From patchwork Tue Aug 22 13:56:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 13360849 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B27A5EE49AE for ; Tue, 22 Aug 2023 14:07:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236508AbjHVOHO (ORCPT ); Tue, 22 Aug 2023 10:07:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39116 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236499AbjHVOHM (ORCPT ); Tue, 22 Aug 2023 10:07:12 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A40C10C0; Tue, 22 Aug 2023 07:06:44 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1B82C6572D; Tue, 22 Aug 2023 14:05:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A035FC433C9; Tue, 22 Aug 2023 14:05:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692713113; bh=wOX/VCidy7u5iRp7jBzI1P7kDYiqBOUXs9IWPVUSObE=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=apmSXf70i+L2CfCRz42YhP1pkXCBW8zxOoSAszXGPD6JyVqTj0ly+IxPBY5nE/2yS pneznh6M4XSaoTsMNELVPJL/XORyPibcdwVz5zCz4cE7Ut6tu2oD2FGaxtO01/juGa 0AndYXALyRcMZhtNeBxpzmvYkNkKt4u6AhaJYnjLGYbzGiZ6mKHhT2G5gbw3B/Ox9A cnmaX3vyQF2cmcvZ9zrn/lRVXZh8Zg52hFtIMJlYWk0TZGYGMQGFBs2sPSwOBi3vAw SK9vHl5fi+0PimT2GL2p2hVG05NLnQw24S1wUzBMZmIz6hZA17A2HMrQj0gc+lDHQu qqIPHOS3f5S0w== From: Mark Brown Date: Tue, 22 Aug 2023 14:56:54 +0100 Subject: [PATCH v5 21/37] arm64/gcs: Implement shadow stack prctl() interface MIME-Version: 1.0 Message-Id: <20230822-arm64-gcs-v5-21-9ef181dd6324@kernel.org> References: <20230822-arm64-gcs-v5-0-9ef181dd6324@kernel.org> In-Reply-To: <20230822-arm64-gcs-v5-0-9ef181dd6324@kernel.org> To: Catalin Marinas , Will Deacon , Jonathan Corbet , Andrew Morton , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Arnd Bergmann , Oleg Nesterov , Eric Biederman , Kees Cook , Shuah Khan , "Rick P. Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy Cc: "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Mark Brown X-Mailer: b4 0.13-dev-034f2 X-Developer-Signature: v=1; a=openpgp-sha256; l=5673; i=broonie@kernel.org; h=from:subject:message-id; bh=wOX/VCidy7u5iRp7jBzI1P7kDYiqBOUXs9IWPVUSObE=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBk5MAA2xXU0yOlZuLfjAjUHXBIFEmNGeUAu5yPZAcb hB8xI5mJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZOTAAAAKCRAk1otyXVSH0JrtB/ 9wcNsUF8PghBmNZpEF7fn73il0mXg+vUlQy+1+X2sjHfJLltiZBoSsDu07/any1RTGyLgpQGTl3C2S Ns3AQV03nr6RqnTNSnxUeYrbtTsAJjq+lV/f72XH2eLjA74KWQ2xKYj1nZ9+BqetsMWZQF2Mc80Vln d8RXI07c4O5cGMYoW3uvvkYHAHVpTAlXXDv+xpTIvTtSS2p9zIEdk611xwk2FAZV5E1zXMYkWrmtdh DzVpkMZcbHMD6BvC5JBpF9lP9sJfTe7dw3S5qsIrfZKqJmFt1DoVi1+g0pp55+ranSbsRgYZyDgULE euQstx5ph7QA8i6DtFq28FcNRG86QU X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Implement the architecture neutral prtctl() interface for setting the shadow stack status, this supports setting and reading the current GCS configuration for the current thread. Userspace can enable basic GCS functionality and additionally also support for GCS pushes and arbatrary GCS stores. It is expected that this prctl() will be called very early in application startup, for example by the dynamic linker, and not subsequently adjusted during normal operation. Users should carefully note that after enabling GCS for a thread GCS will become active with no call stack so it is not normally possible to return from the function that invoked the prctl(). State is stored per thread, enabling GCS for a thread causes a GCS to be allocated for that thread. Userspace may lock the current GCS configuration by specifying PR_SHADOW_STACK_ENABLE_LOCK, this prevents any further changes to the GCS configuration via any means. If GCS is not being enabled then all flags other than _LOCK are ignored, it is not possible to enable stores or pops without enabling GCS. When disabling the GCS we do not free the allocated stack, this allows for inspection of the GCS after disabling as part of fault reporting. Since it is not an expected use case and since it presents some complications