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From: Ard Biesheuvel <ardb@kernel.org>
To: Evgeniy Baskov <baskov@ispras.ru>
Cc: Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexey Khoroshilov <khoroshilov@ispras.ru>,
	lvc-project@linuxtesting.org, x86@kernel.org,
	linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH 03/16] x86/boot: Set cr0 to known state in trampoline
Date: Wed, 19 Oct 2022 09:06:45 +0200	[thread overview]
Message-ID: <CAMj1kXHUiBO0d926eWTtWZp_hvwHsVLzzn+fdS1EYoXHxpH+iA@mail.gmail.com> (raw)
In-Reply-To: <a155c20eec6343d34b3bdf40c024ce8b35a90e02.1662459668.git.baskov@ispras.ru>

On Tue, 6 Sept 2022 at 12:41, Evgeniy Baskov <baskov@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@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
>

  reply	other threads:[~2022-10-19  7:07 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-06 10:41 [PATCH 00/16] x86_64: Improvements at compressed kernel stage Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 01/16] x86/boot: Align vmlinuz sections on page size Evgeniy Baskov
2022-10-19  7:01   ` Ard Biesheuvel
2022-10-20 11:13     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 02/16] x86/build: Remove RWX sections and align on 4KB Evgeniy Baskov
2022-10-19  7:04   ` Ard Biesheuvel
2022-10-20 11:15     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 03/16] x86/boot: Set cr0 to known state in trampoline Evgeniy Baskov
2022-10-19  7:06   ` Ard Biesheuvel [this message]
2022-10-20 11:23     ` Evgeniy Baskov
2022-10-19  7:44   ` Andrew Cooper
2022-10-20 13:25     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 04/16] x86/boot: Increase boot page table size Evgeniy Baskov
2022-10-19  7:08   ` Ard Biesheuvel
2022-10-20 11:29     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 05/16] x86/boot: Support 4KB pages for identity mapping Evgeniy Baskov
2022-10-19  7:11   ` Ard Biesheuvel
2022-10-20 11:30     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 06/16] x86/boot: Setup memory protection for bzImage code Evgeniy Baskov
2022-10-19  7:17   ` Ard Biesheuvel
2022-10-20 12:07     ` Evgeniy Baskov
2022-10-19  7:57   ` Andrew Cooper
2022-10-20 13:30     ` Evgeniy Baskov
2022-10-20 16:51       ` Andrew Cooper
2022-09-06 10:41 ` [PATCH 07/16] x86/boot: Map memory explicitly Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 08/16] x86/boot: Remove mapping from page fault handler Evgeniy Baskov
2022-10-19  7:20   ` Ard Biesheuvel
2022-09-06 10:41 ` [PATCH 09/16] efi/libstub: Move helper function to related file Evgeniy Baskov
2022-10-19  7:21   ` Ard Biesheuvel
2022-09-06 10:41 ` [PATCH 10/16] x86/boot: Make console interface more abstract Evgeniy Baskov
2022-10-19  7:23   ` Ard Biesheuvel
2022-10-20 12:10     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 11/16] x86/boot: Split trampoline and pt init code Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 12/16] x86/boot: Add EFI kernel extraction interface Evgeniy Baskov
2022-10-19  7:27   ` Ard Biesheuvel
2022-10-20 12:14     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 13/16] efi/x86: Support extracting kernel from libstub Evgeniy Baskov
2022-10-19  7:35   ` Ard Biesheuvel
2022-10-20 12:36     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 14/16] x86/build: Make generated PE more spec compliant Evgeniy Baskov
2022-10-19  7:39   ` Ard Biesheuvel
2022-10-20 13:07     ` Evgeniy Baskov
2022-09-06 10:41 ` [PATCH 15/16] efi/libstub: Add memory attribute protocol definitions Evgeniy Baskov
2022-10-19  7:39   ` Ard Biesheuvel
2022-09-06 10:41 ` [PATCH 16/16] efi/libstub: Use memory attribute protocol Evgeniy Baskov
2022-10-18 20:51   ` [PATCH] efi/libstub: make memory protection warnings include newlines Peter Jones
2022-10-19  7:44     ` Ard Biesheuvel
2022-10-19  7:42   ` [PATCH 16/16] efi/libstub: Use memory attribute protocol Ard Biesheuvel
2022-10-20 13:13     ` Evgeniy Baskov
2022-10-18 21:04 ` [PATCH 00/16] x86_64: Improvements at compressed kernel stage Peter Jones
2022-10-20 11:05   ` Evgeniy Baskov

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