From patchwork Thu Sep 12 23:16:47 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Deepak Gupta X-Patchwork-Id: 13802878 Received: from mail-pl1-f170.google.com (mail-pl1-f170.google.com [209.85.214.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9BCB71D54DA for ; Thu, 12 Sep 2024 23:19:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726183151; cv=none; b=Ru+QujJl8ne8ED1MAQs5qzX3k1uSXyzH1FyZnhkbksT4C5qGH9ReuLH8gacxQUllFay1ajevgDv2jLKPOZZH65qF+B6xxNzNW+5LAc1wbncpHY96K6s8QV+m9io2v2XBWK+3O6fmYdWnApwiT/fgNgz64fZurL1OEtmxALLawM4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726183151; c=relaxed/simple; bh=P43D1caEJmaZtlsnwossu8IhPK41eS+mTAY7SmhqKsI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oYwW9hss1Sj5oNe8AeNehYtwdt1PGhiiaYbJzn7X9i9wZV0i7cZWW9K0nWQ9DIKrNlfm9TIqxCGMu+ZtVHqQ3DovsWohRshVgAexS+HCI44nLJAnTMUFYQJKqjPoqpJeUjXjwqCQ7gQEPSH5F6EVXInfYLk1J2Mw+Q/Twqivikc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=rivosinc.com; spf=pass smtp.mailfrom=rivosinc.com; dkim=pass (2048-bit key) header.d=rivosinc-com.20230601.gappssmtp.com header.i=@rivosinc-com.20230601.gappssmtp.com header.b=020ITdSn; arc=none smtp.client-ip=209.85.214.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=rivosinc.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=rivosinc.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=rivosinc-com.20230601.gappssmtp.com header.i=@rivosinc-com.20230601.gappssmtp.com header.b="020ITdSn" Received: by mail-pl1-f170.google.com with SMTP id d9443c01a7336-20536dcc6e9so2256585ad.2 for ; Thu, 12 Sep 2024 16:19:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1726183149; x=1726787949; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=Iyonew7njYYUDgOFlccFcLDkYmWknDQSdFdIbsgjEzE=; b=020ITdSnaTdVEdf9cwfgw/dDNEHKyUXBSbiE9gGY7IJr7XG9TY1Sc3hjeWcgFMrfmS 6n71gVtQlpuajn0Q1dufD61WoQ0TxEvvLGtL0fPFvb/Xfva0JQgbM8MbCwUI/wXNZYLO vnNZNgsyh4lu1sPN0pNr5AJIfTIpwOXpgVbnSyJRG1nW+PCf5E9bayv4EjXW3Z2mAXhq J795VQIWAoydg2jY9hxNydGJd7NM/3LXeaBkxrDAbS0gUGyNw7EKt9TuvhkL4JH6+PAl K2B1Xy6M/xnOccZ1I4IzkFy6F/tGg565VfBxgItH36b0JOcmNJttpfnwEMhyC/x5vVib FgYg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1726183149; x=1726787949; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=Iyonew7njYYUDgOFlccFcLDkYmWknDQSdFdIbsgjEzE=; b=Ghlw69dT+5qMbQQESUu81YdnJgQlYLNzJ9bzXLe660V6AP+8ajAw4sPYjwiq3BpQIM 3Ws/NY8zrnctevVREjwiPdA+Csf48qX2ywFaPIPQY87DglqpffvXGt1xB0L4c7Ypq8Fh +y8nqNxcSP8ydolQN2EkyH+e84Hpv9ZSrblNfpt7YjgT0a6z7qeHC0nUIrCslQAQH29G IoI9BBthpNYkUTRwru6I8SjsiyvJxT6lOsEs6PLR6JKK+RQpNtEb7kUDcPVdbeIuC6wR hxhP9ZL+CrqUV9FYolkpBEHcJSyZI2011P/5+RiW9N+ERWO2VNN3psiPlrZ+AhCiBJ6u rt/Q== X-Forwarded-Encrypted: i=1; AJvYcCUOzLLdNtgeApfiFr/vuLxPKb73kMURZEJpS1h4R9V96TXcxP81XeptaHJ+bhX1sXpV2sb4VBOKYEs6RXptR0g=@vger.kernel.org X-Gm-Message-State: AOJu0Yz2X2yrgt9livUWt+/SgV6ngFTASrKWtQqBRwITJrQtGFspMcv0 2olmofa95DA5BFXBumEHzITX3BKJqzFgcoT4wIEwqUs6LbtnKFGGMNLx/RgVrpY= X-Google-Smtp-Source: AGHT+IFQFXeegIq20jMre9WaWvSrfHhLDrwK4rARP/3T0r/5M87gFpvdLVA9mkxvLCR99S6cpVQrqw== X-Received: by 2002:a17:90a:4b87:b0:2d8:f0b4:9acb with SMTP id 98e67ed59e1d1-2dbb9f08179mr1017556a91.34.1726183148685; Thu, 12 Sep 2024 16:19:08 -0700 (PDT) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2db6c1ac69asm3157591a91.0.2024.09.12.16.19.