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?
-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
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