Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754943Ab2HMWF2 (ORCPT ); Mon, 13 Aug 2012 18:05:28 -0400 Received: from mail-gg0-f174.google.com ([209.85.161.174]:60176 "EHLO mail-gg0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754790Ab2HMWFY (ORCPT ); Mon, 13 Aug 2012 18:05:24 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg KH , torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Borislav Petkov , Henrique de Moraes Holschuh , Peter Zijlstra , "H. Peter Anvin" Subject: [ 36/44] x86, microcode: Sanitize per-cpu microcode reloading interface Date: Mon, 13 Aug 2012 15:02:43 -0700 Message-Id: <20120813220145.337264645@linuxfoundation.org> X-Mailer: git-send-email 1.7.10.1.362.g242cab3 In-Reply-To: <20120813220142.113186818@linuxfoundation.org> References: <20120813220142.113186818@linuxfoundation.org> User-Agent: quilt/0.60-20.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2862 Lines: 97 From: Greg KH 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Borislav Petkov commit c9fc3f778a6a215ace14ee556067c73982b6d40f upstream. Microcode reloading in a per-core manner is a very bad idea for both major x86 vendors. And the thing is, we have such interface with which we can end up with different microcode versions applied on different cores of an otherwise homogeneous wrt (family,model,stepping) system. So turn off the possibility of doing that per core and allow it only system-wide. This is a minimal fix which we'd like to see in stable too thus the more-or-less arbitrary decision to allow system-wide reloading only on the BSP: $ echo 1 > /sys/devices/system/cpu/cpu0/microcode/reload ... and disable the interface on the other cores: $ echo 1 > /sys/devices/system/cpu/cpu23/microcode/reload -bash: echo: write error: Invalid argument Also, allowing the reload only from one CPU (the BSP in that case) doesn't allow the reload procedure to degenerate into an O(n^2) deal when triggering reloads from all /sys/devices/system/cpu/cpuX/microcode/reload sysfs nodes simultaneously. A more generic fix will follow. Signed-off-by: Borislav Petkov Cc: Henrique de Moraes Holschuh Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1340280437-7718-2-git-send-email-bp@amd64.org Signed-off-by: H. Peter Anvin Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/microcode_core.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) --- a/arch/x86/kernel/microcode_core.c +++ b/arch/x86/kernel/microcode_core.c @@ -297,19 +297,31 @@ static ssize_t reload_store(struct sys_d const char *buf, size_t size) { unsigned long val; - int cpu = dev->id; - ssize_t ret = 0; + int cpu; + ssize_t ret = 0, tmp_ret; + + /* allow reload only from the BSP */ + if (boot_cpu_data.cpu_index != dev->id) + return -EINVAL; ret = kstrtoul(buf, 0, &val); if (ret) return ret; - if (val == 1) { - get_online_cpus(); - if (cpu_online(cpu)) - ret = reload_for_cpu(cpu); - put_online_cpus(); + if (val != 1) + return size; + + get_online_cpus(); + for_each_online_cpu(cpu) { + tmp_ret = reload_for_cpu(cpu); + if (tmp_ret != 0) + pr_warn("Error reloading microcode on CPU %d\n", cpu); + + /* save retval of the first encountered reload error */ + if (!ret) + ret = tmp_ret; } + put_online_cpus(); if (!ret) ret = size; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/