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

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Date:   Tue, 14 Aug 2018 19:18:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ashok Raj <ashok.raj@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH 4.9 106/107] x86/microcode: Do not upload microcode if CPUs are offline

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

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

From: Ashok Raj <ashok.raj@...el.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.raj@...el.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Tom Lendacky <thomas.lendacky@....com>
Tested-by: Ashok Raj <ashok.raj@...el.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
Cc: Arjan Van De Ven <arjan.van.de.ven@...el.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@...uxfoundation.org>
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -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)