Re: [PATCH] powerpc/32: Fix protection of kernel RAM after freeing unused memory

[Christophe LEROY]

Le 18/04/2017 à 08:40, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@xxxxxx> writes:
>
>
> > diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> > index a65c0b4c0669..d506bd61b629 100644
> > --- a/arch/powerpc/mm/pgtable_32.c
> > +++ b/arch/powerpc/mm/pgtable_32.c
> > @@ -323,6 +323,26 @@ get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep, pmd_t **pmdp)
> >          return(retval);
> >  }
> >
> > +void remap_init_ram(void)
> > +{
> > +	unsigned long start = (unsigned long)_sinittext & PAGE_MASK;
> > +	unsigned long end = (unsigned long)_einittext;
> > +	unsigned long va;
> > +
> > +	for (va = start; va < end; va += PAGE_SIZE) {
> > +		pte_t *kpte;
> > +		pmd_t *kpmd;
> > +		pte_t pte = pfn_pte(__pa(va) >> PAGE_SHIFT, PAGE_KERNEL);
> > +
> > +		if (!get_pteptr(&init_mm, va, &kpte, &kpmd))
> > +			continue;
> > +		__set_pte_at(&init_mm, va, kpte, pte, 0);
> > +		wmb();
> > +		pte_unmap(kpte);
> > +	}
> > +	flush_tlb_kernel_range(start, end);
> > +}
>
> Can we just use unmap_kernel_range() ?

We only want to remove the X bit.
I think unmap_kernel_range() will unmap the area, wheareas we want to 
keep it as part of the linear data area.

Christophe

> Is this sufficient on all 32-bit PPC? (I have no idea)
>
> cheers