[lvc-project] [PATCH 03/16] x86/boot: Set cr0 to known state in trampoline

Wed Oct 19 10:06:45 MSK 2022

On Tue, 6 Sept 2022 at 12:41, Evgeniy Baskov <baskov at ispras.ru> wrote:
>> Ensure WP bit to be set to prevent boot code from writing to
> non-writable memory pages.
>> Signed-off-by: Evgeniy Baskov <baskov at ispras.ru>
> ---
> arch/x86/boot/compressed/head_64.S | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index d33f060900d2..5273367283b7 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -619,9 +619,8 @@ SYM_CODE_START(trampoline_32bit_src)
> /* Set up new stack */
> leal TRAMPOLINE_32BIT_STACK_END(%ecx), %esp
>> - /* Disable paging */
> - movl %cr0, %eax
> - btrl $X86_CR0_PG_BIT, %eax

Why do we no longer care about CR0's prior value?
> + /* Disable paging and setup CR0 */
> + movl $(CR0_STATE & ~X86_CR0_PG), %eax
> movl %eax, %cr0
>> /* Check what paging mode we want to be in after the trampoline */
> --
> 2.35.1
>