On Mon, May 9, 2016 at 3:01 PM, Yinghai Lu <ying...@kernel.org> wrote:
> On Mon, May 9, 2016 at 1:22 PM, Kees Cook <keesc...@chromium.org> wrote:
>> As it turns out, mapping_info DOES need to be initialized every
>> time. Without this, page tables were not being corrected updated, which
>> could cause reboots when a physical address beyond 2G was chosen.
>>
>> Signed-off-by: Kees Cook <keesc...@chromium.org>
>> ---
>> arch/x86/boot/compressed/pagetable.c | 16 +++++-----------
>> 1 file changed, 5 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/x86/boot/compressed/pagetable.c
>> b/arch/x86/boot/compressed/pagetable.c
>> index 3c99051566a9..34b95df14e69 100644
>> --- a/arch/x86/boot/compressed/pagetable.c
>> +++ b/arch/x86/boot/compressed/pagetable.c
>> @@ -90,23 +90,17 @@ static void prepare_level4(void)
>> }
>>
>> /*
>> - * Mapping information structure passed to kernel_ident_mapping_init().
>> - * Since this never changes, there's no reason to repeatedly fill it
>> - * in on the stack when calling add_identity_map().
>> - */
>> -static struct x86_mapping_info mapping_info = {
>> - .alloc_pgt_page = alloc_pgt_page,
>> - .context = &pgt_data,
>> - .pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
>> -};
>> -
>> -/*
>> * Adds the specified range to what will become the new identity mappings.
>> * Once all ranges have been added, the new mapping is activated by calling
>> * finalize_identity_maps() below.
>> */
>> void add_identity_map(unsigned long start, unsigned long size)
>> {
>> + struct x86_mapping_info mapping_info = {
>> + .alloc_pgt_page = alloc_pgt_page,
>> + .context = &pgt_data,
>> + .pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
>> + };
>> unsigned long end = start + size;
>
> Still should be assigned once, and should be done in
> prepare_level4(). --- by may need different name for that ?
>
> The exact reason to have assigning in functions.
>
> pgt_data address could be changed during kernel relocation.
> so can not assigned during compiling time.
Ah-ha, that explains why I had to keep it on the stack. Thanks for the
clarification!
-Kees
--
Kees Cook
Chrome OS & Brillo Security
