Re: [PATCH v6 11/14] mips: Adjust brk randomization offset to fit generic version

[Alexandre Ghiti]

On 8/8/19 11:19 AM, Sergei Shtylyov wrote:
> Hello!
>
> On 08.08.2019 9:17, Alexandre Ghiti wrote:
>
> > This commit simply bumps up to 32MB and 1GB the random offset
> > of brk, compared to 8MB and 256MB, for 32bit and 64bit respectively.
> >
> > Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> > Acked-by: Paul Burton <paul.burton@xxxxxxxx>
> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> > ---
> > Â arch/mips/mm/mmap.c | 7 ++++---
> > Â 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> > index a7e84b2e71d7..ff6ab87e9c56 100644
> > --- a/arch/mips/mm/mmap.c
> > +++ b/arch/mips/mm/mmap.c
> [...]
> > @@ -189,11 +190,11 @@ static inline unsigned long brk_rnd(void)
> > ÂÂÂÂÂ unsigned long rnd = get_random_long();
> > Â ÂÂÂÂÂ rnd = rnd << PAGE_SHIFT;
> > -ÂÂÂ /* 8MB for 32bit, 256MB for 64bit */
> > +ÂÂÂ /* 32MB for 32bit, 1GB for 64bit */
> > ÂÂÂÂÂ if (TASK_IS_32BIT_ADDR)
> > -ÂÂÂÂÂÂÂ rnd = rnd & 0x7ffffful;
> > +ÂÂÂÂÂÂÂ rnd = rnd & (SZ_32M - 1);
> > ÂÂÂÂÂ else
> > -ÂÂÂÂÂÂÂ rnd = rnd & 0xffffffful;
> > +ÂÂÂÂÂÂÂ rnd = rnd & (SZ_1G - 1);
>
> ÂÂ Why not make these 'rnd &= SZ_* - 1', while at it anyways?


You're right, I could have. Again, this code gets removed afterwards, so 
I think it's ok
to leave it as is.

Anyway, thanks for your remarks Sergei !

Alex


> [...]
>
> MBR, Sergei
>
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