From: Borislav Petkov <bp@suse.de>
Date: Wed, 25 May 2022 16:12:31 +0000 (+0200)
Subject: x86/microcode: Taint and warn on late loading
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=d23d33ea0fcdc4bbb484990bf53867f99c63ccab;p=linux.git

x86/microcode: Taint and warn on late loading

Warn before it is attempted and taint the kernel. Late loading microcode
can lead to malfunction of the kernel when the microcode update changes
behaviour. There is no way for the kernel to determine whether its safe or
not.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220525161232.14924-4-bp@alien8.de
---

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index c717db6b6856d..801b44ac38514 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -493,6 +493,9 @@ static int microcode_reload_late(void)
 {
 	int ret;
 
+	pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n");
+	pr_err("You should switch to early loading, if possible.\n");
+
 	atomic_set(&late_cpus_in,  0);
 	atomic_set(&late_cpus_out, 0);
 
@@ -541,6 +544,8 @@ put:
 	if (ret == 0)
 		ret = size;
 
+	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+
 	return ret;
 }