From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C02EC43441 for ; Fri, 9 Nov 2018 17:53:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DB30B20818 for ; Fri, 9 Nov 2018 17:53:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linaro.org header.i=@linaro.org header.b="OBSZVuIT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB30B20818 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728606AbeKJDfB (ORCPT ); Fri, 9 Nov 2018 22:35:01 -0500 Received: from mail-io1-f68.google.com ([209.85.166.68]:42259 "EHLO mail-io1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728108AbeKJDfB (ORCPT ); Fri, 9 Nov 2018 22:35:01 -0500 Received: by mail-io1-f68.google.com with SMTP id h19-v6so1855998iog.9 for ; Fri, 09 Nov 2018 09:53:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=XTY12vXA7XYaAuO9OtQgJnKFSQxposuOzbrrHwRbAHY=; b=OBSZVuITrHPRPdyopuniyWsHRA/vgZL/bh0nXdE/cE5hAHQqrx1VtDStc+U16vXHu6 KS30YOFc0+xUX1+3OpFUs4/0jMiB6hv8APvRuDzWvagtcHPUelsOaGPDok+zhfdue9Gh xwWIF38vlCZPy/m2H+y1tpOPxYOM2Oqt//yXI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=XTY12vXA7XYaAuO9OtQgJnKFSQxposuOzbrrHwRbAHY=; b=fnei6F7NbQ5+4FAuUuMrWXqy36kd32ub9QLKRZUnW3oxlwXyMyMEjOXNN4G8e/Sht/ oGGA5jQij0kVFFKvKZmxoPRrwiWLLQgCQV0MLHVsVN9uTU+bhdW3EWkb6b7ouA6IV6VZ PlWi3Denukc5mw5lP8AZ5+RWztzaQH2VUyFokmJRrulKPOj8OUUexBt8VqlEq+pRcEmU u5B9kbvsF/xolylWCYuoRVx5KjnM8ThbOrdfWkXgMA9MQ46YutNh6wwz2WcxQNuFWCbE Kjbi2xcUJ51s3ihUA1Eh/L/Ocb+uY3vftDHLxNgLswsPo/MUOz74Wn9XyXlZ9DF0b00A jV0w== X-Gm-Message-State: AGRZ1gLijo4k8ZUhgTB6l2jKdP5by7Xp4vnEhP7D0M33XSQZtdE5emR6 FJN/2vuTSHrf7QAdPvWsKzq0HRU94ujBC1gDx4ManA== X-Google-Smtp-Source: AJdET5fV0GoE8Huo6ufH+PbnKP+ZLYZjqm9wJW0b6WaXxR+l+VeaX7tbCJqsgjVrqQ4faGq+C0FPRzrNQEX5Tc7XTmo= X-Received: by 2002:a6b:37c2:: with SMTP id e185-v6mr7855956ioa.173.1541786001791; Fri, 09 Nov 2018 09:53:21 -0800 (PST) MIME-Version: 1.0 Received: by 2002:a6b:4f16:0:0:0:0:0 with HTTP; Fri, 9 Nov 2018 09:53:21 -0800 (PST) In-Reply-To: References: <3cf04e113d71c9f8e4be95fb84a510f085aa4afa.1541711457.git.jpoimboe@redhat.com> <20181109151028.faifw66enzye32gg@treble> <20181109173106.kbghzsdsu7oachl6@treble> <20181109174608.eahqh4fkyl3k2gvs@treble> From: Ard Biesheuvel Date: Fri, 9 Nov 2018 18:53:21 +0100 Message-ID: Subject: Re: [RFC PATCH 1/3] static_call: Add static call infrastructure To: Josh Poimboeuf Cc: Linux Kernel Mailing List , "the arch/x86 maintainers" , Andy Lutomirski , Steven Rostedt , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Masami Hiramatsu , Jason Baron , Jiri Kosina , David Laight , Borislav Petkov Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9 November 2018 at 18:52, Ard Biesheuvel wrote: > On 9 November 2018 at 18:46, Josh Poimboeuf wrote: >> On Fri, Nov 09, 2018 at 06:33:03PM +0100, Ard Biesheuvel wrote: >>> On 9 November 2018 at 18:31, Josh Poimboeuf wrote: >>> > On Fri, Nov 09, 2018 at 06:25:24PM +0100, Ard Biesheuvel wrote: >>> >> On 9 November 2018 at 16:14, Ard Biesheuvel wrote: >>> >> > On 9 November 2018 at 16:10, Josh Poimboeuf wrote: >>> >> >> On Fri, Nov 09, 2018 at 02:39:17PM +0100, Ard Biesheuvel wrote: >>> >> >>> > + for (site = start; site < stop; site++) { >>> >> >>> > + struct static_call_key *key = static_call_key(site); >>> >> >>> > + unsigned long