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SubjectRe: [PATCH 23/62] x86/idt: Move IDT to data segment
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On 12.02.20 17:23, Andy Lutomirski wrote:
>
>
>> On Feb 12, 2020, at 3:55 AM, Joerg Roedel <joro@8bytes.org> wrote:
>>
>> On Tue, Feb 11, 2020 at 02:41:25PM -0800, Andy Lutomirski wrote:
>>>> On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel <joro@8bytes.org> wrote:
>>>>
>>>> From: Joerg Roedel <jroedel@suse.de>
>>>>
>>>> With SEV-ES, exception handling is needed very early, even before the
>>>> kernel has cleared the bss segment. In order to prevent clearing the
>>>> currently used IDT, move the IDT to the data segment.
>>>
>>> Ugh. At the very least this needs a comment in the code.
>>
>> Yes, right, added a comment for that.
>>
>>> I had a patch to fix the kernel ELF loader to clear BSS, which would
>>> fix this problem once and for all, but it didn't work due to the messy
>>> way that the decompressor handles memory. I never got around to
>>> fixing this, sadly.
>>
>> Aren't there other ways of booting (Xen-PV?) which don't use the kernel
>> ELF loader?
>
> Dunno. I would hope the any sane loader would clear BSS before executing anything. This isn’t currently the case, though. Oh well.

Xen-PV is clearing BSS as the very first action.


Juergen

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