linux-kernel - Re: [PATCH 5.6 096/166] x86/xen: Make the boot CPU idle task reliable

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Date:   Wed, 22 Apr 2020 12:45:32 +0200
From:   Jürgen Groß <jgross@...e.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Miroslav Benes <mbenes@...e.cz>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.6 096/166] x86/xen: Make the boot CPU idle task reliable

On 22.04.20 11:57, Greg Kroah-Hartman wrote:
> From: Miroslav Benes <mbenes@...e.cz>
> 
> [ Upstream commit 2f62f36e62daec43aa7b9633ef7f18e042a80bed ]
> 
> The unwinder reports the boot CPU idle task's stack on XEN PV as
> unreliable, which affects at least live patching. There are two reasons
> for this. First, the task does not follow the x86 convention that its
> stack starts at the offset right below saved pt_regs. It allows the
> unwinder to easily detect the end of the stack and verify it. Second,
> startup_xen() function does not store the return address before jumping
> to xen_start_kernel() which confuses the unwinder.
> 
> Amend both issues by moving the starting point of initial stack in
> startup_xen() and storing the return address before the jump, which is
> exactly what call instruction does.
> 
> Signed-off-by: Miroslav Benes <mbenes@...e.cz>
> Reviewed-by: Juergen Gross <jgross@...e.com>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

You'll need upstream d6f34f4c6b4a96 ("x86/xen: fix booting 32-bit pv
guest"), too.


Juergen