From patchwork Thu Aug 1 12:06:32 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 13750384 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E70ABC52D54 for ; Thu, 1 Aug 2024 12:58:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 808356B009F; Thu, 1 Aug 2024 08:58:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7B81B6B00A0; Thu, 1 Aug 2024 08:58:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 67FEA6B00A1; Thu, 1 Aug 2024 08:58:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 4A2516B009F for ; Thu, 1 Aug 2024 08:58:01 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id EA55F120D98 for ; Thu, 1 Aug 2024 12:58:00 +0000 (UTC) X-FDA: 82403679120.30.063FEA4 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by imf13.hostedemail.com (Postfix) with ESMTP id 669ED20026 for ; Thu, 1 Aug 2024 12:57:58 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=HJU0E+Fy; spf=pass (imf13.hostedemail.com: domain of broonie@kernel.org designates 145.40.73.55 as permitted sender) smtp.mailfrom=broonie@kernel.org; dmarc=pass (policy=none) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1722517021; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=+YMOH7SGjV5r/wRfXrKGxXbTlZDaSXg1HFoXUP1VHVM=; b=QKgm4OTrFuQKhRb94Ctvz7Ux43gpcTY8q4IJT6Tl/07N6XID+A6n/AG5ijHNAXVUC/gK+G t/edXpCU9GIJ6PFuMJcCwvarPR/vkUmHYY51XEaMKZBdKPc1/8BrY1Euj36lDSVRVw60XC d2WThO8pSbU9Qj41+lwOoXPfBDKZR2Y= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1722517021; a=rsa-sha256; cv=none; b=3r5bKU9y73ihZciCymSLCc+pKpt4V6mOCtPTbCzz9eiKKv/uthbAptQEqfzfaAQCubM7G5 GZURWU9Fyma7Oi1DWsAtUoRI9hqvo2mkivSwQpmuQgKwbDKrBu4nfilIbjDjmXSIIEcv6X dqBcP6CJgP5ffeErKXLkV9AxskMgnu8= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=HJU0E+Fy; spf=pass (imf13.hostedemail.com: domain of broonie@kernel.org designates 145.40.73.55 as permitted sender) smtp.mailfrom=broonie@kernel.org; dmarc=pass (policy=none) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sin.source.kernel.org (Postfix) with ESMTP id F1CE6CE1979; Thu, 1 Aug 2024 12:57:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B369FC32786; Thu, 1 Aug 2024 12:57:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722517074; bh=K9krRCbvH7YvJ22hr22iaSqAjeeG9fR/Lj3PkK3c1RE=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=HJU0E+Fy3pXzTTy/qw3hdomWGawEwi8taNnbgznBdhntqwPPfFVDoRJPQUdE5L5w6 6rp8LTz+DvpHNwUXYEFmCZhI1/AAAmfwnON5k1JuCDjEYnYydCfr5jRJvaxU/Qp/PC y1fJw1NwaD6MAyH9PU/FvQsZydAgHBxJNKA6cT2vQaPdWhqPBq4eMhMEkr6y3JLiue DixNGa6IpRXKgVjPG6SCV0jH+7kHquTUrmVpq1sLnvQCYDM6gn7LuDMldXGV8eL8zi kHHLuwuX/qmA+Y6TnqxubKoMFGRNe6ruICvKpikYiWbFiumhl5HNpY2z++/+3Ww3H0 w2p0qYnetQM1g== From: Mark Brown Date: Thu, 01 Aug 2024 13:06:32 +0100 Subject: [PATCH v10 05/40] arm64/gcs: Document the ABI for Guarded Control Stacks MIME-Version: 1.0 Message-Id: <20240801-arm64-gcs-v10-5-699e2bd2190b@kernel.org> References: <20240801-arm64-gcs-v10-0-699e2bd2190b@kernel.org> In-Reply-To: <20240801-arm64-gcs-v10-0-699e2bd2190b@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 , 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-37811 X-Developer-Signature: v=1; a=openpgp-sha256; l=10734; i=broonie@kernel.org; h=from:subject:message-id; bh=K9krRCbvH7YvJ22hr22iaSqAjeeG9fR/Lj3PkK3c1RE=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBmq4YJIJCwq2KZzv1i43es/92rtkSE5gmxwvGQaEBc 1Qw1DUiJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZquGCQAKCRAk1otyXVSH0OjUB/ 9Z1M0U1ZyhlJl66bkUoB6231eLd2ontVjWDgT0JIyoYVU6XDFvP82UeNOQ5isHQVRYLNpsg6qY6Ytl TbvUDsi+P685/PuynFYnVjeUDUZcqcEDh0iWXa+hvwS04BPOQuDhpZHWYRS2IunfHvJtVxwusBxNb2 4dOwnsOHFR6m+NLKaVXk9oNthVl1XSnS+P4uZBBQGuzBcIR11LUWJ7HUfy/mxp61OExsaB3dEqYDEh