From patchwork Wed Aug 21 19:49:47 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 821105 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 BB6A0137745; Wed, 21 Aug 2024 19:50:31 +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=1724269831; cv=none; b=r20LdvzZ6z+ac7/7VMMvYQ/jIbNZo/z40PeUCkm9uUmRmXH7+KQ68RSJaMnUmVzSTbxjhh3ZylCc4BXfjXeG9O5oO+PU759KfoS9yjScszJJONnN+6diK5P5+O/ntCcikkoPDIs/AUJjQIF0Jqz7b4kFPpK2nMa23XcK8mxTtWI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724269831; c=relaxed/simple; bh=XqaXLGAQ/MwY54koFKC2rQRtWZp0KxmYdMIZOGKT0R8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=dGrbjI+1iN3lCex3PyOIR/cEte5JWE5FHeUascZIGRO/8Nzj34u0NWoBoHH3rzxIiKByNDEfx9lXrxsM+ILDyEhm1dSOYZ4ogmFCuxwmUFFAYlmBPrANMg1MkjnaXT1mkYJGecFmk0kaUV4NKZWf0rowtoNMFA6ZvYmsPd4Rn5s= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WLyRI3bO; 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="WLyRI3bO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 43A13C4AF13; Wed, 21 Aug 2024 19:50:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724269831; bh=XqaXLGAQ/MwY54koFKC2rQRtWZp0KxmYdMIZOGKT0R8=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=WLyRI3bOPlN+noQ8+juXVDa0etYYSXg6Zz9bBTHAY4qvxJ48a3CSxpoOHeihFxu6g HsHu0f6joxUITmqgwweHwa471dfd1MiWY+Dc4TR3nYH7eTloUgHEHrqpl7mcgNjB/8 fcB9Hmm521oimjaXpHq5UgGQbVyx4/x2bP0V9zDc4T4irZrFsEne/zpUR80alGnG2y L20d5WBXlYLWRsOZ3fjBWWdXba7m7GP2AOzQd88vAa8zWcYslQsvho0ZhqyjQuzUgA DbjgJMP1YaLdI2m+A3ygBgTpSnowdGVG6wTQmLUVQY77PLOS6D7MOSMA0Y9nUkVjoG w/hxkd2v7AtZA== From: Mark Brown Date: Wed, 21 Aug 2024 20:49:47 +0100 Subject: [PATCH RFT v10 1/8] 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: <20240821-clone3-shadow-stack-v10-1-06e8797b9445@kernel.org> References: <20240821-clone3-shadow-stack-v10-0-06e8797b9445@kernel.org> In-Reply-To: <20240821-clone3-shadow-stack-v10-0-06e8797b9445@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-37811 X-Developer-Signature: v=1; a=openpgp-sha256; l=3025; i=broonie@kernel.org; h=from:subject:message-id; bh=XqaXLGAQ/MwY54koFKC2rQRtWZp0KxmYdMIZOGKT0R8=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBmxkTzN8r7uAOtp9K3ugTi+sHgrab9M/rfCFd5DE9G jAMkX96JATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZsZE8wAKCRAk1otyXVSH0DYUB/ sEp2EphzksK2LC6zHqb4zhg9kZ6qJZA1N/HJovcXAeYxmUl6+DyHZn6WvxUqt34GnAPYV0j5F/h6rI Nyh9GjWy4KiJvYkbTAHLAzDEdu7KllpZlGgq4ESgzHXxu89cGS1vTGKO0TC+4R9MwrZUcQINB2JoXP +GyLCZnKVWUNWyUMPx2aqPQiq/oT8R84/lOdoZT3iaiiBofBO9YfyYOhTp67oEICW3/PfublaIQOC6 61f100EOCE6ZN1ZXUwDMq+FX3DLQFW3+42uiUXfeSu9JF0qzDSFsy+NVXDJNb9Gu3WMliIpa5Q+Lga rkGhIPS857aNxfrH1rmUaaH+C53e35 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 Signed-off-by: Mark Brown --- Documentation/userspace-api/index.rst | 1 + Documentation/userspace-api/shadow_stack.rst | 41 ++++++++++++++++++++++++++++ 2 files changed, 42 insertions(+) diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index 274cc7546efc..c39709bfba2c 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -59,6 +59,7 @@ 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..c576ad3d7ec1 --- /dev/null +++ b/Documentation/userspace-api/shadow_stack.rst @@ -0,0 +1,41 @@ +============= +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() + +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.