linux-kernel - Re: WARNING: kernel stack frame pointer at ffffffff82e03f40 in swapper:0 has bad value (null)

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Date:   Mon, 12 Dec 2016 23:33:54 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: WARNING: kernel stack frame pointer at ffffffff82e03f40 in
 swapper:0 has bad value           (null)

On Mon, Dec 12, 2016 at 04:11:47PM -0600, Josh Poimboeuf wrote:
> Yes, please.

Attached.

> That said, the code could probably be made a little clearer by changing
> "call 1f" to "push $1f" and then move the '1' label to after the lretq
> instruction, like:
> 
> 	pushq	$1f		# put return address on stack for unwinder
> 	xorq	%rbp, %rbp	# clear frame pointer
> 	movq	initial_code(%rip), %rax
> 	pushq	$__KERNEL_CS	# set correct cs
> 	pushq	%rax		# target address in negative space
> 	lretq
> 1:
> ENDPROC(start_cpu)
> 
> That shows:
> 
>   start_cpu+0x14/0x14
> 
> Which is more accurate anyway.  I'll make a patch.

Yap, makes more sense. I'll run it tomorrow.

FWIW, I tried

	pushq $1f

before without moving the 1: label but the thing still fired.

-- 
Regards/Gruss,
    Boris.

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