From nobody Wed Feb 11 02:55:01 2026 Received: from mail-ua1-f54.google.com (mail-ua1-f54.google.com [209.85.222.54]) (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 84BE121D5B4 for ; Thu, 24 Apr 2025 07:21:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.222.54 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745479278; cv=none; b=FZk7HfY8fBwZyfdCT8gfdOC+F327qlcCOlALufsKl/XMCWQrZVDssfdzC/HVyI62Vx4T2cY262tY0ALogyHvgJEgSigblkPsp+iEMOX/IIbFuAu25O9ZQlB/uKDRpim66OY8DaNm1JF6AbFYrBNNv3zVETrlZZZDCihLhL3EHxc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745479278; c=relaxed/simple; bh=MWHORhhDrzBD5xYKXHmYuqbsYg8MAv5FLe7duVKblSA=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=HGjXKemjrAA36nPoYPnFYrcbclCIp+HnX7D/+E/U2Bjq39xGvQSNh/nV3KtLm3F753f0Km4gO52s5f0emr0Yw0a/eluHMr4SqrP/LXIylqVUZ5CzmNGrxi7VhmvtcpNGTLBbXbc45joTitHPodT14Yby2hnI1NoYMp/EHU0aq/8= 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=ET4QH+GV; arc=none smtp.client-ip=209.85.222.54 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="ET4QH+GV" Received: by mail-ua1-f54.google.com with SMTP id a1e0cc1a2514c-86d587dbc15so757225241.1 for ; Thu, 24 Apr 2025 00:21:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1745479275; x=1746084075; darn=vger.kernel.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=uTOlWSgIfNg/m3Oqt+BmGM6XFRmcXruZeuBu1MNVaGQ=; b=ET4QH+GVNCRFN1JbOvl8nGb/7xbcxSsLSkulwHdLlIBT4Cx9/1TAk48TJgrjhNvklh 0eCB65DfS5gMsmlVIiI8n1ZkwidvpNAHDRFIPoFYTgvUassC99DyElnSdVc4dMGxPGA1 MFkdna2viYLu3oWVwfQ4MrQFviQIJTCrwxcFyYTzEvkSzwUquOZcU7yPIROKhNCn5UFT zkWLMPJucgGpVkqGivJ8vfgGY3QbauYIC2wp7aopLNeaQ8vUdk3BUXmVDxU4+hdKmZRi dSsWa6dw+N5hUEzucZajtyEugU6J0YS62IbspTv6lSHJV5RXWlhImY0XI6vgYqM8M+6B 5soQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1745479275; x=1746084075; 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=uTOlWSgIfNg/m3Oqt+BmGM6XFRmcXruZeuBu1MNVaGQ=; b=DQCAK4bIjmDAvbJHBuieHGPDwVz0KxTlb1xklVleq9HUNCmTElSGJ/2FaFU8A9NRbq PlI6OddFBF3ut0io5KceJBGYcntc6U/bg8wABTR0v7V1s4Xf7swcKGyhgtOysaQjWezw Sbf8kwR+WFIQtus5nCuDUSxFrs5WOmbp4XhmlvKeg5PxkuXoF0R6Av5RhURq/7Sn9PGj 6GAumFHshNnytbyZ6x38loNkFVz+xMw8SAfnYIklfRvGg3ljAhkqWm1Jx9VTXMNEJYlD U86EA4Xg3OQV7lSeDu9dDAXXKoQM4tH2N3+Q+yGX0Cd89p4ZhElm079haBDuWVaYH1nQ g3cg== X-Gm-Message-State: AOJu0YybTJnRE4F+VDhQLsVW0DdSjqNmZ8fx2XGLeTZcBa2GO349K7WG 49g6jleiIpkKcE8P2wkl9cYGqtZjzCXIBguyDQ94I3EVCZMrA9YUgsg/He4sPE8= X-Gm-Gg: ASbGncupyQbxSL6QwEt0vuSENOo4eP5al0efQ3lD1sRGrErodrxBoN3LIkJ2YdmM2rE zuz64zJ184N3rcooUzVPyMCMA1ARz0CDIYvNJrcBudveMANF9aXqwAF7/6pmhf7bEHPY3ZfKK8C qD6QPyHkhbR9kjhn5AC0rgvdkwu7bAQg4FIXLvat2d14gZg7Z480fCAVn3kSsHfTNb/M2w9o738 WsLLwQr4JJ+/pvAvjgq1UpYH59xWaqbSEILXuPqru0jNH1ZBfYA+W+HAtoeTK5ZWGNFZDwhI4e1 nTFDeIHOdcK6i4i2Kui9ozd2G3U5By7J8Au3UIOqm69Num/DLWcwRvi0GsqtAQ== X-Google-Smtp-Source: AGHT+IG6rfYKWcrpqCiMIv7u+v5lHTdXwUfRT7tn0rH3sRxk3D1hWLROMKGb0/WJjtbUj6Z//dN74Q== X-Received: by 2002:a17:903:2290:b0:215:ba2b:cd55 with SMTP id d9443c01a7336-22db47ad1c7mr19626865ad.2.1745479264519; Thu, 24 Apr 2025 00:21:04 -0700 (PDT) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22db52163d6sm6240765ad.214.2025.04.24.00.21.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Apr 2025 00:21:04 -0700 (PDT) From: Deepak Gupta Date: Thu, 24 Apr 2025 00:20:28 -0700 Subject: [PATCH v13 13/28] prctl: arch-agnostic prctl for indirect branch tracking 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: <20250424-v5_user_cfi_series-v13-13-971437de586a@rivosinc.com> References: <20250424-v5_user_cfi_series-v13-0-971437de586a@rivosinc.com> In-Reply-To: <20250424-v5_user_cfi_series-v13-0-971437de586a@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 , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross 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, rust-for-linux@vger.kernel.org, Zong Li , Deepak Gupta X-Mailer: b4 0.13.0 Three architectures (x86, aarch64, riscv) have support for indirect branch tracking feature in a very similar fashion. On a very high level, indirect branch tracking is a CPU feature where CPU tracks branches which uses memory operand to perform control transfer in program. As part of this tracking on indirect branches, CPU goes in a state where it expects a landing pad instr on target and if not found then CPU raises some fault (architecture dependent) x86 landing pad instr - `ENDBRANCH` arch64 landing pad instr - `BTI` riscv landing instr - `lpad` Given that three major arches have support for indirect branch tracking, This patch makes `prctl` for indirect branch tracking arch agnostic. To allow userspace to enable this feature for itself, following prtcls are defined: - PR_GET_INDIR_BR_LP_STATUS: Gets current configured status for indirect branch tracking. - PR_SET_INDIR_BR_LP_STATUS: Sets a configuration for indirect branch tracking. Following status options are allowed - PR_INDIR_BR_LP_ENABLE: Enables indirect branch tracking on user thread. - PR_INDIR_BR_LP_DISABLE; Disables indirect branch tracking on user thread. - PR_LOCK_INDIR_BR_LP_STATUS: Locks configured status for indirect branch tracking for user thread. Reviewed-by: Mark Brown Reviewed-by: Zong Li Signed-off-by: Deepak Gupta --- include/linux/cpu.h | 4 ++++ include/uapi/linux/prctl.h | 27 +++++++++++++++++++++++++++ kernel/sys.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 61 insertions(+) diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 6a0a8f1c7c90..fb0c394430c6 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -204,4 +204,8 @@ static inline bool cpu_mitigations_auto_nosmt(void) } #endif =20 +int arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __use= r *status); +int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long statu= s); +int arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long stat= us); + #endif /* _LINUX_CPU_H_ */ diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index 5c6080680cb2..6cd90460cbad 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -353,4 +353,31 @@ struct prctl_mm_map { */ #define PR_LOCK_SHADOW_STACK_STATUS 76 =20 +/* + * Get the current indirect branch tracking configuration for the current + * thread, this will be the value configured via PR_SET_INDIR_BR_LP_STATUS. + */ +#define PR_GET_INDIR_BR_LP_STATUS 77 + +/* + * Set the indirect branch tracking configuration. PR_INDIR_BR_LP_ENABLE w= ill + * enable cpu feature for user thread, to track all indirect branches and = ensure + * they land on arch defined landing pad instruction. + * x86 - If enabled, an indirect branch must land on `ENDBRANCH` instructi= on. + * arch64 - If enabled, an indirect branch must land on `BTI` instruction. + * riscv - If enabled, an indirect branch must land on `lpad` instruction. + * PR_INDIR_BR_LP_DISABLE will disable feature for user thread and indirect + * branches will no more be tracked by cpu to land on arch defined landing= pad + * instruction. + */ +#define PR_SET_INDIR_BR_LP_STATUS 78 +# define PR_INDIR_BR_LP_ENABLE (1UL << 0) + +/* + * Prevent further changes to the specified indirect branch tracking + * configuration. All bits may be locked via this call, including + * undefined bits. + */ +#define PR_LOCK_INDIR_BR_LP_STATUS 79 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/sys.c b/kernel/sys.c index cb366ff8703a..f347f3518d0b 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2336,6 +2336,21 @@ int __weak arch_lock_shadow_stack_status(struct task= _struct *t, unsigned long st return -EINVAL; } =20 +int __weak arch_get_indir_br_lp_status(struct task_struct *t, unsigned lon= g __user *status) +{ + return -EINVAL; +} + +int __weak arch_set_indir_br_lp_status(struct task_struct *t, unsigned lon= g status) +{ + return -EINVAL; +} + +int __weak arch_lock_indir_br_lp_status(struct task_struct *t, unsigned lo= ng status) +{ + return -EINVAL; +} + #define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE) =20 #ifdef CONFIG_ANON_VMA_NAME @@ -2811,6 +2826,21 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, a= rg2, unsigned long, arg3, return -EINVAL; error =3D arch_lock_shadow_stack_status(me, arg2); break; + case PR_GET_INDIR_BR_LP_STATUS: + if (arg3 || arg4 || arg5) + return -EINVAL; + error =3D arch_get_indir_br_lp_status(me, (unsigned long __user *)arg2); + break; + case PR_SET_INDIR_BR_LP_STATUS: + if (arg3 || arg4 || arg5) + return -EINVAL; + error =3D arch_set_indir_br_lp_status(me, arg2); + break; + case PR_LOCK_INDIR_BR_LP_STATUS: + if (arg3 || arg4 || arg5) + return -EINVAL; + error =3D arch_lock_indir_br_lp_status(me, arg2); + break; default: trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5); error =3D -EINVAL; --=20 2.43.0