On Thu, Nov 19, 2015 at 11:10 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Wed, Nov 18, 2015 at 4:14 PM, Laura Abbott <labbott@xxxxxxxxxxxxxxxxx> wrote:
>> Currently, when updating section permissions to mark areas RO
>> or NX, the only mm updated is current->mm. This is working off
>> the assumption that there are no additional mm structures at
>> the time. This may not always hold true. (Example: calling
>> modprobe early will trigger a fork/exec). Ensure all mm structres
>> get updated with the new section information.
>>
>> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
>
> This looks right to me. :)
>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
>
> Russell, does this work for you?
Did this end up in the patch tracker? (I just sent a patch that'll
collide with this... I'm happy to do the fix up.)
-Kees
>
> -Kees
>
>> ---
>> I don't think we can get away from updating the sections if the initmem is
>> going to be freed back to the buddy allocator. I think this should cover
>> everything based on my understanding but my knowledge may be incomplete.
>> ---
>> arch/arm/mm/init.c | 92 ++++++++++++++++++++++++++++++++++++------------------
>> 1 file changed, 62 insertions(+), 30 deletions(-)
>>
>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
>> index 8a63b4c..7f8cd1b 100644
>> --- a/arch/arm/mm/init.c
>> +++ b/arch/arm/mm/init.c
>> @@ -22,6 +22,7 @@
>> #include <linux/memblock.h>
>> #include <linux/dma-contiguous.h>
>> #include <linux/sizes.h>
>> +#include <linux/stop_machine.h>
>>
>> #include <asm/cp15.h>
>> #include <asm/mach-types.h>
>> @@ -627,12 +628,10 @@ static struct section_perm ro_perms[] = {
>> * safe to be called with preemption disabled, as under stop_machine().
>> */
>> static inline void section_update(unsigned long addr, pmdval_t mask,
>> - pmdval_t prot)
>> + pmdval_t prot, struct mm_struct *mm)
>> {
>> - struct mm_struct *mm;
>> pmd_t *pmd;
>>
>> - mm = current->active_mm;
>> pmd = pmd_offset(pud_offset(pgd_offset(mm, addr), addr), addr);
>>
>> #ifdef CONFIG_ARM_LPAE
>> @@ -656,49 +655,82 @@ static inline bool arch_has_strict_perms(void)
>> return !!(get_cr() & CR_XP);
>> }
>>
>> -#define set_section_perms(perms, field) { \
>> - size_t i; \
>> - unsigned long addr; \
>> - \
>> - if (!arch_has_strict_perms()) \
>> - return; \
>> - \
>> - for (i = 0; i < ARRAY_SIZE(perms); i++) { \
>> - if (!IS_ALIGNED(perms[i].start, SECTION_SIZE) || \
>> - !IS_ALIGNED(perms[i].end, SECTION_SIZE)) { \
>> - pr_err("BUG: section %lx-%lx not aligned to %lx\n", \
>> - perms[i].start, perms[i].end, \
>> - SECTION_SIZE); \
>> - continue; \
>> - } \
>> - \
>> - for (addr = perms[i].start; \
>> - addr < perms[i].end; \
>> - addr += SECTION_SIZE) \
>> - section_update(addr, perms[i].mask, \
>> - perms[i].field); \
>> - } \
>> +void set_section_perms(struct section_perm *perms, int n, bool set,
>> + struct mm_struct *mm)
>> +{
>> + size_t i;
>> + unsigned long addr;
>> +
>> + if (!arch_has_strict_perms())
>> + return;
>> +
>> + for (i = 0; i < n; i++) {
>> + if (!IS_ALIGNED(perms[i].start, SECTION_SIZE) ||
>> + !IS_ALIGNED(perms[i].end, SECTION_SIZE)) {
>> + pr_err("BUG: section %lx-%lx not aligned to %lx\n",
>> + perms[i].start, perms[i].end,
>> + SECTION_SIZE);
>> + continue;
>> + }
>> +
>> + for (addr = perms[i].start;
>> + addr < perms[i].end;
>> + addr += SECTION_SIZE)
>> + section_update(addr, perms[i].mask,
>> + set ? perms[i].prot : perms[i].clear, mm);
>> + }
>> +
>> }
>>
>> -static inline void fix_kernmem_perms(void)
>> +static void update_sections_early(struct section_perm perms[], int n)
>> {
>> - set_section_perms(nx_perms, prot);
>> + struct task_struct *t, *s;
>> +
>> + read_lock(&tasklist_lock);
>> + for_each_process(t) {
>> + if (t->flags & PF_KTHREAD)
>> + continue;
>> + for_each_thread(t, s)
>> + set_section_perms(perms, n, true, s->mm);
>> + }
>> + read_unlock(&tasklist_lock);
>> + set_section_perms(perms, n, true, current->active_mm);
>> + set_section_perms(perms, n, true, &init_mm);
>> +}
>> +
>> +int __fix_kernmem_perms(void *unused)
>> +{
>> + update_sections_early(nx_perms, ARRAY_SIZE(nx_perms));
>> + return 0;
>> +}
>> +
>> +void fix_kernmem_perms(void)
>> +{
>> + stop_machine(__fix_kernmem_perms, NULL, NULL);
>> }
>>
>> #ifdef CONFIG_DEBUG_RODATA
>> +int __mark_rodata_ro(void *unused)
>> +{
>> + update_sections_early(ro_perms, ARRAY_SIZE(ro_perms));
>> + return 0;
>> +}
>> +
>> void mark_rodata_ro(void)
>> {
>> - set_section_perms(ro_perms, prot);
>> + stop_machine(__mark_rodata_ro, NULL, NULL);
>> }
>>
>> void set_kernel_text_rw(void)
>> {
>> - set_section_perms(ro_perms, clear);
>> + set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), false,
>> + current->active_mm);
>> }
>>
>> void set_kernel_text_ro(void)
>> {
>> - set_section_perms(ro_perms, prot);
>> + set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), true,
>> + current->active_mm);
>> }
>> #endif /* CONFIG_DEBUG_RODATA */
>>
>> --
>> 2.5.0
>>
>
>
>
> --
> Kees Cook
> Chrome OS Security
--
Kees Cook
Chrome OS & Brillo Security
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