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SubjectRe: [PATCH qemu] x86: don't let decompressed kernel image clobber setup_data

On 1.1.2023 6.33, H. Peter Anvin wrote:
> On 12/31/22 10:22, Jason A. Donenfeld wrote:
>> On Sat, Dec 31, 2022 at 03:24:32PM +0100, Borislav Petkov wrote:
>>> On Sat, Dec 31, 2022 at 02:51:28PM +0100, Jason A. Donenfeld wrote:
>>>> That failure is unrelated to the ident mapping issue Peter and
>>>> I discussed. The original failure is described in the commit message:
>>>> decompression clobbers the data, so sd->next points to garbage.
>>> Right
>> So with that understanding confirmed, I'm confused at your surprise that
>> hpa's unrelated fix to the different issue didn't fix this issue.
> If decompression does clobber the data, then we *also* need to figure
> out why that is. There are basically three possibilities:
> 1. If physical KASLR is NOT used:
>     a. The boot loader doesn't honor the kernel safe area properly;
>     b. Somewhere in the process a bug in the calculation of the
>        kernel safe area has crept in.
> 2. If physical KASLR IS used:
>     The decompressor doesn't correctly keep track of nor relocate
>     all the keep-out zones before picking a target address.

Seems setup_data is not included in those mem_avoid regions.

> One is a bootloader bug, two is a kernel bug. My guess is (2) is the
> culprit, but (1b) should be checked, too.
>     -hpa


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