From nobody Sun Feb 8 15:46:42 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 0EE7022D787 for ; Mon, 7 Apr 2025 12:47:00 +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=1744030022; cv=none; b=eZtARhbDTWCYTCWHdOqYB6X37W1TclkMjv6r3haDlmxM8g0nXAuSz3s5Pmc/S95tpq2iwTAEKXqaSy/pptQzKUQ/xmHDmmUmdRhxiT/kz1ORRk0T/OK+kHSTb64TdG1PTZYeqPBWnD9Pl9b1qa9wRgGSCVTTUq5hSVnFmOF32hY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744030022; c=relaxed/simple; bh=1OzazdeudmntwLk2IoCfuNvNbvQNsvI07peAdfRkaKE=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=bTpSceF9TB7TVSbzrhBohxmuUYdZh4Nx++5eBZ2oBT1LKxQn8MUP/yhZY5c8LDOCfd60XP27z3Opr6UEl0iBPS98FTEPGBLN1k4ORh6XsxbiXaQXBkzeSxhC0gu2pkSTbrX2nZhVk6W5sPkUKVGT85JbD+h4mbkYXxl3WlrMQfg= 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; 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 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 86404106F; Mon, 7 Apr 2025 05:47:01 -0700 (PDT) Received: from eglon.cambridge.arm.com (eglon.cambridge.arm.com [10.1.196.43]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B90DF3F694; Mon, 7 Apr 2025 05:46:58 -0700 (PDT) From: James Morse To: x86@kernel.org, linux-kernel@vger.kernel.org Cc: Tony Luck , Reinette Chatre , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , babu.moger@amd.com, James Morse , Sebastian Andrzej Siewior Subject: [PATCH] x86/resctrl: Fix rdtgroup_mkdir()'s unlocked use of kernfs_node::name Date: Mon, 7 Apr 2025 13:46:37 +0100 Message-Id: <20250407124637.2433230-1-james.morse@arm.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250213145023.2820193-7-bigeasy@linutronix.de> References: <20250213145023.2820193-7-bigeasy@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Since commit 741c10b096bc ("kernfs: Use RCU to access kernfs_node::name."), a helper rdt_kn_name() that checks that rdtgroup_mutex is held has been used for all accesses to the kernfs node name. rdtgroup_mkdir() uses the name to determine if a valid monitor group is being created by checking the parent name is "mon_groups". This is done without holding rdtgroup_mutex, and now triggers the following warning: | WARNING: suspicious RCU usage | 6.15.0-rc1 #4465 Tainted: G E | ----------------------------- | arch/x86/kernel/cpu/resctrl/internal.h:408 suspicious rcu_dereference_che= ck() usage! [...] | Call Trace: | | dump_stack_lvl+0x6c/0xa0 | lockdep_rcu_suspicious.cold+0x4e/0x96 | is_mon_groups+0xba/0xd0 | rdtgroup_mkdir+0x118/0x1970 | kernfs_iop_mkdir+0xfa/0x1a0 | vfs_mkdir+0x456/0x760 | do_mkdirat+0x257/0x310 | __x64_sys_mkdir+0xd4/0x120 | do_syscall_64+0x6d/0x150 | entry_SYSCALL_64_after_hwframe+0x76/0x7e Creating a control or monitor group calls mkdir_rdt_prepare(), which uses rdtgroup_kn_lock_live() to take the rdtgroup_mutex. To avoid taking and dropping the lock, move the check for the monitor group name and position into mkdir_rdt_prepare() so that it occurs under rdtgroup_mutex. Hoist is_mon_groups() earlier in the file. CC: Sebastian Andrzej Siewior Fixes: 741c10b096bc ("kernfs: Use RCU to access kernfs_node::name.") Signed-off-by: James Morse Reviewed-by: Reinette Chatre --- arch/x86/kernel/cpu/resctrl/rdtgroup.c | 48 +++++++++++++++----------- 1 file changed, 27 insertions(+), 21 deletions(-) diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/r= esctrl/rdtgroup.c index 93ec829015f1..a81a42cf6656 100644 --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c @@ -3553,6 +3553,22 @@ static void mkdir_rdt_prepare_rmid_free(struct rdtgr= oup *rgrp) free_rmid(rgrp->closid, rgrp->mon.rmid); } =20 +/* + * We allow creating mon groups only with in a directory called "mon_group= s" + * which is present in every ctrl_mon group. Check if this is a valid + * "mon_groups" directory. + * + * 1. The directory should be named "mon_groups". + * 2. The mon group itself should "not" be named "mon_groups". + * This makes sure "mon_groups" directory always has a ctrl_mon group + * as parent. + */ +static bool is_mon_groups(struct kernfs_node *kn, const char *name) +{ + return (!strcmp(rdt_kn_name(kn), "mon_groups") && + strcmp(name, "mon_groups")); +} + static int mkdir_rdt_prepare(struct kernfs_node *parent_kn, const char *name, umode_t mode, enum rdt_group_type rtype, struct rdtgroup **r) @@ -3568,6 +3584,15 @@ static int mkdir_rdt_prepare(struct kernfs_node *par= ent_kn, goto out_unlock; } =20 + /* + * Check the parent directory for a monitor group is a "mon_groups" + * directory. + */ + if (rtype =3D=3D RDTMON_GROUP && !is_mon_groups(parent_kn, name)) { + ret =3D -EPERM; + goto out_unlock; + } + if (rtype =3D=3D RDTMON_GROUP && (prdtgrp->mode =3D=3D RDT_MODE_PSEUDO_LOCKSETUP || prdtgrp->mode =3D=3D RDT_MODE_PSEUDO_LOCKED)) { @@ -3751,22 +3776,6 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_nod= e *parent_kn, return ret; } =20 -/* - * We allow creating mon groups only with in a directory called "mon_group= s" - * which is present in every ctrl_mon group. Check if this is a valid - * "mon_groups" directory. - * - * 1. The directory should be named "mon_groups". - * 2. The mon group itself should "not" be named "mon_groups". - * This makes sure "mon_groups" directory always has a ctrl_mon group - * as parent. - */ -static bool is_mon_groups(struct kernfs_node *kn, const char *name) -{ - return (!strcmp(rdt_kn_name(kn), "mon_groups") && - strcmp(name, "mon_groups")); -} - static int rdtgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode) { @@ -3782,11 +3791,8 @@ static int rdtgroup_mkdir(struct kernfs_node *parent= _kn, const char *name, if (resctrl_arch_alloc_capable() && parent_kn =3D=3D rdtgroup_default.kn) return rdtgroup_mkdir_ctrl_mon(parent_kn, name, mode); =20 - /* - * If RDT monitoring is supported and the parent directory is a valid - * "mon_groups" directory, add a monitoring subdirectory. - */ - if (resctrl_arch_mon_capable() && is_mon_groups(parent_kn, name)) + /* Else, attempt to add a monitoring subdirectory. */ + if (resctrl_arch_mon_capable()) return rdtgroup_mkdir_mon(parent_kn, name, mode); =20 return -EPERM; --=20 2.39.5