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

["Mika Penttilä" <mika.penttila@mbosol.com>]

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
> 


--Mika