From patchwork Thu Jun 4 13:49:53 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexander Popov X-Patchwork-Id: 11588005 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id DC0D690 for ; Thu, 4 Jun 2020 13:50:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C52D620772 for ; Thu, 4 Jun 2020 13:50:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728720AbgFDNus (ORCPT ); Thu, 4 Jun 2020 09:50:48 -0400 Received: from mail-lj1-f195.google.com ([209.85.208.195]:44327 "EHLO mail-lj1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728337AbgFDNur (ORCPT ); Thu, 4 Jun 2020 09:50:47 -0400 Received: by mail-lj1-f195.google.com with SMTP id c17so7346666lji.11; Thu, 04 Jun 2020 06:50:45 -0700 (PDT) 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:mime-version:content-transfer-encoding; bh=HscaqQ3a9rlG7LMvxfetj9PZadqBQlxA9luDvY709kI=; b=ai6pgs+Tew/uxPdpW0D6kM9fjKaFU57Yse/NujW+695tWtAZsHbMGGjsRLwvkvSFdM tKaKvGQpWjWbihXm9SM7bzwIuUyydb6gftVGfGn+rqrf8iT84i2RTj6MP76Pkb3s7Wtv u2i1GX3tx60c2Sye/K5XP1y5zvn163ycQ1SR1IDsoyjiGPkmpQ9nc5k8xIuY7cpNXkxe Ny3vMLTeLJHhVYOFYSlJMhAkaXrk7pKOBF/AP1p5BtvMyovAinP3X23oSRcwCyermoIZ OOdjYs1SLiwTCfRS0PA+Ha75IlelzNAKXJeEctRiFvw7bbdTtJSLgfapP+/Nti9yhtyg q8Nw== X-Gm-Message-State: AOAM530Fkf4utpvodap55ttY2/yNOYsu0YKEeaGDv2lW83PULYVAn2oJ 4Axxi4wbLXQjpHiWggk/vqM= X-Google-Smtp-Source: ABdhPJwFgNnX9eJFc5s+1RCeoml4wry3jADSZr+Uk82Gr4M4947yFLD4wkmGdf/0gl0X9+wHhybHLA== X-Received: by 2002:a2e:8ec9:: with SMTP id e9mr2378478ljl.152.1591278644807; Thu, 04 Jun 2020 06:50:44 -0700 (PDT) Received: from localhost.localdomain ([185.248.161.177]) by smtp.gmail.com with ESMTPSA id u16sm1202140lji.58.2020.06.04.06.50.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Jun 2020 06:50:43 -0700 (PDT) From: Alexander Popov To: Kees Cook , Emese Revfy , Miguel Ojeda , Masahiro Yamada , Michal Marek , Andrew Morton , Masahiro Yamada , Thiago Jung Bauermann , Luis Chamberlain , Jessica Yu , Sven Schnelle , Iurii Zaikin , Catalin Marinas , Will Deacon , Vincenzo Frascino , Thomas Gleixner , Peter Collingbourne , Naohiro Aota , Alexander Monakov , Mathias Krause , PaX Team , Brad Spengler , Laura Abbott , Florian Weimer , Alexander Popov , kernel-hardening@lists.openwall.com, linux-kbuild@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, gcc@gcc.gnu.org Cc: notify@kernel.org Subject: [PATCH 1/5] gcc-plugins/stackleak: Exclude alloca() from the instrumentation logic Date: Thu, 4 Jun 2020 16:49:53 +0300 Message-Id: <20200604134957.505389-2-alex.popov@linux.com> X-Mailer: git-send-email 2.25.2 In-Reply-To: <20200604134957.505389-1-alex.popov@linux.com> References: <20200604134957.505389-1-alex.popov@linux.com> MIME-Version: 1.0 Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org Some time ago Variable Length Arrays (VLA) were removed from the kernel. The kernel is built with '-Wvla'. Let's exclude alloca() from the instrumentation logic and make it simpler. The build-time assertion against alloca() is added instead. Unfortunately, for that assertion we can't simply check cfun->calls_alloca during RTL phase. It turned out that gcc before version 7 called allocate_dynamic_stack_space() from expand_stack_vars() for runtime alignment of constant-sized stack variables. That caused cfun->calls_alloca to be set for functions that don't use alloca(). Signed-off-by: Alexander Popov --- scripts/gcc-plugins/stackleak_plugin.c | 51 +++++++++++--------------- 1 file changed, 21 insertions(+), 30 deletions(-) diff --git a/scripts/gcc-plugins/stackleak_plugin.c b/scripts/gcc-plugins/stackleak_plugin.c index cc75eeba0be1..1ecfe50d0bf5 100644 --- a/scripts/gcc-plugins/stackleak_plugin.c +++ b/scripts/gcc-plugins/stackleak_plugin.c @@ -9,10 +9,9 @@ * any of the gcc libraries * * This gcc