From patchwork Tue Apr 8 18:49:42 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 879208 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 C23F2241678; Tue, 8 Apr 2025 18:50:39 +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=1744138239; cv=none; b=VoGBSa/CS1XOwT7IbdLZNdmMx2jEUuny4pZ8JEayMBxk3/DKdukfiYpPyOZYO9cRvHwZjei3l8xdMGWiHG6lUBW0WWrrj0J3C8E/J8p4yAtJZxJLPGgjdTNd1WLNw5yi/QPpLbWOIRPLhuaS18wIoU3AdN64wYJXD23Nv2ANrh8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744138239; c=relaxed/simple; bh=k56u8xsssiS9PLGw09HLQ5Vh+FXmTGCSWgKOA+mivOY=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=Q0VkBt7RGza3BkCPc3yhXILFcb/L91AI8TcB+ueXyWkFyhId4uvWVH4l2ftGl24ST/BHGubcwbkMqKoI+izPELobntw9vTQq2KvXPYVjNOh3Fgey26+t2WVhk9i5zwcf2wjGdSy+tSdmgzcYD5x9pu57A1qdVgxPVARsN4Q6lGY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=J0X8XZX6; 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="J0X8XZX6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 99D33C4CEE8; Tue, 8 Apr 2025 18:50:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744138239; bh=k56u8xsssiS9PLGw09HLQ5Vh+FXmTGCSWgKOA+mivOY=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=J0X8XZX61BVSHHOroz19lUhgfLNDjFWUqoEPUHRgjq7sZRsryzbd14wW/jwSyu9oQ F4kPGG9RJMWhIB6s3A/ZH2dJKpSJdZcBuewmrtk4iwPyDIoA8ExigjWRcst/gNymy5 Z9cBRUxvj5pTjyT1HdsVbFAjCUIjiizr6EwCywmt2oAOBj5sQLxegdg/2LJXqBoe5j z3f8f4Z2w7hWIZYB/K7pyguqXr5cdvQKAZcNrhQC2fwVO5SjJMmxYFa41P7aMnCsgM OyiJCJasBL5miT4eBoFJdb/ngL4MHeDwDh02f6pGYsfHccJIQYJI8j+WUlS5eZCU7Z R2z9k9BbeOpmA== From: Mark Brown Date: Tue, 08 Apr 2025 19:49:42 +0100 Subject: [PATCH RFT v15 2/8] Documentation: userspace-api: Add shadow stack API documentation Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20250408-clone3-shadow-stack-v15-2-3fa245c6e3be@kernel.org> References: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@kernel.org> In-Reply-To: <20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@kernel.org> To: "Rick P. Edgecombe" , Deepak Gupta , Szabolcs Nagy , "H.J. Lu" , Florian Weimer , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Christian Brauner , Shuah Khan Cc: linux-kernel@vger.kernel.org, Catalin Marinas , Will Deacon , jannh@google.com, bsegall@google.com, Yury Khrustalev , Wilco Dijkstra , linux-kselftest@vger.kernel.org, linux-api@vger.kernel.org, Mark Brown , Kees Cook , Kees Cook , Shuah Khan X-Mailer: b4 0.15-dev-c25d1 X-Developer-Signature: v=1; a=openpgp-sha256; l=3235; i=broonie@kernel.org; h=from:subject:message-id; bh=k56u8xsssiS9PLGw09HLQ5Vh+FXmTGCSWgKOA+mivOY=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBn9W/ooniTARt6/JF4hCBA0D+hWJCBXdE+dR3uxruN RVcDO7uJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZ/Vv6AAKCRAk1otyXVSH0OO1B/ 9Srn6gXti+dRcHL9KQNBljGQUtUQRC2oVqUsr/DjwQo0+mm6HdNnrMT3HLRZklF/1XLe0cS+h2koMF +UGWiuriCRQqyffiIA4wGW7KpxvGd7hESCAwmQ/C7mhQpisDaJZt1XJiXuj8bofn1kqzrzIHvTfHm6 U8NlJGDWYbc9BXJKMJMkg5jRTgPPJwztgog8l2m02J9mJScJBLkwfRDRrETpKRuk/dX/Pqc4K54WFh OWF86/phmJPUitNJXumc68mYfXhSMecwScRFCjWWYTMiLdHpRPu22riHXQ1e1+9LOVhXPKrF7+slw3 fljMC7En+Qif/nkg+9qT2lYvbyx3Xu X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB There are a number of architectures with shadow stack features which we are presenting to userspace with as consistent an API as we can (though there are some architecture specifics). Especially given that there are some important considerations for userspace code interacting directly with the feature let's provide some documentation covering the common aspects. Reviewed-by: Catalin Marinas Reviewed-by: Kees Cook Tested-by: Kees Cook Acked-by: Shuah Khan Acked-by: Yury Khrustalev Reviewed-by: Deepak Gupta Signed-off-by: Mark Brown --- Documentation/userspace-api/index.rst | 1 + Documentation/userspace-api/shadow_stack.rst | 44 ++++++++++++++++++++++++++++ 2 files changed, 45 insertions(+) diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index b8c73be4fb11..0167e59b541e 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -62,6 +62,7 @@ Everything else ELF netlink/index + shadow_stack sysfs-platform_profile vduse futex2 diff --git a/Documentation/userspace-api/shadow_stack.rst b/Documentation/userspace-api/shadow_stack.rst new file mode 100644 index 000000000000..65c665496624 --- /dev/null +++ b/Documentation/userspace-api/shadow_stack.rst @@ -0,0 +1,44 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============= +Shadow Stacks +============= + +Introduction +============ + +Several architectures have features which provide backward edge +control flow protection through a hardware maintained stack, only +writeable by userspace through very limited operations. This feature +is referred to as shadow stacks on Linux, on x86 it is part of Intel +Control Enforcement Technology (CET), on arm64 it is Guarded Control +Stacks feature (FEAT_GCS) and for RISC-V it is the Zicfiss extension. +It is expected that this feature will normally be managed by the +system dynamic linker and libc in ways broadly transparent to +application code, this document covers interfaces and considerations. + + +Enabling +======== + +Shadow stacks default to disabled when a userspace process is +executed, they can be enabled for the current thread with a syscall: + + - For x86 the ARCH_SHSTK_ENABLE arch_prctl() + - For other architectures the PR_SET_SHADOW_STACK_ENABLE prctl() + +It is expected that this will normally be done by the dynamic linker. +Any new threads created by a thread with shadow stacks enabled will +themselves have shadow stacks enabled. + + +Enablement considerations +========================= + +- Returning from the function that enables shadow stacks without first + disabling them will cause a shadow stack exception. This includes + any syscall wrapper or other library functions, the syscall will need + to be inlined. +- A lock feature allows userspace to prevent disabling of shadow stacks. +- Those that change the stack context like longjmp() or use of ucontext + changes on signal return will need support from libc.