From mboxrd@z Thu Jan 1 00:00:00 1970 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7272BC77B75 for ; Tue, 23 May 2023 19:55:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238402AbjEWTzp (ORCPT ); Tue, 23 May 2023 15:55:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229614AbjEWTzl (ORCPT ); Tue, 23 May 2023 15:55:41 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2CE4129 for ; Tue, 23 May 2023 12:54:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1684871694; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zNmXH+90JUJ7ZzD9zSZr+aTZro/+2dtu4Fp8oSsNfvs=; b=BSOyJRD/zwXd2VX9CnBo/WC47P3Z38+VocoHNrQyrXFPlKJFhdvg4YqL6xCyXKzf1PdxMy KGTTIA4/sw/XqszD54XGU7NCihKgJ+2zRajX30259OlV4iDjAN/YS+OqunMlKGFUsJcELe WKI8AlY66RsxsdBJjLYuFShy/+ZsKQE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-348-PRxfwqV2MESvbc8Age1qzg-1; Tue, 23 May 2023 15:54:50 -0400 X-MC-Unique: PRxfwqV2MESvbc8Age1qzg-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 34D10185A78B; Tue, 23 May 2023 19:54:50 +0000 (UTC) Received: from work.redhat.com (unknown [10.39.193.140]) by smtp.corp.redhat.com (Postfix) with ESMTP id DA612492B00; Tue, 23 May 2023 19:54:48 +0000 (UTC) From: Tim Wiederhake To: "Borislav Petkov" , "Dave Hansen" , "H. Peter Anvin" , "Ingo Molnar" , "Paolo Bonzini" , "Thomas Gleixner" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org Cc: Tim Wiederhake Subject: [PATCH 2/2] x86/msr: Allow unprivileged read access to some MSRs Date: Tue, 23 May 2023 21:49:49 +0200 Message-Id: <20230523194949.96149-2-twiederh@redhat.com> In-Reply-To: <20230523194949.96149-1-twiederh@redhat.com> References: <20230523194949.96149-1-twiederh@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Delaying access control allows unprivileged processes to read specific MSRs, such as IA32_CORE_CAPABILITIES and IA32_ARCH_CAPABILITIES. This is helpful for e.g. qemu and libvirt who require the raw MSR content to calculate host CPU capabilities. Other programs might be interested in IA32_EFER for x86-64-v1 detection. Signed-off-by: Tim Wiederhake --- arch/x86/kernel/msr.c | 38 +++++++++++++++++++++++++++++++++----- 1 file changed, 33 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c index 058f2b67d0c7..9485aa7f8161 100644 --- a/arch/x86/kernel/msr.c +++ b/arch/x86/kernel/msr.c @@ -50,6 +50,23 @@ enum allow_write_msrs { static enum allow_write_msrs allow_writes = MSR_WRITES_DEFAULT; +static int filter_read(struct file *file, u32 reg) +{ + if (file->private_data) + return 0; + + switch (reg) { + case MSR_IA32_CORE_CAPS: + case MSR_IA32_ARCH_CAPABILITIES: + case MSR_EFER: + return 0; + default: + break; + } + + return -EPERM; +} + static ssize_t msr_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) { @@ -59,6 +76,10 @@ static ssize_t msr_read(struct file *file, char __user *buf, int cpu = iminor(file_inode(file)); int err = 0; + err = filter_read(file, reg); + if (err) + return err; + if (count < 8) return -EINVAL; /* Invalid chunk size */ @@ -71,7 +92,7 @@ static ssize_t msr_read(struct file *file, char __user *buf, return 8; } -static int filter_write(u32 reg) +static int filter_write(struct file *file, u32 reg) { /* * MSRs writes usually happen all at once, and can easily saturate kmsg. @@ -83,6 +104,9 @@ static int filter_write(u32 reg) */ static DEFINE_RATELIMIT_STATE(fw_rs, 30 * HZ, 1); + if (!file->private_data) + return -EPERM; + switch (allow_writes) { case MSR_WRITES_ON: return 0; case MSR_WRITES_OFF: return -EPERM; @@ -113,7 +137,7 @@ static ssize_t msr_write(struct file *file, const char __user *buf, if (err) return err; - err = filter_write(reg); + err = filter_write(file, reg); if (err) return err; @@ -156,6 +180,9 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg) err = -EFAULT; break; } + err = filter_read(file, regs[1]); + if (err) + return err; err = rdmsr_safe_regs_on_cpu(cpu, regs); if (err) break; @@ -176,7 +203,7 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg) if (err) break; - err = filter_write(regs[1]); + err = filter_write(file, regs[1]); if (err) return err; @@ -202,8 +229,7 @@ static int msr_open(struct inode *inode, struct file *file) unsigned int cpu = iminor(file_inode(file)); struct cpuinfo_x86 *c; - if (!capable(CAP_SYS_RAWIO)) - return -EPERM; + file->private_data = (void *)(capable(CAP_SYS_RAWIO)); if (cpu >= nr_cpu_ids || !cpu_online(cpu)) return -ENXIO; /* No such CPU */ @@ -245,6 +271,8 @@ static int msr_device_destroy(unsigned int cpu) static char *msr_devnode(const struct device *dev, umode_t *mode) { + if (mode) + *mode = 0644; return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt)); } -- 2.39.2