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

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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