Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759424Ab2FUMHY (ORCPT ); Thu, 21 Jun 2012 08:07:24 -0400 Received: from s15943758.onlinehome-server.info ([217.160.130.188]:51746 "EHLO mail.x86-64.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757127Ab2FUMHW (ORCPT ); Thu, 21 Jun 2012 08:07:22 -0400 From: Borislav Petkov To: X86-ML Cc: "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , LKML , Andreas Herrmann , Borislav Petkov , Henrique de Moraes Holschuh , Peter Zijlstra Subject: [PATCH -v2 1/2] x86, microcode: Sanitize per-cpu microcode reloading interface Date: Thu, 21 Jun 2012 14:07:16 +0200 Message-Id: <1340280437-7718-2-git-send-email-bp@amd64.org> X-Mailer: git-send-email 1.7.11.rc1 In-Reply-To: <1340280437-7718-1-git-send-email-bp@amd64.org> References: <1340280437-7718-1-git-send-email-bp@amd64.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2615 Lines: 88 From: Borislav Petkov 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. Cc: Henrique de Moraes Holschuh Cc: Peter Zijlstra Signed-off-by: Borislav Petkov --- arch/x86/kernel/microcode_core.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) diff --git a/arch/x86/kernel/microcode_core.c b/arch/x86/kernel/microcode_core.c index fbdfc6917180..24b852b61be3 100644 --- a/arch/x86/kernel/microcode_core.c +++ b/arch/x86/kernel/microcode_core.c @@ -298,19 +298,31 @@ static ssize_t reload_store(struct device *dev, 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; -- 1.7.11.rc1 -- 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/