From patchwork Tue Oct 1 22:59:02 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 13818896 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9DD681CEEB4; Tue, 1 Oct 2024 23:04:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727823855; cv=none; b=UpamlQ97PB2lAjjEv+6wPAeJg/fVa9bRHQooLWhBtS9K+vK+qLv0CCor+lFyh4uoQdwgckjPbdBr5KxQZ1PzH59LQFyFXB5iJ7wOob4c/civ9wipcIQ4IGoekdN8CnC61GX7OfhpNVmCF1njDsoL/3ysQPoPqDc0Dq6pjjquAgU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727823855; c=relaxed/simple; bh=K+4cP/LC+6mSpPudlQELRYVPS4rd6r8ORRNSqB8UjUA=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=h1mKg26InbEacbtY4/YavDSPhU1P2PDuPBYHbcbP/9G84+reuwIEbR22rLC+mLF5TLNaF2VJStpJD1PDU3OXzyM/PuZ/LrLI+j++ylMzJ3xHSVI8LJ1KVrXGpKrtxzn4y/ZWG7qBY44/4Jtcy3YCrjOrYfx4n9I/UkXW9lKMqek= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=o2MdUGnL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="o2MdUGnL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2726EC4CECF; Tue, 1 Oct 2024 23:04:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1727823855; bh=K+4cP/LC+6mSpPudlQELRYVPS4rd6r8ORRNSqB8UjUA=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=o2MdUGnL5Lkyqt2enbopAP49L/70lDvxYky74Nl0WWhMGq9vjYnXGZIcyw0hh/sZd RxJu6+suVH8ko3sabz6JhGs0pEeA+aanTJ8lYnZvj2kSCXNLgey1QekFyDd276iJ9N KPQIz/bYmk19enHpAY1tcPo/BNtbSeaW2RVKcLK2KvaEjx0r3B9bHxCXfqpVBAop0n 3/U5+yMuBzw/iEKSZk5sSmktiIroD5o9TCK+8O8hXKz/pPOf0XEUv7nGKFsucd1JYs SF8tQW3CNAkNhFYttWnZlwSHvHyu2iq9ZHwHooJWUb6T7Mo1nKPJYOLV2oOFEiIfkA i5VnsWbuenqWg== From: Mark Brown Date: Tue, 01 Oct 2024 23:59:02 +0100 Subject: [PATCH v13 23/40] arm64/gcs: Implement shadow stack prctl() interface Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20241001-arm64-gcs-v13-23-222b78d87eee@kernel.org> References: <20241001-arm64-gcs-v13-0-222b78d87eee@kernel.org> In-Reply-To: <20241001-arm64-gcs-v13-0-222b78d87eee@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 , Shuah Khan , "Rick P. Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy , Kees Cook Cc: "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Florian Weimer , Christian Brauner , Thiago Jung Bauermann , Ross Burton , David Spickett , Yury Khrustalev , Wilco Dijkstra , 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 0.15-dev-99b12 X-Developer-Signature: v=1; a=openpgp-sha256; l=5761; i=broonie@kernel.org; h=from:subject:message-id; bh=K+4cP/LC+6mSpPudlQELRYVPS4rd6r8ORRNSqB8UjUA=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBm/H7WUpExgul0bhrpNsGlDL0f/qGPfOCRWKfz+rzP vEj/sFyJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZvx+1gAKCRAk1otyXVSH0KTRB/ 4vn5W6BK7wfWSlXlLbrZGTH6b8/hgaY2L9aJcWxYBTA/w4eESQ7VqP8+UbxEuN70z2NCTelIwZTyn5 8VD3B4Fn6StA+TGyhfLrZd2dcRfDmMp6az4kLJJGBMXarDDSyCqBhEv/RHKvcR0oWVmn7eSDwttVF6 6/RL4IQo83mmYZ1G2WfDyNdp8KCzrudw4N/IYc+INPoExf1b0gBE/umZRq39kPmliwYPzBEpNFtHzj +ze0oCURedGsPe8G+vq6ZnMhN6NmHXxUv3E21n6OQr8Qnxecq5rEtBtNaxfpqIipuA7zTPZvCoGXGp C5X64Qv6fSSkY3iWNtk+LwalWQVtp0 X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB Implement the architecture neutral prctl() 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 arbitrary 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. Reviewed-by: Thiago Jung Bauermann Reviewed-by: Catalin Marinas Signed-off-by: Mark Brown --- arch/arm64/include/asm/gcs.h | 22 +++++++++++ arch/arm64/include/asm/processor.h | 1 + arch/arm64/mm/gcs.c | 79 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 102 insertions(+) diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h index c1f274fdb9c0..48c97e63e56a 100644 --- a/arch/arm64/include/asm/gcs.h +++ b/arch/arm64/include/asm/gcs.h @@ -50,6 +50,9 @@ 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) @@ -63,6 +66,20 @@ void gcs_preserve_current_state(void); unsigned long gcs_alloc_thread_stack(struct task_struct *tsk, const struct kernel_clone_args *args); +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) @@ -78,6 +95,11 @@ 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 5260788247d8..37fefdc3d3a3 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -187,6 +187,7 @@ struct thread_struct { u64 por_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 3c7a18f57ea9..61a80de6baf8 100644 --- a/arch/arm64/mm/gcs.c +++ b/arch/arm64/mm/gcs.c @@ -109,3 +109,82 @@ 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 && + !task_gcs_el0_enabled(task)) { + /* Do not allow GCS to be reenabled */ + if (task->thread.gcs_base || task->thread.gcspr_el0) + return -EINVAL; + + if (task != current) + return -EBUSY; + + size = gcs_size(0); + gcs = alloc_gcs(0, size); + 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; +}