plugin is needed for tracking the lowest border of the kernel stack. - * It instruments the kernel code inserting stackleak_track_stack() calls: - * - after alloca(); - * - for the functions with a stack frame size greater than or equal - * to the "track-min-size" plugin parameter. + * It instruments the kernel code inserting stackleak_track_stack() calls + * for the functions with a stack frame size greater than or equal to + * the "track-min-size" plugin parameter. * * This plugin is ported from grsecurity/PaX. For more information see: * https://grsecurity.net/ @@ -46,7 +45,7 @@ static struct plugin_info stackleak_plugin_info = { "disable\t\tdo not activate the plugin\n" }; -static void stackleak_add_track_stack(gimple_stmt_iterator *gsi, bool after) +static void stackleak_add_track_stack(gimple_stmt_iterator *gsi) { gimple stmt; gcall *stackleak_track_stack; @@ -56,12 +55,7 @@ static void stackleak_add_track_stack(gimple_stmt_iterator *gsi, bool after) /* Insert call to void stackleak_track_stack(void) */ stmt = gimple_build_call(track_function_decl, 0); stackleak_track_stack = as_a_gcall(stmt); - if (after) { - gsi_insert_after(gsi, stackleak_track_stack, - GSI_CONTINUE_LINKING); - } else { - gsi_insert_before(gsi, stackleak_track_stack, GSI_SAME_STMT); - } + gsi_insert_before(gsi, stackleak_track_stack, GSI_SAME_STMT); /* Update the cgraph */ bb = gimple_bb(stackleak_track_stack); @@ -87,14 +81,13 @@ static bool is_alloca(gimple stmt) /* * Work with the GIMPLE representation of the code. Insert the - * stackleak_track_stack() call after alloca() and into the beginning - * of the function if it is not instrumented. + * stackleak_track_stack() call into the beginning of the function. */ static unsigned int stackleak_instrument_execute(void) { basic_block bb, entry_bb; - bool prologue_instrumented = false, is_leaf = true; - gimple_stmt_iterator gsi; + bool is_leaf = true; + gimple_stmt_iterator gsi = { 0 }; /* * ENTRY_BLOCK_PTR is a basic block which represents possible entry @@ -111,27 +104,17 @@ static unsigned int stackleak_instrument_execute(void) */ FOR_EACH_BB_FN(bb, cfun) { for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { - gimple stmt; - - stmt = gsi_stmt(gsi); + gimple stmt = gsi_stmt(gsi); /* Leaf function is a function which makes no calls */ if (is_gimple_call(stmt)) is_leaf = false; - if (!is_alloca(stmt)) - continue; - - /* Insert stackleak_track_stack() call after alloca() */ - stackleak_add_track_stack(&gsi, true); - if (bb == entry_bb) - prologue_instrumented = true; + /* Variable Length Arrays are forbidden in the kernel */ + gcc_assert(!is_alloca(stmt)); } } - if (prologue_instrumented) - return 0; - /* * Special cases to skip the instrumentation. * @@ -168,7 +151,7 @@ static unsigned int stackleak_instrument_execute(void) bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); } gsi = gsi_after_labels(bb); - stackleak_add_track_stack(&gsi, false); + stackleak_add_track_stack(&gsi); return 0; } @@ -185,12 +168,20 @@ static bool large_stack_frame(void) /* * Work with the RTL representation of the code. * Remove the unneeded stackleak_track_stack() calls from the functions - * which don't call alloca() and don't have a large enough stack frame size. + * that don't have a large enough stack frame size. */ static unsigned int stackleak_cleanup_execute(void) { rtx_insn *insn, *next; + /* + * gcc before version 7 called allocate_dynamic_stack_space() from + * expand_stack_vars() for runtime alignment of constant-sized stack + * variables. That caused cfun->calls_alloca to be set for functions + * that don't use alloca(). + * For more info see gcc commit 7072df0aae0c59ae437e. + * Let's leave such functions instrumented. + */ if (cfun->calls_alloca) return 0;