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Sep 2024 16:19:08 -0700 (PDT) From: Deepak Gupta To: paul.walmsley@sifive.com, palmer@sifive.com, conor@kernel.org, linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: corbet@lwn.net, palmer@dabbelt.com, aou@eecs.berkeley.edu, robh@kernel.org, krzk+dt@kernel.org, oleg@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, akpm@linux-foundation.org, arnd@arndb.de, ebiederm@xmission.com, kees@kernel.org, Liam.Howlett@oracle.com, vbabka@suse.cz, lorenzo.stoakes@oracle.com, shuah@kernel.org, brauner@kernel.org, samuel.holland@sifive.com, debug@rivosinc.com, andy.chiu@sifive.com, jerry.shih@sifive.com, greentime.hu@sifive.com, charlie@rivosinc.com, evan@rivosinc.com, cleger@rivosinc.com, xiao.w.wang@intel.com, ajones@ventanamicro.com, anup@brainfault.org, mchitale@ventanamicro.com, atishp@rivosinc.com, sameo@rivosinc.com, bjorn@rivosinc.com, alexghiti@rivosinc.com, david@redhat.com, libang.li@antgroup.com, jszhang@kernel.org, leobras@redhat.com, guoren@kernel.org, samitolvanen@google.com, songshuaishuai@tinylab.org, costa.shul@redhat.com, bhe@redhat.com, zong.li@sifive.com, puranjay@kernel.org, namcaov@gmail.com, antonb@tenstorrent.com, sorear@fastmail.com, quic_bjorande@quicinc.com, ancientmodern4@gmail.com, ben.dooks@codethink.co.uk, quic_zhonhan@quicinc.com, cuiyunhui@bytedance.com, yang.lee@linux.alibaba.com, ke.zhao@shingroup.cn, sunilvl@ventanamicro.com, tanzhasanwork@gmail.com, schwab@suse.de, dawei.li@shingroup.cn, rppt@kernel.org, willy@infradead.org, usama.anjum@collabora.com, osalvador@suse.de, ryan.roberts@arm.com, andrii@kernel.org, alx@kernel.org, catalin.marinas@arm.com, broonie@kernel.org, revest@chromium.org, bgray@linux.ibm.com, deller@gmx.de, zev@bewilderbeest.net Subject: [PATCH v4 28/30] riscv: Documentation for landing pad / indirect branch tracking Date: Thu, 12 Sep 2024 16:16:47 -0700 Message-ID: <20240912231650.3740732-29-debug@rivosinc.com> X-Mailer: git-send-email 2.45.0 In-Reply-To: <20240912231650.3740732-1-debug@rivosinc.com> References: <20240912231650.3740732-1-debug@rivosinc.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Adding documentation on landing pad aka indirect branch tracking on riscv and kernel interfaces exposed so that user tasks can enable it. Signed-off-by: Deepak Gupta --- Documentation/arch/riscv/zicfilp.rst | 104 +++++++++++++++++++++++++++ 1 file changed, 104 insertions(+) create mode 100644 Documentation/arch/riscv/zicfilp.rst diff --git a/Documentation/arch/riscv/zicfilp.rst b/Documentation/arch/riscv/zicfilp.rst new file mode 100644 index 000000000000..23013ee711ac --- /dev/null +++ b/Documentation/arch/riscv/zicfilp.rst @@ -0,0 +1,104 @@ +.. SPDX-License-Identifier: GPL-2.0 + +:Author: Deepak Gupta +:Date: 12 January 2024 + +==================================================== +Tracking indirect control transfers on RISC-V Linux +==================================================== + +This document briefly describes the interface provided to userspace by Linux +to enable indirect branch tracking for user mode applications on RISV-V + +1. Feature Overview +-------------------- + +Memory corruption issues usually result in to crashes, however when in hands of +an adversary and if used creatively can result into variety security issues. + +One of those security issues can be code re-use attacks on program where adversary +can use corrupt function pointers and chain them together to perform jump oriented +programming (JOP) or call oriented programming (COP) and thus compromising control +flow integrity (CFI) of the program. + +Function pointers live in read-write memory and thus are susceptible to corruption +and allows an adversary to reach any program counter (PC) in address space. On +RISC-V zicfilp extension enforces a restriction on such