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

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Message-ID: <Y7A8QiYgoYU3QdLm@zx2c4.com>
Date:   Sat, 31 Dec 2022 14:42:26 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "H. Peter Anvin" <hpa@...or.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 02:35:45PM +0100, Borislav Petkov wrote:
> On Sat, Dec 31, 2022 at 01:54:50PM +0100, Jason A. Donenfeld wrote:
> > Nothing special... `-kernel bzImage` should be enough to do it. Eric
> > reported it, and then I was able to repro trivially. Sure you got the
> > right version?
> 
> Yeah, qemu executables confusion here - had wrongly something older of the
> version 7.1...
> 
> Now made sure I'm actually booting with the latest qemu:
> 
> QEMU emulator version 7.2.50 (v7.2.0-333-g222059a0fccf)
> 
> With that the kernel with your config hangs early during boot and the stack
> trace is below.
> 
> Seeing how it says trapnr 14, then that looks like something you are seeing.
> 
> But lemme poke at it more.

Yes. The cause is what I've described in the commit message. There are
two proposed fixes, the v1, which has the 62 MiB limitation due to a
kernel bug, and the v3, which seems to work fine, and is simpler, and I
suspect that's the one QEMU upstream should take.

https://lore.kernel.org/lkml/20221230220725.618763-1-Jason@zx2c4.com/