MtezfOI6bnUQBrpWVfsumC64SkMXnuh8XPg/QJVlSa2Mydes/ECYQtRETBRAQ7C/LhkW3FxnjOdU2l DUTH7zyQAPb+27WOzdR/PPc1CwDEd7 X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB X-Stat-Signature: byompkiipkjr3d644giqnguj89944k7f X-Rspamd-Queue-Id: 669ED20026 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1722517077-781411 X-HE-Meta: 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 TKu8ohYc cMICkH52kxpmk8ynRcZcBpUJ0qf26QwSW7z+nQcwmon6haYVw402xpWLaRkeBPq9c4TbdvzgHXtsYQhNv65vvhK+WlBTgW+ZAn6sE8UG9h7mX8ZzDdBV075t/3WeNxDGktqNNgzfXJoeeCCBZIXK6PHgNRCks0Xr2afnAvcVtdk/p23TiwPeJfLQE6KT2QJcY3MJVZ5pjGkiSU7PUER80NduZuzWsYDVy7X/J41ZqKr6miwJk5J5MX+FEc/T5BF2WR6ibYMHSKA8INCPBDRbHh6+4t+2DVw4zglWGtpy6E8zjKy1Qa5SxZIrP1CiHjPUUYitJzHJqynlEOTRnodLptsH0VBb1aVsdPXmtFKr1r+I1qydJYYmCVau/AJsZeQqjDoJ1 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Add some documentation of the userspace ABI for Guarded Control Stacks. Reviewed-by: Thiago Jung Bauermann Signed-off-by: Mark Brown --- Documentation/arch/arm64/gcs.rst | 233 +++++++++++++++++++++++++++++++++++++ Documentation/arch/arm64/index.rst | 1 + 2 files changed, 234 insertions(+) diff --git a/Documentation/arch/arm64/gcs.rst b/Documentation/arch/arm64/gcs.rst new file mode 100644 index 000000000000..8b16394b4c29 --- /dev/null +++ b/Documentation/arch/arm64/gcs.rst @@ -0,0 +1,233 @@ +=============================================== +Guarded Control Stack support for AArch64 Linux +=============================================== + +This document outlines briefly the interface provided to userspace by Linux in +order to support use of the ARM Guarded Control Stack (GCS) feature. + +This is an outline of the most important features and issues only and not +intended to be exhaustive. + + + +1. General +----------- + +* GCS is an architecture feature intended to provide greater protection + against return oriented programming (ROP) attacks and to simplify the + implementation of features that need to collect stack traces such as + profiling. + +* When GCS is enabled a separate guarded control stack is maintained by the + PE which is writeable only through specific GCS operations. This + stores the call stack only, when a procedure call instruction is + performed the current PC is pushed onto the GCS and on RET the + address in the LR is verified against that on the top of the GCS. + +* When active the current GCS pointer is stored in the system register + GCSPR_EL0. This is readable by userspace but can only be updated + via specific GCS instructions. + +* The architecture provides instructions for switching between guarded + control stacks with checks to ensure that the new stack is a valid + target for switching. + +* The functionality of GCS is similar to that provided by the x86 Shadow + Stack feature, due to sharing of userspace interfaces the ABI refers to + shadow stacks rather than GCS. + +* Support for GCS is reported to userspace via HWCAP2_GCS in the aux vector + AT_HWCAP2 entry. + +* GCS is enabled per thread. While there is support for disabling GCS + at runtime this should be done with great care. + +* GCS memory access faults are reported as normal memory access faults. + +* GCS specific errors (those reported with EC 0x2d) will be reported as + SIGSEGV with a si_code of SEGV_CPERR (control protection error). + +* GCS is supported only for AArch64. + +* On systems where GCS is supported GCSPR_EL0 is always readable by EL0 + regardless of the GCS configuration for the thread. + +* The architecture supports enabling GCS without verifying that return values + in LR match those in the GCS, the LR will be ignored. This is not supported + by Linux. + +* EL0 GCS entries with bit 63 set are reserved for use, one such use is defined + below for signals and should be ignored when parsing the stack if not + understood. + + +2. Enabling and disabling Guarded Control Stacks +------------------------------------------------- + +* GCS is enabled and disabled for a thread via the PR_SET_SHADOW_STACK_STATUS + prctl(), this takes a single flags argument specifying which GCS features + should be used. + +* When set PR_SHADOW_STACK_ENABLE flag allocates a Guarded Control Stack + and enables GCS for the thread, enabling the functionality controlled by + GCSCRE0_EL1.