addr = static_call_addr(site); >>> >> >>> > + >>> >> >>> > + if (list_empty(&key->site_mods)) { >>> >> >>> > + struct static_call_mod *mod; >>> >> >>> > + >>> >> >>> > + mod = kzalloc(sizeof(*mod), GFP_KERNEL); >>> >> >>> > + if (!mod) { >>> >> >>> > + WARN(1, "Failed to allocate memory for static calls"); >>> >> >>> > + return; >>> >> >>> > + } >>> >> >>> > + >>> >> >>> > + mod->sites = site; >>> >> >>> > + list_add_tail(&mod->list, &key->site_mods); >>> >> >>> > + >>> >> >>> > + /* >>> >> >>> > + * The trampoline should no longer be used. Poison it >>> >> >>> > + * it with a BUG() to catch any stray callers. >>> >> >>> > + */ >>> >> >>> > + arch_static_call_poison_tramp(addr); >>> >> >>> >>> >> >>> This patches the wrong thing: the trampoline is at key->func not addr. >>> >> >> >>> >> >> If you look at the x86 implementation, it actually does poison the >>> >> >> trampoline. >>> >> >> >>> >> >> The address of the trampoline isn't actually known here. key->func >>> >> >> isn't the trampoline address; it's the destination func address. >>> >> >> >>> >> >> So instead I passed the address of the call instruction. The arch code >>> >> >> then reads the instruction to find the callee (the trampoline). >>> >> >> >>> >> >> The code is a bit confusing. To make it more obvious, maybe we should >>> >> >> add another arch function to read the call destination. Then this code >>> >> >> can pass that into arch_static_call_poison_tramp(). >>> >> >> >>> >> > >>> >> > Ah right, so I am basically missing a dereference in my >>> >> > arch_static_call_poison_tramp() code if this breaks. >>> >> > >>> >> >>> >> Could we call it 'defuse' rather than 'poision'? On arm64, we will >>> >> need to keep it around to bounce function calls that are out of range, >>> >> and replace it with a PLT sequence. >>> > >>> > Ok, but doesn't that defeat the purpose of the inline approach? >>> > >>> >>> It does. But this only occurs when a module is loaded far away, and >>> this will only happen if you have 2 GB range KASLR enabled, or your >>> 128 MB module region gets exhausted for some reason, so the majority >>> of calls should use a single relative branch. >> >> Makes sense. Do you also account for the possibility that the original >> call emitted by GCC was far away and thus used the PLT? >> > > That doesn't really happen. vmlinux is never over 128 MB, and the > modules are only partially linked, so the linker never gets to the > stage where it needs to emit veneers. > > It's a bit fiddly since inline and out-of-line both use > arch_static_call_transform(), but what I need to do is basically: > > - for out-of-line, the trampoline needs to be patched into a > movn/movk/movk/br sequence if the target is too far > - for inline, the trampoline itself needs to be patched from > adrp/ldr/br (which does a load and a indirect branch) to > movn/movk/movk/br (which uses immediates), and the call sites need to > be patched into calls to the veneer if the target is out of range. > > So arch_static_call_transform() needs to know where the trampoline is > for this use case, so could we perhaps add a 'void *orig' in the key > struct that keeps track of the original value of 'addr' ? ... and pass it to arch_static_call_transform