linux-kernel - [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if microcode loading was successful

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Message-Id: <20230130213955.6046-2-ashok.raj@intel.com>
Date:   Mon, 30 Jan 2023 13:39:47 -0800
From:   Ashok Raj <ashok.raj@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ashok Raj <ashok.raj@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Stefan Talpalaru <stefantalpalaru@...oo.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Jonathan Corbet <corbet@....net>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Peter Zilstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Martin Pohlack <mpohlack@...zon.de>
Subject: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if microcode loading was successful

Currently when late loading is aborted due to check_online_cpu(), kernel
still ends up tainting the kernel.

Taint only when microcode loading was successful.

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ashok Raj <ashok.raj@...el.com>
Cc: LKML <linux-kernel@...r.kernel.org>
Cc: x86 <x86@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Alison Schofield <alison.schofield@...el.com>
Cc: Reinette Chatre <reinette.chatre@...el.com>
Cc: Thomas Gleixner (Intel) <tglx@...utronix.de>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Stefan Talpalaru <stefantalpalaru@...oo.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Jonathan Corbet <corbet@....net>
Cc: Rafael J. Wysocki <rafael@...nel.org>
Cc: Peter Zilstra (Intel) <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Andrew Cooper <Andrew.Cooper3@...rix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Martin Pohlack <mpohlack@...zon.de>
---
v1->v2: (Thomas)
	- Remove unnecessary assignment of ret that's being overwritten.
	- Taint kernel only of loading was successful
---
 arch/x86/kernel/cpu/microcode/core.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 61d57d9b93ee..1c6831b8b244 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -472,7 +472,8 @@ static ssize_t reload_store(struct device *dev,
 	enum ucode_state tmp_ret = UCODE_OK;
 	int bsp = boot_cpu_data.cpu_index;
 	unsigned long val;
-	ssize_t ret = 0;
+	int load_ret = -1;
+	ssize_t ret;
 
 	ret = kstrtoul(buf, 0, &val);
 	if (ret)
@@ -488,20 +489,26 @@ static ssize_t reload_store(struct device *dev,
 		goto put;
 
 	tmp_ret = microcode_ops->request_microcode_fw(bsp, &microcode_pdev->dev);
-	if (tmp_ret != UCODE_NEW)
+	if (tmp_ret != UCODE_NEW) {
+		ret = size;
 		goto put;
+	}
 
 	mutex_lock(&microcode_mutex);
-	ret = microcode_reload_late();
+	load_ret = microcode_reload_late();
 	mutex_unlock(&microcode_mutex);
 
 put:
 	cpus_read_unlock();
 
-	if (ret == 0)
+	/*
+	 * Taint only when loading was successful
+	 */
+	if (load_ret == 0) {
 		ret = size;
-
-	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+		pr_warn("Microcode late loading tainted the kernel\n");
+	}
 
 	return ret;
 }
-- 
2.37.2