linux-kernel - Re: [PATCH -v2] x86/retpoline: Ensure default return thunk isn't used at runtime

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Message-ID: <20240207194919.qw4jk2ykadjn5d4e@treble>
Date: Wed, 7 Feb 2024 11:49:19 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: "Kaplan, David" <David.Kaplan@....com>, Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tip-commits@...r.kernel.org" <linux-tip-commits@...r.kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	"x86@...nel.org" <x86@...nel.org>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH -v2] x86/retpoline: Ensure default return thunk isn't
 used at runtime

On Wed, Feb 07, 2024 at 07:53:28PM +0100, Borislav Petkov wrote:
> On Wed, Feb 07, 2024 at 09:50:10AM -0800, Josh Poimboeuf wrote:
> > And as you say, there are many frankenkernels out there and upstream
> > doesn't want to be in the business of debugging them.
> 
> Ok, all valid points. Diff ontop.
> 
> I'll queue it now so that it has ample time of cooking in linux-next.
> 
> Thx.
> 
> ---
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 612c9ec456ae..5a300a7bad04 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -2853,16 +2853,5 @@ ssize_t cpu_show_gds(struct device *dev, struct device_attribute *attr, char *bu
>  
>  void __warn_thunk(void)
>  {
> -	pr_warn_once("\n");
> -	pr_warn_once("**********************************************************\n");
> -	pr_warn_once("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
> -	pr_warn_once("**                                                      **\n");
> -	pr_warn_once("**   Unpatched return thunk in use. This should not     **\n");
> -	pr_warn_once("**   happen on a production kernel. Please report this  **\n");
> -	pr_warn_once("**   to x86@...nel.org.                                 **\n");
> -	pr_warn_once("**                                                      **\n");
> -	pr_warn_once("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
> -	pr_warn_once("**********************************************************\n");
> -
> -	dump_stack();
> +	WARN_ONCE(1, "Unpatched return thunk in use. This should not happen!\n");
>  }

LGTM, thanks!

-- 
Josh