From 87b98a1d1bd63f002763b5cb153928d260850234 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Thu, 21 Jun 2012 14:07:16 +0200 Subject: [PATCH] x86, microcode: Sanitize per-cpu microcode reloading interface 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. Cc: Henrique de Moraes Holschuh Cc: Peter Zijlstra Signed-off-by: Borislav Petkov Link: http://lkml.kernel.org/r/1340280437-7718-2-git-send-email-bp@amd64.org Signed-off-by: H. Peter Anvin Signed-off-by: Ben Hutchings --- 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 19c7af1db1b1..29c95d753334 100644 --- 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_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; -- 2.39.5