From patchwork Mon Feb 10 20:26:58 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Deepak Gupta X-Patchwork-Id: 13969354 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CF3C1C0219D for ; Mon, 10 Feb 2025 20:29:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:In-Reply-To:References:Message-Id :MIME-Version:Subject:Date:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=JGBnYRCFj2pq9AMdyqj4UEl4WGlEgnvBxRgQcjbNKgw=; b=hIzmOw3BxBX1b9 VR0ENBM4yew26rnvEH0+xsGTebCa5AOqTo4EYOzwWe+88sse2CRGT0BowvTaS0K92jN4Ky51ubHMy o700c5UJCc4/9Y6TpgGt17/tAvhYNL1/IsFRmxXk01NBakd4rEM1NWir4IkNehA0FpLMlm4d+Myte ZwbZNOR0wZmRz0v6kLOItmBhZ/1iATdmZSdV6+lft80Yu5jBEph22/wL6k06ft3jQDUN0ROn8SXoi 4HwmBwDeaRGuALe+48UvMHeGpXImFPdtBdpSKlPeYaHvJOqZ2f7FNCjfrTBdQAVNC1ZoQA8kTCtNd ivejhT7xuVFO9GfF5m9Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1thaOu-00000001LPq-3EZr; Mon, 10 Feb 2025 20:29:04 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1thaNk-00000001Ksf-3B6i for linux-riscv@bombadil.infradead.org; Mon, 10 Feb 2025 20:27:52 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Cc:To:In-Reply-To:References: Message-Id:Content-Transfer-Encoding:Content-Type:MIME-Version:Subject:Date: From:Sender:Reply-To:Content-ID:Content-Description; bh=vh4CUvpz/fzJO7m3g4Lrx30VWLQNLgBESiJnDVTGIvg=; b=e1GkXwPBPUMa+FF/PEWkcqhPJt SAc+phvKR2e27DptTeDpa1ana+MVRgZ/6RzYBwdtqRRkepEMruERoJJlCGE3LbQDDotoxZfOhcOP/ hBcqF+4QGUzC9mtfMDOeoZYot3mbm/T27A/TjNjh9jAxwUlJSH8OJw4PIBmGTYXCKBVby51kEkC7p taRA3LwNZRUMkl4yoXY0V/nmYNG+HirRslIgq2rlqztFS9YOvrS8YreUl80sh1IjGHR+59kQfFjda yjD2B0y1pfaC0fhkCXr4a1DWOGRf0QPpxQyykxNp5j+FudUsamTrDDyeFvn+ZngRUWfklTFVBPNWs Bba/Fvvw==; Received: from mail-pl1-x632.google.com ([2607:f8b0:4864:20::632]) by desiato.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1thaNe-00000000DvA-438q for linux-riscv@lists.infradead.org; Mon, 10 Feb 2025 20:27:51 +0000 Received: by mail-pl1-x632.google.com with SMTP id d9443c01a7336-21f55fbb72bso56910445ad.2 for ; Mon, 10 Feb 2025 12:27:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1739219264; x=1739824064; darn=lists.infradead.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:from:to:cc:subject:date:message-id :reply-to; bh=vh4CUvpz/fzJO7m3g4Lrx30VWLQNLgBESiJnDVTGIvg=; b=y1E1+wVbW6ve9YQ2fwXzzizK7wcM+XJmD1Usst03IMRcIihDfrskpsrmYmiJsqN1h1 r/66OdHYeqmvHuovhMIm6opRs0HRUjD3A/IN7F2sxc0Ln1woB9GFkD3NQ1s+NXRqOJEq VlWZZdrNuC+ObRRmrbqL5bDyTrE1Mct5Rg3K0M8/A7gkgY5K2uAoYAA7ifPwteS+deug XTXNeyhZpHMTTLOXgXEjVCbIRQoo+0csYMZAUpx0rdsZtx4uwMghz6D1go+MzBMOavHL YsuoacsmbiH7JDWcn39cgzTxyfzvMlkMkLD/o0sFlMViUpf8LZtexLxeQf4belgZvXym Pc/w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739219264; x=1739824064; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=vh4CUvpz/fzJO7m3g4Lrx30VWLQNLgBESiJnDVTGIvg=; b=VYyqsCx8WJrBdxaQ18FSuoVf0UC3CUhMVmUlHdkgxHTt7ae9ZoBX92E9x451BHWTxd 5u73RgZhokqtmDyyQsbjbGoopvGMHT6InenEhYslbiokA0lSEkEzQfXe8OPHra7Oubks TUsEHNG8DT4nQs9V2EpHumU3HX2iu/WBNcO7AGkESdMDXPTVouv1uI79Aw1eWeu+ssPY jctqOpmlbycqetoTsY5Ecg4QTURrrdVPA4CWyieaXgQPxbNzzAAscEFJ6LhSFUUkwHNn yCEeP3qsGlUvfwCygw4jLe7+G8YcD5O9lHvUzJ1lGB/WbavV0H4GmV3vYe9FB+8HtypD M2VQ== X-Forwarded-Encrypted: i=1; AJvYcCUtGdOJs0FfB34voNFS9upvqmCqCRl+QSNRG5aAkenNLcNiV92aBFJi08EcqxuyDkPR5shcf+cmBMA+kg==@lists.infradead.org X-Gm-Message-State: AOJu0Yytd0/XJcYJ9gUTrY20AbCPmyabMU1PA6MpjqTvvOKc8tJL3o/u roJdXCAcFveyg5U8fwsIbzzjJGb03bQwd/JYnzBlQLphqI2aXEtqtSd+HjwsrcA= X-Gm-Gg: ASbGnctd429NqSA4VPnwb1RdLFbVDi0zPwUkD9VP4Wk/7lUG0sgUQE3KWZaUpGWqBS9 Hbn5BMoqRicPsnYC/d0eQt436oFTr/RuioAKyCZd4DHawGfYSz6SjywFo5TQ5136bbTbjO7kBHP