This is a note to let you know that I've just added the patch titled
x86, microcode: Sanitize per-cpu microcode reloading interface
to the 3.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-microcode-sanitize-per-cpu-microcode-reloading-interface.patch
and it can be found in the queue-3.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From c9fc3f778a6a215ace14ee556067c73982b6d40f Mon Sep 17 00:00:00 2001
From: Borislav Petkov <[email protected]>
Date: Thu, 21 Jun 2012 14:07:16 +0200
Subject: x86, microcode: Sanitize per-cpu microcode reloading interface
From: Borislav Petkov <[email protected]>
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 <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: H. Peter Anvin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
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
@@ -298,19 +298,31 @@ static ssize_t reload_store(struct devic
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;
Patches currently in stable-queue which might be from [email protected]
are
queue-3.5/x86-microcode-sanitize-per-cpu-microcode-reloading-interface.patch
queue-3.5/x86-mce-fix-siginfo_t-si_addr-value-for-non-recoverable-memory-faults.patch
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