linux-kernel - Re: [PATCH 08/15] x86/alternatives: Teach text_poke

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Message-ID: <20190610165752.2feozekuqbincj3d@treble>
Date:   Mon, 10 Jun 2019 11:57:52 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>,
        David Laight <David.Laight@...LAB.COM>,
        Borislav Petkov <bp@...en8.de>,
        Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Nadav Amit <namit@...are.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Edward Cree <ecree@...arflare.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH 08/15] x86/alternatives: Teach text_poke_bp() to emulate
 instructions

On Wed, Jun 05, 2019 at 03:08:01PM +0200, Peter Zijlstra wrote:
> In preparation for static_call support, teach text_poke_bp() to
> emulate instructions, including CALL.
> 
> The current text_poke_bp() takes a @handler argument which is used as
> a jump target when the temporary INT3 is hit by a different CPU.
> 
> When patching CALL instructions, this doesn't work because we'd miss
> the PUSH of the return address. Instead, teach poke_int3_handler() to
> emulate an instruction, typically the instruction we're patching in.
> 
> This fits almost all text_poke_bp() users, except
> arch_unoptimize_kprobe() which restores random text, and for that site
> we have to build an explicit emulate instruction.
> 
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Nadav Amit <namit@...are.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh