Messages in this thread Patch in this message | | | Date | Fri, 15 Jun 2012 14:37:49 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge |
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Ok,
so at least Henrique and I feel that this per-core reloading interface is crap and it should go. Below is a first attempt to fix that. It is supposed to be a minimal fix so that it can be backported to stable.
I know, I know, it is not a fully stable-rules compatible patch but having in mind the stupidity of the interface and how dangerous it can be for users who want to shoot themselves in the foot with microcode, we better backport it everywhere we can.
So guys, please have a look and let me know of any objections.
It is lightly tested here and it seems to work.
Thanks.
From: Borislav Petkov <borislav.petkov@amd.com> Date: Fri, 15 Jun 2012 14:19:55 +0200 Subject: [PATCH] x86, microcode: Sanitize per-cpu microcode reloading interface
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
A more generic fix will follow.
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br> Cc: stable@vger.kernel.org Signed-off-by: Borislav Petkov <borislav.petkov@amd.com> --- 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
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