{nTR, RVCHKEN, PCRSEL}. + +* When set the PR_SHADOW_STACK_PUSH flag enables the functionality controlled + by GCSCRE0_EL1.PUSHMEn, allowing explicit GCS pushes. + +* When set the PR_SHADOW_STACK_WRITE flag enables the functionality controlled + by GCSCRE0_EL1.STREn, allowing explicit stores to the Guarded Control Stack. + +* Any unknown flags will cause PR_SET_SHADOW_STACK_STATUS to return -EINVAL. + +* PR_LOCK_SHADOW_STACK_STATUS is passed a bitmask of features with the same + values as used for PR_SET_SHADOW_STACK_STATUS. Any future changes to the + status of the specified GCS mode bits will be rejected. + +* PR_LOCK_SHADOW_STACK_STATUS allows any bit to be locked, this allows + userspace to prevent changes to any future features. + +* There is no support for a process to remove a lock that has been set for + it. + +* PR_SET_SHADOW_STACK_STATUS and PR_LOCK_SHADOW_STACK_STATUS affect only the + thread that called them, any other running threads will be unaffected. + +* New threads inherit the GCS configuration of the thread that created them. + +* GCS is disabled on exec(). + +* The current GCS configuration for a thread may be read with the + PR_GET_SHADOW_STACK_STATUS prctl(), this returns the same flags that + are passed to PR_SET_SHADOW_STACK_STATUS. + +* If GCS is disabled for a thread after having previously been enabled then + the stack will remain allocated for the lifetime of the thread. At present + any attempt to reenable GCS for the thread will be rejected, this may be + revisited in future. + +* It should be noted that since enabling GCS will result in GCS becoming + active immediately it is not normally possible to return from the function + that invoked the prctl() that enabled GCS. It is expected that the normal + usage will be that GCS is enabled very early in execution of a program. + + + +3. Allocation of Guarded Control Stacks +---------------------------------------- + +* When GCS is enabled for a thread a new Guarded Control Stack will be + allocated for it of size RLIMIT_STACK or 2 gigabytes, whichever is + smaller. + +* When a new thread is created by a thread which has GCS enabled then a + new Guarded Control Stack will be allocated for the new thread with + half the size of the standard stack. + +* When a stack is allocated by enabling GCS or during thread creation then + the top 8 bytes of the stack will be initialised to 0 and GCSPR_EL0 will + be set to point to the address of this 0 value, this can be used to + detect the top of the stack. + +* Additional Guarded Control Stacks can be allocated using the + map_shadow_stack() system call. + +* Stacks allocated using map_shadow_stack() can optionally have an end of + stack marker and cap placed at the top of the stack. If the flag + SHADOW_STACK_SET_TOKEN is specified a cap will be placed on the stack, + if SHADOW_STACK_SET_MARKER is not specified the cap will be the top 8 + bytes of the stack and if it is specified then the cap will be the next + 8 bytes. While specifying just SHADOW_STACK_SET_MARKER by itself is + valid since the marker is all bits 0 it has no observable effect. + +* Stacks allocated using