linux-kernel - Re: [PATCH qemu] x86: don't let decompressed kernel image clobber setup

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Date:   Sat, 31 Dec 2022 21:13:05 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Mika Penttilä <mika.penttila@...sol.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     pbonzini@...hat.com, ebiggers@...nel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, qemu-devel@...gnu.org,
        ardb@...nel.org, kraxel@...hat.com, philmd@...aro.org
Subject: Re: [PATCH qemu] x86: don't let decompressed kernel image clobber
 setup_data

On 12/31/22 20:55, Mika Penttilä wrote:
>>
>> 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.
> 

[facepalm]


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

Correction: two are kernel bugs, i.e. (1b) and (2) are both kernel bugs.

	-hpa