Re: [PATCH] MIPS: Always page align TASK_SIZE

[David Daney]

On 02/08/2016 01:48 PM, Harvey Hunt wrote:
> Hi Joshua,
>
> On 02/08/2016 01:35 PM, Joshua Kinard wrote:
> > On 02/08/2016 13:15, Harvey Hunt wrote:
> > > 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.
> >
> > FYI, TASK_SIZE was recently changed to 0x80000000UL in commit
> > 7f8ca9cb1ed3 on
> > the linux-mips.org tree.
>
> Thanks, I'll rebase.

You may find that in rebasing, suddenly you have a completely empty patch!


> > > > >    #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