linux-kernel - AVX register corruption from signal delivery

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Message-ID: <c87e93c3-5f30-f242-74b7-6c7ccc91158a@google.com>
Date:   Tue, 26 Nov 2019 14:49:55 -0500
From:   Barret Rhoden <brho@...gle.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Rik van Riel\"" <riel@...riel.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Subject: AVX register corruption from signal delivery

Hi -

The Go Team found a bug[1] where the AVX registers can get corrupted 
during signal delivery.  They were able to bisect it to commits related 
to the "x86: load FPU registers on return to userland" patchset[2].

The bug requires the kernel to be built with GCC 9 to trigger.  In 
particular, arch/x86/kernel/fpu/signal.c needs to be built with GCC 9.

Thanks,

Barret

[1] https://bugzilla.kernel.org/show_bug.cgi?id=205663
[2] 
https://lore.kernel.org/kvm/20190403164156.19645-1-bigeasy@linutronix.de/