in determining what to do with previously initialsed data on the GCS attempts to reenable GCS after this are rejected. This can be revisted if a use case arises. Signed-off-by: Mark Brown --- arch/arm64/include/asm/gcs.h | 22 ++++++++++ arch/arm64/include/asm/processor.h | 1 + arch/arm64/mm/gcs.c | 82 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 105 insertions(+) diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h index 4371a2f99b4a..c150e76869a1 100644 --- a/arch/arm64/include/asm/gcs.h +++ b/arch/arm64/include/asm/gcs.h @@ -48,6 +48,9 @@ static inline u64 gcsss2(void) return Xt; } +#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK \ + (PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE | PR_SHADOW_STACK_PUSH) + #ifdef CONFIG_ARM64_GCS static inline bool task_gcs_el0_enabled(struct task_struct *task) @@ -61,6 +64,20 @@ void gcs_preserve_current_state(void); unsigned long gcs_alloc_thread_stack(struct task_struct *tsk, unsigned long clone_flags, size_t size); +static inline int gcs_check_locked(struct task_struct *task, + unsigned long new_val) +{ + unsigned long cur_val = task->thread.gcs_el0_mode; + + cur_val &= task->thread.gcs_el0_locked; + new_val &= task->thread.gcs_el0_locked; + + if (cur_val != new_val) + return -EBUSY; + + return 0; +} + #else static inline bool task_gcs_el0_enabled(struct task_struct *task) @@ -76,6 +93,11 @@ static inline unsigned long gcs_alloc_thread_stack(struct task_struct *tsk, { return -ENOTSUPP; } +static inline int gcs_check_locked(struct task_struct *task, + unsigned long new_val) +{ + return 0; +} #endif diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index c28681cf9721..029d20ea7878 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -181,6 +181,7 @@ struct thread_struct { u64 tpidr2_el0; #ifdef CONFIG_ARM64_GCS unsigned int gcs_el0_mode; + unsigned int gcs_el0_locked; u64 gcspr_el0; u64 gcs_base; u64 gcs_size; diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c index cb0a64bf90af..2b2223b13fc3 100644 --- a/arch/arm64/mm/gcs.c +++ b/arch/arm64/mm/gcs.c @@ -84,3 +84,85 @@ void gcs_free(struct task_struct *task) task->thread.gcs_base = 0; task->thread.gcs_size = 0; } + +int arch_set_shadow_stack_status(struct task_struct *task, unsigned long arg) +{ + unsigned long gcs, size; + int ret; + + if (!system_supports_gcs()) + return -EINVAL; + + if (is_compat_thread(task_thread_info(task))) + return -EINVAL; + + /* Reject unknown flags */ + if (arg & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK) + return -EINVAL; + + ret = gcs_check_locked(task, arg); + if (ret != 0) + return ret; + + /* If we are enabling GCS then make sure we have a stack */ + if (arg & PR_SHADOW_STACK_ENABLE) { + if (!task_gcs_el0_enabled(task)) { + /* Do not allow GCS to be reenabled */ + if (task->thread.gcs_base) + return -EINVAL; + + if (task != current) + return -EBUSY; + + size = gcs_size(0); + gcs = alloc_gcs(task->thread.gcspr_el0, size, + 0, 0); + if (!gcs) + return -ENOMEM; + + task->thread.gcspr_el0 = gcs + size - sizeof(u64); + task->thread.gcs_base = gcs; + task->thread.gcs_size = size; + if (task == current) + write_sysreg_s(task->thread.gcspr_el0, + SYS_GCSPR_EL0); + + } + } + + task->thread.gcs_el0_mode = arg; + if (task == current) + gcs_set_el0_mode(task); + + return 0; +} + +int arch_get_shadow_stack_status(struct task_struct *task, + unsigned long __user *arg) +{ + if (!system_supports_gcs()) + return -EINVAL; + + if (is_compat_thread(task_thread_info(task))) + return -EINVAL; + + return put_user(task->thread.gcs_el0_mode, arg); +} + +int arch_lock_shadow_stack_status(struct task_struct *task, + unsigned long arg) +{ + if (!system_supports_gcs()) + return -EINVAL; + + if (is_compat_thread(task_thread_info(task))) + return -EINVAL; + + /* + * We support locking unknown bits so applications can prevent + * any changes in a future proof manner. + */ + task->thread.gcs_el0_locked |= arg; + + return 0; +}