From patchwork Fri Oct 5 08:13:25 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ard Biesheuvel X-Patchwork-Id: 979351 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 42RMyy1SjYz9s3T for ; Fri, 5 Oct 2018 18:16:10 +1000 (AEST) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=linaro.org header.i=@linaro.org header.b="MWd+hOYP"; dkim-atps=neutral Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 42RMyx6vj7zF3RB for ; Fri, 5 Oct 2018 18:16:09 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linaro.org Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=linaro.org header.i=@linaro.org header.b="MWd+hOYP"; dkim-atps=neutral X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=linaro.org (client-ip=2a00:1450:4864:20::344; helo=mail-wm1-x344.google.com; envelope-from=ard.biesheuvel@linaro.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linaro.org Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linaro.org header.i=@linaro.org header.b="MWd+hOYP"; dkim-atps=neutral Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 42RMw70nrtzF3Jh for ; Fri, 5 Oct 2018 18:13:42 +1000 (AEST) Received: by mail-wm1-x344.google.com with SMTP id a8-v6so1022890wmf.1 for ; Fri, 05 Oct 2018 01:13:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=M974k2iyDJIOjsCt9yr954r2LChEqIlYPLi3JqN8ezM=; b=MWd+hOYP/XT8JhDN37zPYJpwEJYaMjz+DGw/Gv25gw+eg0s/a5gjnsTq2fxMFRjXfa XOMVBcpP7CyWqNHbBWmey7hjHyMNnG+gxrzc/jDFOObGBsroeG0GPzJLFwCtev3yPYQp vVyxleV0C7JUqQAW22vpLbZCcIWLOpw1cxhDg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=M974k2iyDJIOjsCt9yr954r2LChEqIlYPLi3JqN8ezM=; b=kde0CtfEzr7T4AlAcbX1SMLOGt9QFv2tX4haYrsb0XDlCKuvJVICbJcQZJJe0Epgri ty/euquNtdwbMx775e/T5NU1/En2eYveEHXAMtF6nGuHoijIkPfRMpWRcYO1GLwFTjAT Ds535gEPqpjBBoMAvtNFiqZA4NjeliwC+TJRKJS79chPrGVKVx2QZa8xs+BItj+ZjPqP Y84w4bTxCXZM7BDxYveAAWOEeCLYduc3gtBWOITkw0IiUTqZuQprMz5ZMmfRWA5IyTV7 +W96atd+yKRyEJ/6B6CZWMB1rTZyKuCSB2mReAAQRkDfAnUcrqmGoM1ReUjmAaZM51Lv 8nsA== X-Gm-Message-State: ABuFfoj54PkCO0Fj5NNLsNLuVgS29J3tWxOdc/54TAOoAg74LI8Zr2nG aUVvpaM2iemUznk3PkHtwYTQ5Q== X-Google-Smtp-Source: ACcGV614x+adL4bvBW2ETzXeZ17LWqoKCU2QTWwE8UtRdZ8cX4K5Bkp1v89Z9ZQ2IkgyOmpJzyMJig== X-Received: by 2002:a1c:9901:: with SMTP id b1-v6mr4381093wme.15.1538727220155; Fri, 05 Oct 2018 01:13:40 -0700 (PDT) Received: from localhost.localdomain ([2a01:cb1d:112:6f00:697e:67d9:a05d:22c7]) by smtp.gmail.com with ESMTPSA id t4-v6sm6565620wrb.45.2018.10.05.01.13.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Oct 2018 01:13:39 -0700 (PDT) From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Subject: [RFC PATCH 1/9] kernel: add support for patchable function pointers Date: Fri, 5 Oct 2018 10:13:25 +0200 Message-Id: <20181005081333.15018-2-ard.biesheuvel@linaro.org> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20181005081333.15018-1-ard.biesheuvel@linaro.org> References: <20181005081333.15018-1-ard.biesheuvel@linaro.org> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Jason A . Donenfeld" , Peter Zijlstra , Catalin Marinas , Will Deacon , Samuel Neves , Paul Mackerras , Herbert Xu , Richard Weinberger , Eric Biggers , Ingo Molnar , Kees Cook , Arnd Bergmann , Andy Lutomirski , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, "Martin K. Petersen" , Ard Biesheuvel , Greg Kroah-Hartman , linux-crypto@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Add a function pointer abstraction that can be implemented by the arch in a manner that avoids the downsides of function pointers, i.e., the fact that they are typically located in a writable data section, and their vulnerability to Spectre like defects. The FFP (or fast function pointer) is callable as a function, since the generic incarnation is simply that. However, due to the fact that C does not distinguish between functions and function pointers at the call site, the architecture can instead emit it as a patchable sequence of instructions consisting of ordinary branches. Signed-off-by: Ard Biesheuvel --- arch/Kconfig | 3 ++ include/linux/ffp.h | 43 ++++++++++++++++++++ 2 files changed, 46 insertions(+) diff --git a/arch/Kconfig b/arch/Kconfig index 6801123932a5..2af3442a61d3 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -862,6 +862,9 @@ config HAVE_ARCH_PREL32_RELOCATIONS architectures, and don't require runtime relocation on relocatable kernels. +config HAVE_ARCH_FFP + bool + source "kernel/gcov/Kconfig" source "scripts/gcc-plugins/Kconfig" diff --git a/include/linux/ffp.h b/include/linux/ffp.h new file mode 100644 index 000000000000..8fc3b4c9b38f --- /dev/null +++ b/include/linux/ffp.h @@ -0,0 +1,43 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef __LINUX_FFP_H +#define __LINUX_FFP_H + +#include +#include + +#ifdef CONFIG_HAVE_ARCH_FFP +#include +#else + +struct ffp { + void (**fn)(void); + void (*default_fn)(void); +}; + +#define DECLARE_FFP(_fn, _def) \ + extern typeof(_def) *_fn; \ + extern struct ffp const __ffp_ ## _fn + +#define DEFINE_FFP(_fn, _def) \ + typeof(_def) *_fn = &_def; \ + struct ffp const __ffp_ ## _fn \ + = { (void(**)(void))&_fn, (void(*)(void))&_def }; \ + EXPORT_SYMBOL(__ffp_ ## _fn) + +static inline void ffp_set_target(const struct ffp *m, void *new_fn) +{ + WRITE_ONCE(*m->fn, new_fn); +} + +static inline void ffp_reset_target(const struct ffp *m) +{ + WRITE_ONCE(*m->fn, m->default_fn); +} + +#endif + +#define SET_FFP(_fn, _new) ffp_set_target(&__ffp_ ## _fn, _new) +#define RESET_FFP(_fn) ffp_reset_target(&__ffp_ ## _fn) + +#endif