linux-hardening - Re: [PATCH 06/16] x86/boot: Setup memory protection for bzImage code

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Date:   Thu, 20 Oct 2022 16:51:00 +0000
From:   Andrew Cooper <Andrew.Cooper3@...rix.com>
To:     Evgeniy Baskov <baskov@...ras.ru>
CC:     Ard Biesheuvel <ardb@...nel.org>, 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>,
        "lvc-project@...uxtesting.org" <lvc-project@...uxtesting.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>
Subject: Re: [PATCH 06/16] x86/boot: Setup memory protection for bzImage code

On 20/10/2022 14:30, Evgeniy Baskov wrote:
> On 2022-10-19 10:57, Andrew Cooper wrote:
>> On 06/09/2022 11:41, Evgeniy Baskov wrote:
>>> diff --git a/arch/x86/boot/compressed/head_64.S
>>> b/arch/x86/boot/compressed/head_64.S
>>> index 5273367283b7..889ca7176aa7 100644
>>> --- a/arch/x86/boot/compressed/head_64.S
>>> +++ b/arch/x86/boot/compressed/head_64.S
>>> @@ -602,6 +603,28 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
>>>      jmp    *%rax
>>>  SYM_FUNC_END(.Lrelocated)
>>>
>>> +SYM_FUNC_START_LOCAL_NOALIGN(startup32_enable_nx_if_supported)
>>> +    pushq    %rbx
>>> +
>>> +    leaq    has_nx(%rip), %rcx
>>> +
>>> +    mov    $0x80000001, %eax
>>> +    cpuid
>>> +    btl    $20, %edx
>>
>> btl $(X86_FEATURE_NX & 31), %edx
>>
>> But also need to check for the availability of the extended leaf in the
>> first place.
>
> Yes, thank you for suggestion, that looks more readable. I will
> also add the leaf node check. Is there any processor though that
> supports long mode and does not support 0x80000001 leaf node?

No, good point.  The Long Mode feature bit is in this leaf too.

~Andrew