Semantics of the microcode reload file are only defined if a "1" is
written. But the code silently treats any other unsigned integer as a
successful write even though no actions are performed to load microcode.

Report those erroneous writes back to user.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: x86 <x86@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Thomas Gleixner (Intel) <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Stefan Talpalaru <stefantalpalaru@yahoo.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Peter Zilstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Cooper <Andrew.Cooper3@citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Martin Pohlack <mpohlack@amazon.de>
---
 arch/x86/kernel/cpu/microcode/core.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 1c6831b8b244..e4b4dfcf2d18 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -476,11 +476,8 @@ static ssize_t reload_store(struct device *dev,
 	ssize_t ret;
 
 	ret = kstrtoul(buf, 0, &val);
-	if (ret)
-		return ret;
-
-	if (val != 1)
-		return size;
+	if (ret || val != 1)
+		return -EINVAL;
 
 	cpus_read_lock();
 
-- 
2.37.2

The following commit has been merged into the x86/microcode branch of tip:

Commit-ID:     25d0dc4b957cc8674f8554e85f18a00467e876d7
Gitweb:        https://git.kernel.org/tip/25d0dc4b957cc8674f8554e85f18a00467e876d7
Author:        Ashok Raj <ashok.raj@intel.com>
AuthorDate:    Mon, 30 Jan 2023 13:39:48 -08:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 31 Jan 2023 16:47:03 +01:00

x86/microcode: Allow only "1" as a late reload trigger value

Microcode gets reloaded late only if "1" is written to the reload file.
However, the code silently treats any other unsigned integer as a
successful write even though no actions are performed to load microcode.

Make the loader more strict to accept only "1" as a trigger value and
return an error otherwise.

  [ bp: Massage commit message. ]

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230130213955.6046-3-ashok.raj@intel.com
---
 arch/x86/kernel/cpu/microcode/core.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 61d57d9..fdd1e7e 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -475,11 +475,8 @@ static ssize_t reload_store(struct device *dev,
 	ssize_t ret = 0;
 
 	ret = kstrtoul(buf, 0, &val);
-	if (ret)
-		return ret;
-
-	if (val != 1)
-		return size;
+	if (ret || val != 1)
+		return -EINVAL;
 
 	cpus_read_lock();