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 B9A08474267; Wed, 12 Aug 2026 17:19:51 +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=1786555193; cv=none; b=ZKTGJs2+lNTqddXvNkVPsETkgFoUGvQIn/0sTXWN0MKEfetQKYPQkQpyq0b5NlQVGlKpH5vgm02ArhAaK+hyd4c5FbstwMRuM0F+DIcicbfr47SwfPapc7cRtv2CjzDogcIkZ8npyxUH/kBdiZ+4LgbwtbZSUVRqSWfQCrDXUEA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786555193; c=relaxed/simple; bh=i5iDbk7xspyU9JtWPxQanLp+P+TxFksfKMvwWQ0GNmU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=sFeLzVGt1F3s0rYcq2QvnVIt00CKjdehz4Y2RTB4aVAD3aNaEuSn1aW4Lh4iYfEFVVnzyRDjUFRMVGIevhOZWUUXo4iVmCJS+BJh1tHS14un6GJbz///yve3Iynb5vGuaWg238A2J7ABmXrNzWHHf0OJoFCaptOOGOsSk68Pdwk= 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=M6DHFVir; 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="M6DHFVir" 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 D295B1596; Wed, 12 Aug 2026 10:19:46 -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 B287F3F66F; Wed, 12 Aug 2026 10:19:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1786555190; bh=i5iDbk7xspyU9JtWPxQanLp+P+TxFksfKMvwWQ0GNmU=; h=From:To:Cc:Subject:Date:From; b=M6DHFVir0DQKQ3p3jdphqsuM/XS1GejEM6rjemttLZzudXUBL/Q6p8XmzkocZadC5 lPG8BN6/JCURoSKcrafIKBQCV9s59NrO7cokSBI5IOb3WKRC1cFftcEAAjTqmxoOkH f2dUbhJ6hcKKz7fl1NmgIRagL2bNzPvap5MRpakA= From: Bill Roberts To: "H. Peter Anvin" , Albert Ou , Alexandre Ghiti , Borislav Petkov , Dave Hansen , Ingo Molnar , Palmer Dabbelt , Paul Walmsley , rick.p.edgecombe@intel.com, Shuah Khan , Thomas Gleixner , x86@kernel.org Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-riscv@lists.infradead.org, Bill Roberts Subject: [PATCH v2 1/2] x86/shstk: support via prctl Date: Wed, 12 Aug 2026 12:19:39 -0500 Message-ID: <20260812171940.1046116-1-bill.roberts@arm.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: bpf@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 | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c index 0ca64900192f..c34ba3701dd0 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 +631,39 @@ bool shstk_is_enabled(void) { return features_enabled(ARCH_SHSTK_SHSTK); } + +#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK \ + (PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_WRITE | PR_SHADOW_STACK_PUSH) + +/* 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; + + if (status & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK) + return -EINVAL; + + /* 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); +} -- 2.55.0