linux-kernel - Re: [PATCH] x86/sev: Add ENCODE_FRAME_POINTER after stack changed for #VC

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Date:   Thu, 17 Mar 2022 15:19:43 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Joerg Roedel <jroedel@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/sev: Add ENCODE_FRAME_POINTER after stack changed
 for #VC

On Wed, Mar 16, 2022 at 12:16:12PM +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <jiangshan.ljs@...group.com>
> 
> In idtentry_vc(), the real frame is changed after it switches to new
> stack, ENCODE_FRAME_POINTER should be called in case for unwinder.
> 
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
> ---
>  arch/x86/entry/entry_64.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index e20eabaa56b8..f99f2881ed83 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -540,6 +540,7 @@ SYM_CODE_START(\asmsym)
>  	call	vc_switch_off_ist
>  	movq	%rax, %rsp		/* Switch to new stack */
>  
> +	ENCODE_FRAME_POINTER
>  	UNWIND_HINT_REGS
>  
>  	/* Update pt_regs */

Looks right to me.  Any chance you have the ability to test this
scenario by unwinding from #VC with CONFIG_FRAME_POINTER?

-- 
Josh