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Message-ID: <20190205132953.GF17582@hirez.programming.kicks-ass.net>
Date: Tue, 5 Feb 2019 14:29:53 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>,
Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>,
linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
Thomas Gleixner <tglx@...utronix.de>,
Nadav Amit <nadav.amit@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>, linux_dti@...oud.com,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org, akpm@...ux-foundation.org,
kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
will.deacon@....com, ard.biesheuvel@...aro.org,
kristen@...ux.intel.com, deneen.t.dock@...el.com,
Nadav Amit <namit@...are.com>, Kees Cook <keescook@...omium.org>,
Dave Hansen <dave.hansen@...el.com>,
Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v2 06/20] x86/alternative: use temporary mm for text
poking
On Tue, Feb 05, 2019 at 12:31:46PM +0100, Peter Zijlstra wrote:
> In general, text_poke() cannot fail:
>
> - suppose changing a single jump label requires poking multiple sites
> (not uncommon), we fail halfway through and then have to undo the
> first pokes, but those pokes fail again.
>
> - this then leaves us no way forward and no way back, we've got
> inconsistent text state -> FAIL.
Note that this exact fail scenario still exists in the CPU hotplug code.
See kernel/cpu.c:cpuhp_thread_fun():
/*
* If we fail on a rollback, we're up a creek without no
* paddle, no way forward, no way back. We loose, thanks for
* playing.
*/
WARN_ON_ONCE(st->rollback);
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