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

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Message-ID: <Y7JzTh8JnMXM6ZPS@zn.tnic>
Date:   Mon, 2 Jan 2023 07:01:50 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>, 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 Sat, Dec 31, 2022 at 07:31:21PM -0800, H. Peter Anvin wrote:
> 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.

Yeah, we will probably need that too.

Btw, looka here - it can't get any more obvious than that after dumping
setup_data too:

early console in setup code
early console in extract_kernel
input_data: 0x00000000040f92bf
input_len: 0x0000000000f1c325
output: 0x0000000001000000
output_len: 0x0000000003c5e7d8
kernel_total_size: 0x0000000004428000
needed_size: 0x0000000004600000
boot_params->hdr.setup_data: 0x00000000010203b0
trampoline_32bit: 0x000000000009d000

Decompressing Linux... Parsing ELF... done.
Booting the kernel.
<EOF>

Aligning them vertically:

output:				0x0000000001000000
output_len:			0x0000000003c5e7d8
kernel_total_size:		0x0000000004428000
needed_size:			0x0000000004600000
boot_params->hdr.setup_data:	0x00000000010203b0

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette