linux-kernel - Re: [PATCH] x86/bugs: Don't warn when overwriting retbleed_return_thunk with srso_return

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Message-ID: <20250515172355.GIaCYjK_fz-n71Aruz@fat_crate.local>
Date: Thu, 15 May 2025 19:23:55 +0200
From: Borislav Petkov <bp@...en8.de>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Suraj Jitindar Singh <surajjs@...zon.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, stable@...r.kernel.org
Subject: Re: [PATCH] x86/bugs: Don't warn when overwriting
 retbleed_return_thunk with srso_return_thunk

On Thu, May 15, 2025 at 10:06:33AM -0700, Pawan Gupta wrote:
> As I said above, a mitigation unintentionally make another mitigation
> ineffective.

I actually didn't need an analysis - my point is: if you're going to warn
about it, then make it big so that it gets caught.

> Yes, maybe a WARN_ON() conditional to sanity checks for retbleed/SRSO.

Yes, that.

At least.

The next step would be if this whole "let's set a thunk without overwriting
a previously set one" can be fixed differently.

For now, though, the *least* what should be done here is catch the critical
cases where a mitigation is rendered ineffective. And warning Joe Normal User
about it doesn't bring anything. We do decide for the user what is safe or
not, practically. At least this has been the strategy until now.

So the goal here should be to make Joe catch this and tell us to fix it.

Makes sense?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette