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SubjectRe: [PATCH v5 03/27] x86/boot: Set cr0 to known state in trampoline
On Tue, Mar 14, 2023 at 01:13:30PM +0300, Evgeniy Baskov wrote:
> Ensure WP bit to be set to prevent boot code from writing to
> non-writable memory pages.
>
> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> Signed-off-by: Evgeniy Baskov <baskov@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 03c4328a88cb..01fa42d31648 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -660,9 +660,8 @@ SYM_CODE_START(trampoline_32bit_src)
> pushl $__KERNEL_CS
> pushl %eax
>
> - /* Enable paging again. */
> - movl %cr0, %eax
> - btsl $X86_CR0_PG_BIT, %eax
> + /* Enable paging and set CR0 to known state (this also sets WP flag) */
> + movl $CR0_STATE, %eax

This sets a lot more than WP. Why?

--
Regards/Gruss,
Boris.

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