indirect control transfers + + - indirect control transfers must land on a landing pad instruction `lpad`. + There are two exception to this rule + - rs1 = x1 or rs1 = x5, i.e. a return from a function and returns are + protected using shadow stack (see zicfiss.rst) + + - rs1 = x7. On RISC-V compiler usually does below to reach function + which is beyond the offset possible J-type instruction. + + "auipc x7, " + "jalr (x7)" + + Such form of indirect control transfer are still immutable and don't rely + on memory and thus rs1=x7 is exempted from tracking and considered software + guarded jumps. + +`lpad` instruction is pseudo of `auipc rd, ` with `rd=x0`` and is a HINT +nop. `lpad` instruction must be aligned on 4 byte boundary and compares 20 bit +immediate withx7. If `imm_20bit` == 0, CPU don't perform any comparision with x7. If +`imm_20bit` != 0, then `imm_20bit` must match x7 else CPU will raise +`software check exception` (cause=18)with `*tval = 2`. + +Compiler can generate a hash over function signatures and setup them (truncated +to 20bit) in x7 at callsites and function prologues can have `lpad` with same +function hash. This further reduces number of program counters a call site can +reach. + +2. ELF and psABI +----------------- + +Toolchain sets up `GNU_PROPERTY_RISCV_FEATURE_1_FCFI` for property +`GNU_PROPERTY_RISCV_FEATURE_1_AND` in notes section of the object file. + +3. Linux enabling +------------------ + +User space programs can have multiple shared objects loaded in its address space +and it's a difficult task to make sure all the dependencies have been compiled +with support of indirect branch. Thus it's left to dynamic loader to enable +indirect branch tracking for the program. + +4. prctl() enabling +-------------------- + +`PR_SET_INDIR_BR_LP_STATUS` / `PR_GET_INDIR_BR_LP_STATUS` / +`PR_LOCK_INDIR_BR_LP_STATUS` are three prctls added to manage indirect branch +tracking. prctls are arch agnostic and returns -EINVAL on other arches. + +`PR_SET_INDIR_BR_LP_STATUS`: If arg1 `PR_INDIR_BR_LP_ENABLE` and if CPU supports +`zicfilp` then kernel will enabled indirect branch tracking for the task. +Dynamic loader can issue this `prctl` once it has determined that all the objects +loaded in address space support indirect branch tracking. Additionally if there is +a `dlopen` to an object which wasn't compiled with `zicfilp`, dynamic loader can +issue this prctl with arg1 set to 0 (i.e. `PR_INDIR_BR_LP_ENABLE` being clear) + +`PR_GET_INDIR_BR_LP_STATUS`: Returns current status of indirect branch tracking. +If enabled it'll return `PR_INDIR_BR_LP_ENABLE` + +`PR_LOCK_INDIR_BR_LP_STATUS`: Locks current status of indirect branch tracking on +the task. User space may want to run with strict security posture and wouldn't want +loading of objects without `zicfilp` support in it and thus would want to disallow +disabling of indirect branch tracking. In that case user space can use this prctl +to lock current settings. + +5. violations related to indirect branch tracking +-------------------------------------------------- + +Pertaining to indirect branch tracking, CPU raises software check exception in +following conditions + - missing `lpad` after indirect call / jmp + - `lpad` not on 4 byte boundary + - `imm_20bit` embedded in `lpad` instruction doesn't match with `x7` + +In all 3 cases, `*tval = 2` is captured and software check exception is raised +(cause=18) + +Linux kernel will treat this as `SIGSEV`` with code = `SEGV_CPERR` and follow +normal course of signal delivery.