linux-kernel - [RFC PATCH -v2] x86/microcode: Taint and warn on late loading

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Date:   Wed, 25 May 2022 14:52:20 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH -v2] x86/microcode: Taint and warn on late loading

On Wed, May 25, 2022 at 12:03:52PM +0200, Peter Zijlstra wrote:
> Should we not warn *before* attempting the ucode update? Should the
> whole thing come unstuck, you at least have some clue.

Sure.

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

Warn before it is attempted and taint the kernel.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/microcode/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index c717db6b6856..801b44ac3851 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 @@ 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

-- 
Regards/Gruss,
    Boris.

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