Messages in this thread | | | Date | Wed, 4 Nov 2015 17:06:13 -0800 | Subject | Re: [PATCH] arm: Use kernel mm when updating section permissions | From | Kees Cook <> |
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On Wed, Nov 4, 2015 at 5:00 PM, Laura Abbott <labbott@fedoraproject.org> wrote: > Currently, read only permissions are not being applied even > when CONFIG_DEBUG_RODATA is set. This is because section_update > uses current->mm for adjusting the page tables. current->mm > need not be equivalent to the kernel version. Use pgd_offset_k > to get the proper page directory for updating. > > Signed-off-by: Laura Abbott <labbott@fedoraproject.org> > --- > I found this while trying to convince myself of something. > Dumping the page table via debugfs and writing to kernel text were both > showing the lack of mappings. This was observed on QEMU. Maybe it's just a > QEMUism but if not it probably should go to stable.
Well that's weird! debugfs showed the actual permissions that lacked RO? I wonder what changed. I tested this both with debugfs and lkdtm's KERN_WRITE test when the patches originally landed.
-Kees
> --- > arch/arm/mm/init.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c > index 8a63b4c..4bb936a 100644 > --- a/arch/arm/mm/init.c > +++ b/arch/arm/mm/init.c > @@ -629,11 +629,9 @@ static struct section_perm ro_perms[] = { > static inline void section_update(unsigned long addr, pmdval_t mask, > pmdval_t prot) > { > - struct mm_struct *mm; > pmd_t *pmd; > > - mm = current->active_mm; > - pmd = pmd_offset(pud_offset(pgd_offset(mm, addr), addr), addr); > + pmd = pmd_offset(pud_offset(pgd_offset_k(addr), addr), addr); > > #ifdef CONFIG_ARM_LPAE > pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot); > -- > 2.5.0 >
-- Kees Cook Chrome OS Security
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