From patchwork Mon Mar 10 14:52:47 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Deepak Gupta X-Patchwork-Id: 14010215 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 8B0CBC282DE for ; Mon, 10 Mar 2025 14:53:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 12915280021; Mon, 10 Mar 2025 10:53:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0B81A280017; Mon, 10 Mar 2025 10:53:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DF0F9280021; Mon, 10 Mar 2025 10:53:37 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id BDB95280017 for ; Mon, 10 Mar 2025 10:53:37 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 3DA8D8119B for ; Mon, 10 Mar 2025 14:53:38 +0000 (UTC) X-FDA: 83205935316.04.62ADA99 Received: from mail-pl1-f178.google.com (mail-pl1-f178.google.com [209.85.214.178]) by imf20.hostedemail.com (Postfix) with ESMTP id 511581C001A for ; Mon, 10 Mar 2025 14:53:36 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=rivosinc-com.20230601.gappssmtp.com header.s=20230601 header.b=XHpPAoly; spf=pass (imf20.hostedemail.com: domain of debug@rivosinc.com designates 209.85.214.178 as permitted sender) smtp.mailfrom=debug@rivosinc.com; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1741618416; 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=vh4CUvpz/fzJO7m3g4Lrx30VWLQNLgBESiJnDVTGIvg=; b=vj0fi0P5IEsloiyyxaF5EqLksVtMsyy3/Vta+57XmM2rNl/wfBmjRKI7Obh4LP+pJLWz3n 01kAdY2npA64dqgiS9MYwEznJwYYtySpvnxXdmwjE2PF+3nOOhnkizv4euQvT36mnKKu1z bRrc82V1QS7hk2TIQBuJqHk0fC7ExyI= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=rivosinc-com.20230601.gappssmtp.com header.s=20230601 header.b=XHpPAoly; spf=pass (imf20.hostedemail.com: domain of debug@rivosinc.com designates 209.85.214.178 as permitted sender) smtp.mailfrom=debug@rivosinc.com; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1741618416; a=rsa-sha256; cv=none; b=n6CKNgbFUd76pMv3s67hV1+IRrx8xEX4eTWlsJJJRPfwMjm0tcVw8bfON32QLI3sucrYxg 9A16gqCqUUiQGQ/+1HiIm+mWMlRv4Roh26x1SbUtAk9gFF0Z8eLx6HS489fstL1pvVCQK+ GOZFSUdp9rTGd0v/UfaSPPa93RfFmOk= Received: by mail-pl1-f178.google.com with SMTP id d9443c01a7336-22548a28d0cso11750415ad.3 for ; Mon, 10 Mar 2025 07:53:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1741618415; x=1742223215; darn=kvack.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=XHpPAolysBMj+b4aefVVntOMMH3TwP1IE9OTqWWe7F9oz3fsL2AB1Y1K9bVBzXEcvC QOGmgntziO/iiluhKSLDX0yRiJZusR/mBnQYqWkm3w/owvhnj9mogaenBooGw8iQ2t3G IcPtoeXFrj8EY4gPDSaXb6yONNVcFsj8Xa6rYTNHrNYYJQba7g5IcQUE1qs7cDIj9f1I yk8yATh0SMSGILP3ZOnWkw14uUYo5PLC7loeGvSzUa4d/pVxhtxiOokNZSUlNM1ZFNg8 T/L8Bn6H6d+VB34QFH+0WTbHETYq62BbXoaBfDP2XVgid4Ak49Uq6fs9Hf5G5gcpbkvO iCPw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741618415; x=1742223215; 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=JA22xFYl2z7D/q7SgqMU7yAdtMIMXaaBaSxjJ8uxwLT84AvRjig0dkWliJW2h4ocG6 VHMuBX0SwebpEbeIL5Tu+35rcZy/5Biuwi+RsKyVpeY7L4hsu+qRBp3a9TCS/ARDuvir Ms1CMoglc38U69J3Q7FCEXocF4DDWnTu6KVkY+bmNa6pcZb9DkTIvdzsk5rWoq/gm6PQ 29PlRPpLKsnDPN+qRvo/Gg2kDQepFfYzl13XRqPqk+3BeemO56rzCn/wzgYiPLsB6Ecn d18DYYGvtBzWdqjU4zP9S0Ov/AILVHR+0U4dC8qqLn4BxDpouL5pJoFiH8Gr7PbfiILU KmKg== X-Forwarded-Encrypted: