> > running
> > correctly.
> >
> > Fix this by aligning TASK_SIZE on a page boundary.
> >
> > Signed-off-by: Harvey Hunt <harvey.hunt@xxxxxxxxxx>
> > Cc: David Daney <david.daney@xxxxxxxxxx>
> > Cc: Paul Burton <paul.burton@xxxxxxxxxx>
> > Cc: James Hogan <james.hogan@xxxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >   arch/mips/include/asm/processor.h | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/mips/include/asm/processor.h
> > b/arch/mips/include/asm/processor.h
> > index 3f832c3..b618b40 100644
> > --- a/arch/mips/include/asm/processor.h
> > +++ b/arch/mips/include/asm/processor.h
> > @@ -39,13 +39,13 @@ extern unsigned int vced_count, vcei_count;
> >   #ifdef CONFIG_32BIT
> >   #ifdef CONFIG_KVM_GUEST
> >   /* User space process size is limited to 1GB in KVM Guest Mode */
> > -#define TASK_SIZE    0x3fff8000UL
> > +#define TASK_SIZE    (0x40000000UL - PAGE_SIZE)
> >   #else
> >   /*
> >    * User space process size: 2GB. This is hardcoded into a few places,
> >    * so don't change it unless you know what you are doing.
> >    */
> > -#define TASK_SIZE    0x7fff8000UL
> > +#define TASK_SIZE    (0x7fff8000UL & PAGE_SIZE)
>
> Can you check your math here.  This doesn't seem correct.

Thanks for spotting that - it should have been:

(0x7fff8000UL & PAGE_MASK)

I'll do a v2 now.

> >   #endif
> >
> >   #define STACK_TOP_MAX    TASK_SIZE
> > @@ -62,7 +62,7 @@ extern unsigned int vced_count, vcei_count;
> >    * support 16TB; the architectural reserve for future expansion is
> >    * 8192EB ...
> >    */
> > -#define TASK_SIZE32    0x7fff8000UL
> > +#define TASK_SIZE32    (0x7fff8000UL & PAGE_SIZE)
>
> Same here.

As above.

> >   #define TASK_SIZE64    0x10000000000UL
> >   #define TASK_SIZE (test_thread_flag(TIF_32BIT_ADDR) ? TASK_SIZE32 :
> > TASK_SIZE64)
> >   #define STACK_TOP_MAX    TASK_SIZE64

Thanks,

Harvey