map_shadow_stack() must have a size which is a + multiple of 8 bytes larger than 8 bytes and must be 8 bytes aligned. + +* An address can be specified to map_shadow_stack(), if one is provided then + it must be aligned to a page boundary. + +* When a thread is freed the Guarded Control Stack initially allocated for + that thread will be freed. Note carefully that if the stack has been + switched this may not be the stack currently in use by the thread. + + +4. Signal handling +-------------------- + +* A new signal frame record gcs_context encodes the current GCS mode and + pointer for the interrupted context on signal delivery. This will always + be present on systems that support GCS. + +* The record contains a flag field which reports the current GCS configuration + for the interrupted context as PR_GET_SHADOW_STACK_STATUS would. + +* The signal handler is run with the same GCS configuration as the interrupted + context. + +* When GCS is enabled for the interrupted thread a signal handling specific + GCS cap token will be written to the GCS, this is an architectural GCS cap + token with bit 63 set and the token type (bits 0..11) all clear. The + GCSPR_EL0 reported in the signal frame will point to this cap token. + +* The signal handler will use the same GCS as the interrupted context. + +* When GCS is enabled on signal entry a frame with the address of the signal + return handler will be pushed onto the GCS, allowing return from the signal + handler via RET as normal. This will not be reported in the gcs_context in + the signal frame. + + +5. Signal return +----------------- + +When returning from a signal handler: + +* If there is a gcs_context record in the signal frame then the GCS flags + and GCSPR_EL0 will be restored from that context prior to further + validation. + +* If there is no gcs_context record in the signal frame then the GCS + configuration will be unchanged. + +* If GCS is enabled on return from a signal handler then GCSPR_EL0 must + point to a valid GCS signal cap record, this will be popped from the + GCS prior to signal return. + +* If the GCS configuration is locked when returning from a signal then any + attempt to change the GCS configuration will be treated as an error. This + is true even if GCS was not enabled prior to signal entry. + +* GCS may be disabled via signal return but any attempt to enable GCS via + signal return will be rejected. + + +6. ptrace extensions +--------------------- + +* A new regset NT_ARM_GCS is defined for use with PTRACE_GETREGSET and + PTRACE_SETREGSET. + +* Due to the complexity surrounding allocation and deallocation of stacks and + lack of practical application it is not possible to enable GCS via ptrace. + GCS may be disabled via the ptrace interface. + +* Other GCS modes may be configured via ptrace. + +* Configuration via ptrace ignores locking of GCS mode bits. + + +7. ELF coredump extensions +--------------------------- + +* NT_ARM_GCS notes will be added to each coredump for each thread of the + dumped process. The contents will be equivalent to the data that would + have been read if a PTRACE_GETREGSET of the corresponding type were + executed for each thread when the coredump was generated. + + + +8. /proc extensions +-------------------- + +* Guarded Control Stack pages will include "ss" in their VmFlags in + /proc//smaps. diff --git a/Documentation/arch/arm64/index.rst b/Documentation/arch/arm64/index.rst index 78544de0a8a9..056f6a739d25 100644 --- a/Documentation/arch/arm64/index.rst +++ b/Documentation/arch/arm64/index.rst @@ -15,6 +15,7 @@ ARM64 Architecture cpu-feature-registers cpu-hotplug elf_hwcaps + gcs hugetlbpage kdump legacy_instructions