x86/microcode: Do not upload microcode if CPUs are offline

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.raj@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Tested-by: Ashok Raj <ashok.raj@intel.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Arjan Van De Ven <arjan.van.de.ven@intel.com>
Link: http://lkml.kernel.org/r/1519352533-15992-4-git-send-email-ashok.raj@intel.com
Link: https://lkml.kernel.org/r/20180228102846.13447-5-bp@alien8.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 0afaf00..2da1c6a 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -384,6 +384,16 @@ static void __exit microcode_dev_exit(void)
 /* 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 int reload_for_cpu(int cpu)
 {
        struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
@@ -418,7 +428,13 @@ static ssize_t reload_store(struct device *dev,
                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 != 0)
@@ -431,6 +447,8 @@ static ssize_t reload_store(struct device *dev,
        if (!ret)
                perf_check_microcode();
        mutex_unlock(&microcode_mutex);
+
+put:
        put_online_cpus();
 
        if (!ret)