[PATCH 4.14 091/138] x86/microcode: Do not upload microcode if CPUs are offline

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ashok Raj <ashok....@intel.com>

commit 30ec26da9967d0d785abc24073129a34c3211777 upstream.

Avoid loading microcode if any of the CPUs are offline, and issue a
warning. Having different microcode revisions on the system at any time
is outright dangerous.

[ Borislav: Massage changelog. ]

Signed-off-by: Ashok Raj <ashok....@intel.com>
Signed-off-by: Borislav Petkov <b...@suse.de>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Tested-by: Tom Lendacky <thomas.lenda...@amd.com>
Tested-by: Ashok Raj <ashok....@intel.com>
Reviewed-by: Tom Lendacky <thomas.lenda...@amd.com>
Cc: Arjan Van De Ven <arjan.van.de....@intel.com>
Link: 
http://lkml.kernel.org/r/1519352533-15992-4-git-send-email-ashok....@intel.com
Link: https://lkml.kernel.org/r/20180228102846.13447-5...@alien8.de
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 arch/x86/kernel/cpu/microcode/core.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -486,6 +486,16 @@ static void __exit microcode_dev_exit(vo
 /* fake device for request_firmware */
 static struct platform_device  *microcode_pdev;
 
+static int check_online_cpus(void)
+{
+       if (num_online_cpus() == num_present_cpus())
+               return 0;
+
+       pr_err("Not all CPUs online, aborting microcode update.\n");
+
+       return -EINVAL;
+}
+
 static enum ucode_state reload_for_cpu(int cpu)
 {
        struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
@@ -519,7 +529,13 @@ static ssize_t reload_store(struct devic
                return size;
 
        get_online_cpus();
+
+       ret = check_online_cpus();
+       if (ret)
+               goto put;
+
        mutex_lock(&microcode_mutex);
+
        for_each_online_cpu(cpu) {
                tmp_ret = reload_for_cpu(cpu);
                if (tmp_ret > UCODE_NFOUND) {
@@ -538,6 +554,8 @@ static ssize_t reload_store(struct devic
                microcode_check();
 
        mutex_unlock(&microcode_mutex);
+
+put:
        put_online_cpus();
 
        if (!ret)