From nobody Mon Nov 25 01:37:51 2024 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 4CC021C9DD5; Thu, 31 Oct 2024 19:25:47 +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=1730402747; cv=none; b=FVokmlcSxme8F7EpoL0g7ADDhYctPYXabCmBD8rV1xHb0TKUsx5sDfVTwHn2Nl9yGAn5DjKcsxAbvre/4ibeDk23TTGFoFxeSgXEIrQyYDRuJEqIA7AAkWiUznkZT8QuHvDKv9ioRj7eThWFhzn+7Dvo0HkmcDdxF9Tbx7PPQi8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730402747; c=relaxed/simple; bh=AbLth5zSxZKGDmgHKpPb77+q+UuyNvYPAoJ2d927a7g=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=t8M8U+vC578zEoTmmClvYt75Ym3yBujh9ePxngE+uqVsqkS0bfv8TFG4/XbK3vCaAQOH0ny5+PJNXoWU27sWSwPbJBlriaJYG07we7GUwZmJ/Yk9qck0jIj06Q6sxd15sYDlALOLOUC+PX0OrgbMD93ZQRqu6tGVMr6pbbYsVpk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tTRYES7U; 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="tTRYES7U" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29938C4CED5; Thu, 31 Oct 2024 19:25:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1730402746; bh=AbLth5zSxZKGDmgHKpPb77+q+UuyNvYPAoJ2d927a7g=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=tTRYES7UjaIysSzme+hY4ndfmiYPIZcR65Y8CjQG4I2ww4mdabaEU7gdECXUYYPOR DUh7gDbKapImKeU0ayma9XLL0+eaj4bcF24yxrfXhSapmlSz8R9fjI0LotBUNQcOxO Qex/HhjW6hJ5CX9LxCoGcb+znwWDukb1IbSJ+tjtJRo+puVUOu4qp2PmlH1H/cFIOH ujq7jynMZXc5J9afn+wxQaMSpdZn9KHh13uCvwTHpBgfRx2WDud4XfmARH1aGU04+f bR4wFGMchPnyAswN4XBxB/s5IMdCf29KnqxSwGuVMUi6zLmw5+pUIiXOoE/ibZ3RLw VG/rq79CPAQFQ== From: Mark Brown Date: Thu, 31 Oct 2024 19:25:03 +0000 Subject: [PATCH RFT v12 2/8] Documentation: userspace-api: Add shadow stack API documentation Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20241031-clone3-shadow-stack-v12-2-7183eb8bee17@kernel.org> References: <20241031-clone3-shadow-stack-v12-0-7183eb8bee17@kernel.org> In-Reply-To: <20241031-clone3-shadow-stack-v12-0-7183eb8bee17@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-9b746 X-Developer-Signature: v=1; a=openpgp-sha256; l=3205; i=broonie@kernel.org; h=from:subject:message-id; bh=AbLth5zSxZKGDmgHKpPb77+q+UuyNvYPAoJ2d927a7g=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBnI9mjcYzJgOXqROdCTV6U13+vds446fSmpbnSYa26 K5EHJFqJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZyPZowAKCRAk1otyXVSH0HfOB/ 9JoESZWcg/BurSCzknvzkNSxSB1EUcIoa6UZobO1DtjeccIofJvAEEb3hzO9z0Bm669tdO3Xlympn5 QCwRDXFHfYjrsdA7o46ttv2hKOwMn62mdUMp/b3y3ufByOJyYcSfX3O828IIrGjKDlnOTfQ7hYO7uH cw3+QBUru94Krhx+LX+o5deIG4lylgJ1p9EOpacIieJypNUHokn3cLBzPQQA8qmfQy+yAGAsHqLy/t zSQ9hA69tykd7Ji6zl70fLo44z5NdyeP8y1QE1IyasH+yeWHoaJu/zY/dN4NYiVQNR+YeLCUJWYYnh uSdWbt8UG/LEKo4LqEApfbfBI3IZrP 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 | 42 ++++++++++++++++++++++++= ++++ 2 files changed, 43 insertions(+) diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspac= e-api/index.rst index 274cc7546efc2a042d2dc00aa67c71c52372179a..c39709bfba2c5682d0d1a22444d= b17c17bcf01ce 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -59,6 +59,7 @@ Everything else =20 ELF netlink/index + shadow_stack sysfs-platform_profile vduse futex2 diff --git a/Documentation/userspace-api/shadow_stack.rst b/Documentation/u= serspace-api/shadow_stack.rst new file mode 100644 index 0000000000000000000000000000000000000000..9d0d4e79cfa7c47d3208dd53071= a3d0b86c18575 --- /dev/null +++ b/Documentation/userspace-api/shadow_stack.rst @@ -0,0 +1,42 @@ +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Shadow Stacks +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +Introduction +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +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 +=3D=3D=3D=3D=3D=3D=3D=3D + +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 +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D + +- 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. --=20 2.39.2