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

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Date:   Sat, 31 Dec 2022 19:31:21 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Borislav Petkov <bp@...en8.de>,
        "Jason A. Donenfeld" <Jason@...c4.com>
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 19:21, H. Peter Anvin wrote:
>>
>>> Alternatively, setup_data could be relocated, the boot param protocol
>>> could be bumped, and then QEMU could conditionalized it's use of
>>> setup_data based on that protocol version. That'd work, but seems a bit
>>> more involved.
>>
>> I think this is at least worth considering because the kernel overwriting
>> setup_data after having been told where that setup_data is located is 
>> not really
>> nice.
>>
>> Well not explicitly at least - it gets the pointer to the first 
>> element and
>> something needs to traverse that list to know which addresses are 
>> live. But
>> still, that info is there so perhaps we need to take setup_data into
>> consideration too before decompressing...
>>

It would probably be a good idea to add a "maximum physical address for 
initrd/setup_data/cmdline" field to struct kernel_info, though. It 
appears right now that those fields are being identity-mapped in the 
decompressor, and that means that if 48-bit addressing is used, physical 
memory may extend past the addressable range.

	-hpa