raspi/linux
1
0
Fork 1
mirror of https://github.com/raspberrypi/linux.git synced 2025-12-06 18:09:56 +00:00
Code Issues Projects Releases Wiki Activity

x86, microcode: Sanitize per-cpu microcode reloading interface

Browse Source 
commit c9fc3f778a 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 <hmh@hmh.eng.br>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Link: http://lkml.kernel.org/r/1340280437-7718-2-git-send-email-bp@amd64.org
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Borislav Petkov
2012-06-21 14:07:16 +02:00
committed by Ben Hutchings
parent f7b867b55f
commit 87b98a1d1b
1 changed files with 19 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
arch/x86/kernel/microcode_core.c
View File

@@ -297,19 +297,31 @@ static ssize_t reload_store(struct sys_device *dev,
const char *buf, size_t size) const char *buf, size_t size)
{ {
unsigned long val; unsigned long val;
int cpu = dev->id; int cpu;
ssize_t ret = 0; 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); ret = kstrtoul(buf, 0, &val);
if (ret) if (ret)
return ret; return ret;
if (val == 1) { if (val != 1)
get_online_cpus(); return size;
if (cpu_online(cpu))
ret = reload_for_cpu(cpu); get_online_cpus();
put_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) if (!ret)
ret = size; ret = size;