kernel/SOURCES/1028-x86-microcode-Check-CPU-capabilities-after-late-micr.patch

From a8cd7508b4dfd8cedd394da8cdb0253f18bdb1a8 Mon Sep 17 00:00:00 2001
From: Ashok Raj <ashok.raj@intel.com>
Date: Mon, 9 Jan 2023 07:35:51 -0800
Subject: [PATCH 14/36] x86/microcode: Check CPU capabilities after late
 microcode update correctly

The kernel caches each CPU's feature bits at boot in an x86_capability[]
structure. However, the capabilities in the BSP's copy can be turned off
as a result of certain command line parameters or configuration
restrictions, for example the SGX bit. This can cause a mismatch when
comparing the values before and after the microcode update.

microcode_check() is called after an update to report any previously
cached CPUID bits which might have changed due to the update.

Therefore, store the cached CPU caps before the update and compare them
with the CPU caps after the microcode update has succeeded.

Thus, the comparison is done between the CPUID *hardware* bits before
and after the upgrade instead of using the cached, possibly runtime
modified values in BSP's boot_cpu_data copy.

As a result, false warnings about CPUID bits changes are avoided.

  [ bp:
  	- Massage.
	- Add SRBDS_CTRL example.
	- Add kernel-doc.
	- Incorporate forgotten review feedback from dhansen.
	]

Fixes: 1008c52c09dc ("x86/CPU: Add a microcode loader callback")
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230109153555.4986-3-ashok.raj@intel.com
(cherry picked from commit c0dd9245aa9e25a697181f6085692272c9ec61bc)

CVE: CVE-2023-20593
Signed-off-by: Mridula Shastry <mridula.c.shastry@oracle.com>
Reviewed-by: Todd Vierling <todd.vierling@oracle.com>
---
 arch/x86/include/asm/processor.h     |  1 +
 arch/x86/kernel/cpu/common.c         | 36 ++++++++++++++++++----------
 arch/x86/kernel/cpu/microcode/core.c |  6 +++++
 3 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9968d456d7e8..820104bdee1f 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -920,6 +920,7 @@ bool xen_set_default_idle(void);
 void stop_this_cpu(void *dummy);
 void df_debug(struct pt_regs *regs, long error_code);
 void microcode_check(struct cpuinfo_x86 *prev_info);
+void store_cpu_caps(struct cpuinfo_x86 *info);
 
 enum l1tf_mitigations {
 	L1TF_MITIGATION_OFF,
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 437fe55acce8..22763a691b7b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2146,6 +2146,25 @@ void cpu_init_secondary(void)
 #endif
 
 #ifdef CONFIG_MICROCODE_LATE_LOADING
+/**
+ * store_cpu_caps() - Store a snapshot of CPU capabilities
+ * @curr_info: Pointer where to store it
+ *
+ * Returns: None
+ */
+void store_cpu_caps(struct cpuinfo_x86 *curr_info)
+{
+	/* Reload CPUID max function as it might've changed. */
+	curr_info->cpuid_level = cpuid_eax(0);
+
+	/* Copy all capability leafs and pick up the synthetic ones. */
+	memcpy(&curr_info->x86_capability, &boot_cpu_data.x86_capability,
+	       sizeof(curr_info->x86_capability));
+
+	/* Get the hardware CPUID leafs */
+	get_cpu_cap(curr_info);
+}
+
 /**
  * microcode_check() - Check if any CPU capabilities changed after an update.
  * @prev_info:	CPU capabilities stored before an update.
@@ -2158,22 +2177,13 @@ void cpu_init_secondary(void)
  */
 void microcode_check(struct cpuinfo_x86 *prev_info)
 {
-	perf_check_microcode();
-
-	/* Reload CPUID max function as it might've changed. */
-	prev_info->cpuid_level = cpuid_eax(0);
+	struct cpuinfo_x86 curr_info;
 
-	/*
-	 * Copy all capability leafs to pick up the synthetic ones so that
-	 * memcmp() below doesn't fail on that. The ones coming from CPUID will
-	 * get overwritten in get_cpu_cap().
-	 */
-	memcpy(&prev_info->x86_capability, &boot_cpu_data.x86_capability,
-	       sizeof(prev_info->x86_capability));
+	perf_check_microcode();
 
-	get_cpu_cap(prev_info);
+	store_cpu_caps(&curr_info);
 
-	if (!memcmp(&prev_info->x86_capability, &boot_cpu_data.x86_capability,
+	if (!memcmp(&prev_info->x86_capability, &curr_info.x86_capability,
 		    sizeof(prev_info->x86_capability)))
 		return;
 
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 41a90074df21..9df2c40a4ddf 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -465,6 +465,12 @@ static int microcode_reload_late(void)
 	atomic_set(&late_cpus_in,  0);
 	atomic_set(&late_cpus_out, 0);
 
+	/*
+	 * Take a snapshot before the microcode update in order to compare and
+	 * check whether any bits changed after an update.
+	 */
+	store_cpu_caps(&prev_info);
+
 	ret = stop_machine_cpuslocked(__reload_late, NULL, cpu_online_mask);
 	if (ret == 0)
 		microcode_check(&prev_info);
-- 
2.39.3