From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S934942AbeAOQv2 (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Mon, 15 Jan 2018 11:51:28 -0500
Received: from merlin.infradead.org ([205.233.59.134]:41214 "EHLO
        merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S934464AbeAOQua (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 15 Jan 2018 11:50:30 -0500
Message-Id: <20180115164909.894255586@infradead.org>
User-Agent: quilt/0.63-1
Date: Mon, 15 Jan 2018 17:44:31 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: David Woodhouse <dwmw2@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-kernel@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>
Subject: [PATCH 3/4] x86/jump_label: Implement arch_static_assert()
References: <20180115164428.498966552@infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Disposition: inline; filename=peterz-x86-asm-goto-assert.patch
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

Implement the static (branch) assertion. It simply emits the address
of the next instruction into a special section which objtool will read
and validate against either __jump_table or .altinstructions.

Use like:

	if (static_branch_likely(_key)) {
		arch_static_assert();
		/* do stuff */
	}

Or

	if (static_cpu_has(_feat)) {
		arch_static_assert();
		/* do stuff */
	}

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/jump_label.h |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -62,6 +62,15 @@ static __always_inline bool arch_static_
 	return true;
 }
 
+static __always_inline void arch_static_assert(void)
+{
+	asm volatile ("1:\n\t"
+		      ".pushsection .discard.jump_assert, \"aw\" \n\t"
+		      _ASM_ALIGN  "\n\t"
+		      _ASM_PTR "1b \n\t"
+		      ".popsection \n\t");
+}
+
 #ifdef CONFIG_X86_64
 typedef u64 jump_label_t;
 #else