[PATCH 4.9 106/107] x86/microcode: Do not upload microcode if CPUs are offline

[Greg Kroah-Hartman]

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

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

From: Ashok Raj <ashok.raj@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Tested-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Arjan Van De Ven <arjan.van.de.ven@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1519352533-15992-4-git-send-email-ashok.raj@xxxxxxxxx
Link: https://lkml.kernel.org/r/20180228102846.13447-5-bp@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 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
@@ -384,6 +384,16 @@ 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 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 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 != 0)
@@ -431,6 +447,8 @@ static ssize_t reload_store(struct devic
 	if (!ret)
 		perf_check_microcode();
 	mutex_unlock(&microcode_mutex);
+
+put:
 	put_online_cpus();
 
 	if (!ret)