linux-hardening - Re: [PATCH v4 06/26] x86/boot: Setup memory protection for bzImage code

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Date:   Wed, 08 Mar 2023 19:15:20 +0300
From:   Evgeniy Baskov <baskov@...ras.ru>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Peter Jones <pjones@...hat.com>,
        "Limonciello, Mario" <mario.limonciello@....com>,
        joeyli <jlee@...e.com>, lvc-project@...uxtesting.org,
        x86@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 06/26] x86/boot: Setup memory protection for bzImage
 code

On 2023-03-08 13:47, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:38, Evgeniy Baskov <baskov@...ras.ru> wrote:
>> 
>> Use previously added code to use 4KB pages for mapping. Map compressed
>> and uncompressed kernel with appropriate memory protection attributes.
>> For compressed kernel set them up manually. For uncompressed kernel
>> used flags specified in ELF header.
>> 
>> Tested-by: Mario Limonciello <mario.limonciello@....com>
>> Tested-by: Peter Jones <pjones@...hat.com>
>> Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
>> 
> 
> This patch breaks the 'nokaslr' command line option (at least with
> SeaBIOS) unless I apply the hunk below:
> 

Oh, I didn't think of that option.. Thanks!
I will also add the check to the identity mapping,
so the warning won't be emitted with 'nokaslr'.

> 
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -329,7 +329,8 @@ static size_t parse_elf(void *output, unsigned
> long output_len,
> 
>         handle_relocations(output, output_len, virt_addr);
> 
> -       if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
> +       if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE) ||
> +           cmdline_find_option_bool("nokaslr"))
>                 goto skip_protect;
> 
>         for (i = 0; i < ehdr.e_phnum; i++) {
> @@ -481,8 +482,10 @@ asmlinkage __visible void *extract_kernel(void
> *rmode, memptr heap,
>          * If KASLR is disabled input and output regions may overlap.
>          * In this case we need to map region excutable as well.
>          */
> -       unsigned long map_flags = MAP_ALLOC | MAP_WRITE |
> -                       (IS_ENABLED(CONFIG_RANDOMIZE_BASE) ? 0 : 
> MAP_EXEC);
> +       unsigned long map_flags = MAP_ALLOC | MAP_WRITE;
> +       if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE) ||
> +           cmdline_find_option_bool("nokaslr"))
> +               map_flags |= MAP_EXEC;
>         phys_addr = kernel_add_identity_map(phys_addr,
>                                             phys_addr + needed_size,
>                                             map_flags);