x86/microcode: Taint and warn on late loading

mainline inclusion
from mainline-v5.19-rc1
commit d23d33ea
category: feature
feature: Backport Intel In Field Scan(IFS) multi-blob images support
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I6L337
CVE: N/A
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
commit/?id=d23d33ea

Intel-SIG: commit d23d33ea ("x86/microcode: Taint and warn on late loading")

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

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: NBorislav Petkov <bp@suse.de>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220525161232.14924-4-bp@alien8.deSigned-off-by: NAichun Shi <aichun.shi@intel.com>

arch/x86/kernel/cpu/microcode/core.c

@@ -510,6 +510,9 @@ 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);
 
@@ -558,6 +561,8 @@ static ssize_t reload_store(struct device *dev,
 	if (ret == 0)
 		ret = size;
 
+	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+
 	return ret;
 }