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=-10.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_GIT 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 E5CC8C433DF for ; Tue, 16 Jun 2020 18:36:47 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BB03B208B3 for ; Tue, 16 Jun 2020 18:36:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="lUyYXRWR"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="b8cjVnkG" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB03B208B3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:Message-Id:Date:Subject:To :From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References: List-Owner; bh=aFNV8ZgMDamNaOvq/taWEsXo/S00rMLYlodaq7OAZrU=; b=lUyYXRWRl5w7Rk F96fyqw0kVzbinSdGpI+/W1thNnW6bE9DycLpibnvzOKkqRcZbt4nkPLcXs2+bNNeVbw+vZ8EulQ/ m+O150xnQejP/6Zawny8EzPC8NryypqqCM0z/svFgI94iqiDpyvtB5uVK8yT6AOZDstAp48+l8zR2 EuoPrzpXSLGls8qBFIT/YRRo2IXtp/eeTbQUfJH23Emb8aEuEYnBYAfk5+2NeL7OoPcNqEqORWkL3 S9PoTOgYDuAzzEI2Q+byryw2aRZ/gR0ZmufpV6nBqouwWHQUaNuN1yeTn69xfnk2MaS81nMjSMwLG lvduEqiN1O0WQVrD9vsQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jlGRu-0001nE-6e; Tue, 16 Jun 2020 18:36:42 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jlGRq-0001lF-AP for linux-arm-kernel@lists.infradead.org; Tue, 16 Jun 2020 18:36:39 +0000 Received: from localhost.localdomain (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 66A05207C4; Tue, 16 Jun 2020 18:36:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592332598; bh=4NzNIX9HpS79xTiQ0dWJDWJ8fa1+r0RJ3XXw3mKE4+0=; h=From:To:Cc:Subject:Date:From; b=b8cjVnkGi+Nb+GQYbtzTmvsCmArAqwJMFfgbV2q+CYt16T8UREQ9y+N5y0wFM/2fE KgtUogwVjKOYblphCVict1gOPpKxXIkTsZCmjYzJNNrXTsIw/4q1fsivNWT7TvTZtx KQnhl0xvYe/mwWV/DJutrI/cbe9wK9Ibeq64TD70= From: Will Deacon To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] arm64: bti: Require clang >= 10.0.1 for in-kernel BTI support Date: Tue, 16 Jun 2020 19:36:30 +0100 Message-Id: <20200616183630.2445-1-will@kernel.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200616_113638_402339_7156B29D X-CRM114-Status: GOOD ( 11.17 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tom Stellard , Will Deacon , Nick Desaulniers , clang-built-linux@googlegroups.com, Mark Brown , Nathan Chancellor , kernel-team@android.com, Daniel Kiss Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Unfortunately, most versions of clang that support BTI are capable of miscompiling the kernel when converting a switch statement into a jump table. As an example, attempting to spawn a KVM guest results in a panic: [ 56.253312] Kernel panic - not syncing: bad mode [ 56.253834] CPU: 0 PID: 279 Comm: lkvm Not tainted 5.8.0-rc1 #2 [ 56.254225] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015 [ 56.254712] Call trace: [ 56.254952] dump_backtrace+0x0/0x1d4 [ 56.255305] show_stack+0x1c/0x28 [ 56.255647] dump_stack+0xc4/0x128 [ 56.255905] panic+0x16c/0x35c [ 56.256146] bad_el0_sync+0x0/0x58 [ 56.256403] el1_sync_handler+0xb4/0xe0 [ 56.256674] el1_sync+0x7c/0x100 [ 56.256928] kvm_vm_ioctl_check_extension_generic+0x74/0x98 [ 56.257286] __arm64_sys_ioctl+0x94/0xcc [ 56.257569] el0_svc_common+0x9c/0x150 [ 56.257836] do_el0_svc+0x84/0x90 [ 56.258083] el0_sync_handler+0xf8/0x298 [ 56.258361] el0_sync+0x158/0x180 This is because the switch in kvm_vm_ioctl_check_extension_generic() is executed as an indirect branch to tail-call through a jump table: ffff800010032dc8: 3869694c ldrb w12, [x10, x9] ffff800010032dcc: 8b0c096b add x11, x11, x12, lsl #2 ffff800010032dd0: d61f0160 br x11 However, where the target case uses the stack, the landing pad is elided due to the presence of a paciasp instruction: ffff800010032e14: d503233f paciasp ffff800010032e18: a9bf7bfd stp x29, x30, [sp, #-16]! ffff800010032e1c: 910003fd mov x29, sp ffff800010032e20: aa0803e0 mov x0, x8 ffff800010032e24: 940017c0 bl ffff800010038d24 ffff800010032e28: 93407c00 sxtw x0, w0 ffff800010032e2c: a8c17bfd ldp x29, x30, [sp], #16 ffff800010032e30: d50323bf autiasp ffff800010032e34: d65f03c0 ret Unfortunately, this results in a fatal exception because paciasp is compatible only with branch-and-link (call) instructions and not simple indirect branches. A fix is being merged into Clang 10.0.1 so that a 'bti j' instruction is emitted as an explicit landing pad in this situation. Make in-kernel BTI depend on that compiler version when building with clang. Cc: Nick Desaulniers Cc: Mark Brown Cc: Nathan Chancellor Cc: Tom Stellard Cc: Daniel Kiss Link: https://lore.kernel.org/r/20200615105524.GA2694@willie-the-truck Signed-off-by: Will Deacon --- arch/arm64/Kconfig | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 31380da53689..4ae2419c14a8 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1630,6 +1630,8 @@ config ARM64_BTI_KERNEL depends on CC_HAS_BRANCH_PROT_PAC_RET_BTI # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94697 depends on !CC_IS_GCC || GCC_VERSION >= 100100 + # https://reviews.llvm.org/rGb8ae3fdfa579dbf366b1bb1cbfdbf8c51db7fa55 + depends on !CC_IS_CLANG || CLANG_VERSION >= 100001 depends on !(CC_IS_CLANG && GCOV_KERNEL) depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS) help -- 2.27.0.290.gba653c62da-goog _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel