From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 506C6494A14; Tue, 14 Jul 2026 15:48:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784044098; cv=none; b=l71F1yMxBlcKl1mQrB84qAORVBqduxdJu5NAihMkdhc+yYftjT+ca62XTrAhZYLVvH2bz1IRtUEe+vneMrV5N06zaa3tmASfWSoqkVJTesNyHBCYmXkdHmiiwMPNOLdYUCn8xA/ce8UbgqgQo1MdukjGFN9gKGxmvA+snItZ5j8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784044098; c=relaxed/simple; bh=AiaPVYwyyN7ONJ0y8wfnHDlaVFMqonq/XsnQGNf6ZJ0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HRhgVFO5EwFDiHRkCJ4QlYw97SL31LWkHHsUGu/nPng4MNAxiHH0MwH/ThLtnBj3+5d73AzZ4YK64vvj8DIrAHuLuZQ7kf5teoUAkO4V1qEXlgcUHP1Lz9b/FiUY/Jnzb5/2kyrIAvc+zryc0p5vybuqISdBt08sbh/gQ7fHTE8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=dvZqzeNL; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="dvZqzeNL" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D12D01477; Tue, 14 Jul 2026 08:48:08 -0700 (PDT) Received: from fedora (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6BF583FBB1; Tue, 14 Jul 2026 08:48:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1784044093; bh=AiaPVYwyyN7ONJ0y8wfnHDlaVFMqonq/XsnQGNf6ZJ0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dvZqzeNLPKEfdzv8EnOaSpzjeujtphTEaptqYk87kQ72nZ6dYV7CEhw1BR8r0RnGL FnSwM/EBRaojOwTF1UlVA045X1M64cy0c+YIz1i0cb7qmfoSUGI9DkHKIKH4y/FJLA T/5xCWJI5VnoDTFnbzVqfhEsIu81lbKqtZOnghAE= From: Bill Roberts To: "H. Peter Anvin" , Albert Ou , Alexandre Ghiti , Borislav Petkov , Dave Hansen , Ingo Molnar , Palmer Dabbelt , Paul Walmsley , Shuah Khan , Thomas Gleixner , x86@kernel.org Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-riscv@lists.infradead.org, Bill Roberts Subject: [PATCH 1/2] x86/shstk: support via prctl Date: Tue, 14 Jul 2026 10:47:39 -0500 Message-ID: <20260714154740.140431-2-bill.roberts@arm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260714154740.140431-1-bill.roberts@arm.com> References: <20260714154740.140431-1-bill.roberts@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Historically, managing the user-space shadow stack state on x86 has been handled exclusively through the arch_prctl() interface via the ARCH_SHSTK_* operations. However, other architectures (such as arm64 and riscv) do not implement arch_prctl() and instead utilize the newer, arch-agnostic, prctl() interface (i.e. PR_GET_SHADOW_STACK_STATUS and PR_SET_SHADOW_STACK_STATUS). To provide language runtimes, toolchains, and libc implementations with a consistent, cross-architecture interface for managing control-flow integrity, wire up the generic shadow stack prctl handlers for x86. Map the generic PR_SHADOW_STACK_ENABLE, PR_SHADOW_STACK_DISABLE, and PR_SHADOW_STACK_LOCK operations onto the underlying x86 internal CET helper routines. This allows portable userspace applications to toggle or query shadow stack states without relying on architecture-specific system calls, while maintaining backward compatibility with existing arch_prctl() calls. Signed-off-by: Bill Roberts --- arch/x86/kernel/shstk.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c index 0ca64900192f..ef3db94eec6a 100644 --- a/arch/x86/kernel/shstk.c +++ b/arch/x86/kernel/shstk.c @@ -18,6 +18,7 @@ #include #include #include +#include #include #include #include @@ -630,3 +631,37 @@ bool shstk_is_enabled(void) { return features_enabled(ARCH_SHSTK_SHSTK); } + +/* We assume the prctl() feature bits line up with the arch_prctl() specific ones. */ +static_assert(PR_SHADOW_STACK_ENABLE == ARCH_SHSTK_SHSTK); +static_assert(PR_SHADOW_STACK_WRITE == ARCH_SHSTK_WRSS); + +/* Handles the generic prctl interface for PR_SET_SHADOW_STACK_STATUS and its feature bits */ +int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status) +{ + int rc; + + /* x86 arch_prctl is single bit at a time, so handle these one at time */ + if (!status & PR_SHADOW_STACK_ENABLE) + return shstk_prctl(t, ARCH_SHSTK_DISABLE, ARCH_SHSTK_SHSTK); + + rc = shstk_prctl(t, ARCH_SHSTK_ENABLE, ARCH_SHSTK_SHSTK); + if (rc) + return rc; + + if (status & PR_SHADOW_STACK_WRITE) + return shstk_prctl(t, ARCH_SHSTK_ENABLE, ARCH_SHSTK_WRSS); + + return shstk_prctl(t, ARCH_SHSTK_DISABLE, ARCH_SHSTK_WRSS); +} + +/* Handles the generic prctl interface for PR_LOCK_SHADOW_STACK_STATUS and its feature bits */ +int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status) +{ + return shstk_prctl(t, ARCH_SHSTK_LOCK, status); +} + +int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *status) +{ + return shstk_prctl(t, ARCH_SHSTK_STATUS, (unsigned long)status); +} -- 2.54.0