uMRlp1GNlhe9nHSzFmnTzYcrPy8yetnMiuaLE5ofK8sqeAnIXTmp0Ro4RNA1hIvX2TMGUAf9v/s 0UH78GrveU3eoCWbDcBkPOE9IJ8G4kUsvMXJlXXAQzlfIzeqyD52WaNpu3YRK0pHTalxv3f5F9l QK2ZxExzZANnIKs2GZrZsY+AqQ== X-Google-Smtp-Source: AGHT+IHONYQapq26xKI/Nlqt2sawgQ5ST7q18FCOtyS0Axv9TidoEnrL+FFU0G/ytCjykvg19tyLYQ== X-Received: by 2002:a17:902:d4cc:b0:21f:6a36:7bf3 with SMTP id d9443c01a7336-21f6a369009mr211502955ad.12.1739219264447; Mon, 10 Feb 2025 12:27:44 -0800 (PST) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-21f3687c187sm83711555ad.168.2025.02.10.12.27.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Feb 2025 12:27:44 -0800 (PST) From: Deepak Gupta Date: Mon, 10 Feb 2025 12:26:58 -0800 Subject: [PATCH v10 25/27] riscv: Documentation for landing pad / indirect branch tracking MIME-Version: 1.0 Message-Id: <20250210-v5_user_cfi_series-v10-25-163dcfa31c60@rivosinc.com> References: <20250210-v5_user_cfi_series-v10-0-163dcfa31c60@rivosinc.com> In-Reply-To: <20250210-v5_user_cfi_series-v10-0-163dcfa31c60@rivosinc.com> To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , Paul Walmsley , Palmer Dabbelt , Albert Ou , Conor Dooley , Rob Herring , Krzysztof Kozlowski , Arnd Bergmann , Christian Brauner , Peter Zijlstra , Oleg Nesterov , Eric Biederman , Kees Cook , Jonathan Corbet , Shuah Khan , Jann Horn , Conor Dooley Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, alistair.francis@wdc.com, richard.henderson@linaro.org, jim.shu@sifive.com, andybnac@gmail.com, kito.cheng@sifive.com, charlie@rivosinc.com, atishp@rivosinc.com, evan@rivosinc.com, cleger@rivosinc.com, alexghiti@rivosinc.com, samitolvanen@google.com, broonie@kernel.org, rick.p.edgecombe@intel.com, Deepak Gupta X-Mailer: b4 0.14.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250210_202749_388254_A948C83E X-CRM114-Status: GOOD ( 19.41 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org 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/index.rst | 1 + Documentation/arch/riscv/zicfilp.rst | 115 +++++++++++++++++++++++++++++++++++ 2 files changed, 116 insertions(+) diff --git a/Documentation/arch/riscv/index.rst b/Documentation/arch/riscv/index.rst index eecf347ce849..be7237b69682 100644 --- a/Documentation/arch/riscv/index.rst +++ b/Documentation/arch/riscv/index.rst @@ -14,6 +14,7 @@ RISC-V architecture uabi vector cmodx + zicfilp features diff --git a/Documentation/arch/riscv/zicfilp.rst b/Documentation/arch/riscv/zicfilp.rst new file mode 100644 index 000000000000..a188d78fcde6 --- /dev/null +++ b/Documentation/arch/riscv/zicfilp.rst @@ -0,0 +1,115 @@ +.. 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 :c:macro:`GNU_PROPERTY_RISCV_FEATURE_1_FCFI` for property +:c:macro:`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 +-------------------- + +:c:macro:`PR_SET_INDIR_BR_LP_STATUS` / :c:macro:`PR_GET_INDIR_BR_LP_STATUS` / +:c:macro:`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. + +* prctl(PR_SET_INDIR_BR_LP_STATUS, unsigned long arg) + +If arg1 is :c:macro:`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 :c:macro:`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. +:c:macro:`PR_INDIR_BR_LP_ENABLE` being clear) + +* prctl(PR_GET_INDIR_BR_LP_STATUS, unsigned long arg) + +Returns current status of indirect branch tracking. If enabled it'll return +:c:macro:`PR_INDIR_BR_LP_ENABLE` + +* prctl(PR_LOCK_INDIR_BR_LP_STATUS, unsigned long arg) + +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 :c:macro:`SIGSEV`` with code = +:c:macro:`SEGV_CPERR` and follow normal course of signal delivery.