i=1; AJvYcCWro6D3s4PoGhWvLtUZ7m6MZN5c0c352rF17wWM9/5t68oCNThEND0ilLeGSEksDr9rdIjhklDOQg==@kvack.org X-Gm-Message-State: AOJu0YzlWfwNON0fUL+30JZdjAM8jZfMbOTFhcOk1IkocH956KP/zsUq YmBvPZkeOG8VZBdt3XwrVQMou9Mvyd2m/Hzs6l5UW/cj7HK4+rziAF/wrfVqrNk= X-Gm-Gg: ASbGncvAEBSu9BJTxnqKkkFR6mqgg1/ycb+aObJsjdPu09fKBoz5wYw7HUwX+DSq64Y uktuG9Y/4s2IYJs5ID4qTb9JNVxEbvS7YTbKJYzDsRfNddJi7WRVHIN6xNCGPLr3Ir5XC2gSd3d iNIbv3dxG7fBLjnTPnOrVe9Gg9iRtIapfQv7GukGfRIcR2TXtyXI+DMCxhOSksJYKi7n/8IQaEV AEx6tgQwOiptKR+ubtIWc+JIkKxLl0Gi+n87BPzVh7KgdBNlrtf+Bqbg2zJAO7OGQS8xscAS7X5 GHEzGpY1P5mlFDh1f7NoX3JkQUbXCW2nbLLVdxSMq5x5wpIdSZIhEqw= X-Google-Smtp-Source: AGHT+IHk6fUGtyziYf/rEaJOxRl/jM9mUkmR597ae136siDXwL+YfMuIUi90ii9WUsyzBw7fk0+kRg== X-Received: by 2002:a05:6a21:158c:b0:1f5:837b:186a with SMTP id adf61e73a8af0-1f5837b19c4mr4882849637.6.1741618413790; Mon, 10 Mar 2025 07:53:33 -0700 (PDT) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-736d11d4600sm2890275b3a.116.2025.03.10.07.53.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Mar 2025 07:53:33 -0700 (PDT) From: Deepak Gupta Date: Mon, 10 Mar 2025 07:52:47 -0700 Subject: [PATCH v11 25/27] riscv: Documentation for landing pad / indirect branch tracking MIME-Version: 1.0 Message-Id: <20250310-v5_user_cfi_series-v11-25-86b36cbfb910@rivosinc.com> References: <20250310-v5_user_cfi_series-v11-0-86b36cbfb910@rivosinc.com> In-Reply-To: <20250310-v5_user_cfi_series-v11-0-86b36cbfb910@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-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 511581C001A X-Stat-Signature: kcn38s165niqnf3z6zkot6sbpdfag15k X-Rspam-User: X-HE-Tag: 1741618416-367165 X-HE-Meta: U2FsdGVkX19BVL+sdoMOIoVyB01Wy7zGCGfR/MIEjDdyjYq3ycWjRZKfAOf1YwzldZgLd4VApww8/ePB3Sti/hHokN14TI8+2UJ0qdKgxf8JevqPPBg09ZE+FQLYjCBm6dd//W2XrejodPUF2XW6FbaLyJ3vfkJoA0HI5t4u+OdfT2Y1WRNdr4FgVBkkkG2sx+cGWrgd2R2l937G+mIRJYNmuXAZf87uAh3Hq4BFvZFc484XBROuxsQK0F3wl6X1pmb/s2zR0IiNp7t3GUUtFaS5vRpK87ikzTSExdHckcLInS5fsUozIF3pHUsE81DZhsZxOFE4RUrFOAeQpV1lu1ZQFW4uDSsR7TmxPZHA1k6DIpzUYqo19Fw11Uy772oRpHe2xBntfH0WGG/sIdgC+jrawF/MSq8EUBVkbv8z17pKiMlxHlzsmhI156uCdGMWGm6EJEU+Wr951MRL253tfCSF3MT83QkgWvA0uEwa+f2QEV3PoDof+kGnLOAfmaKDOMUBu1atxOYYlOf/8pBWC8AVlwQEWyfQP3GdlRrDLQ0OsuOzch8hfWq3iRc9mnLpXqKlQhypfQ3+pUzWhjtyzRtGaEIm5/SsBVP67KCQFOZPmCS4fq6jJhkrTXCQWobFsyM5hPvZ2Hs4WLkttbMeE4I2yl7Kstuk5KDKRkKLvjNLq0F0lN9ltERG2/mXSpVTA4ZAbsKEHV4P+BiT11dnGkdps2VU/WGG61butJ5ldNRyMgnogtMoUV2aM2gaoyoePg30JQTADZ5q/hkxV4lv0vDQ7d6o9GSVnumIO2qCTB611LCxY2r9PrJ99PyoT7NPKpWoEzMONzPJ8HGOMF3AohwT8s+Y4QC0MiIUszvDEmBefXx0bBrtBHg/n0vOJ5oDOijrw8TF84/28BZaEc+XLQ7VSgMwEFgPd8cbJn2kHA+6tEeD8EXIqDXqt5ajW33A9kWsHLKVTT1dpVioPOB G4kAFyYc 47GfYubD9mbJ9QNpasiPCjB5rDSMMa/WKkxTiB9Vq8kWKK+RN6FTXT5svgtnQfViw31GeCsM9aCBa1uJi8jFi+KeeJRe4f7ty1KR92NszBAijHb7E0KutJxs+REc8vSbQCsfP/c68ZHzXK4ehfLdyfRJmK8Y7T9GOigY1m9OV+6xwHySr9l3TeC7tAfQMgBBAqG7gKxJRikrkFzWVfp5jYSeKJBVvAMRwwPGwGNi3K5rIRAcaJwwzXytSRUZsv/bvOV0PZKSuDYJrKlhCmaSZyMveM/ePVex+rxOsId3Y4rKkwKWO0jBoQwj9kXQeLTqrXXAD9HbtiXx7ELRkjypdYdj0nmS+6WXvnfKPhnWbxxHvhr4Y5z0/lyQGxgK8WshsguNV3f/cXX6lsppvMDslrTqpAjK6RDmNKAjt2z1WuDpyj/iT5uUB6ks4YKfH40uxorj8xfiwN00IVi9B0FGjJFBTYw== 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: 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.