linux-kernel - [RFC PATCH 3/3] x86/microcode: Taint and warn on late loading

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Date:   Tue, 24 May 2022 20:53:24 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 3/3] x86/microcode: Taint and warn on late loading

From: Borislav Petkov <bp@...e.de>

Warn when done and taint the kernel.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/microcode/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index c717db6b6856..f7ded2facaa0 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -501,6 +501,8 @@ static int microcode_reload_late(void)
 		microcode_check();
 
 	pr_info("Reload completed, microcode revision: 0x%x\n", boot_cpu_data.microcode);
+	pr_err("However, late loading is dangerous and it taints the kernel.\n"
+	       "You should switch to early loading, if possible.\n");
 
 	return ret;
 }
@@ -541,6 +543,8 @@ 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;
 }
 
-- 
2.35.1