x86/microcode: Do not access MSR_IA32_PLATFORM_ID when running as a guest

Patch in Fixes: causes the usual:

  unchecked MSR access error: RDMSR from 0x17 at ... (intel_get_platform_id)
  Call Trace:
   early_init_intel
   early_cpu_init
   setup_arch
   _printk
   start_kernel
   x86_64_start_reservations
   x86_64_start_kernel
   common_startup_64

because the kernel is booted in a guest.

In order to avoid it, this MSR access needs to be prevented when running
virtualized. That is usually done by checking X86_FEATURE_HYPERVISOR but
for this particular case it is too early yet.

The platform ID needs to be read as early as when microcode is loaded on
the BSP:

  load_ucode_bsp ... -> get_microcode_blob ... -> intel_find_matching_signature

and by that time, CPUID leafs haven't been parsed yet.

The microcode loader already has logic to check early whether the kernel
is running virtualized so make that globally available to arch/x86/. The
query whether running virtualized is getting more and more prominent in
recent times so might as well make it an arch-global var which the rest
of the code can use.

Fixes: d8630b67ca1ed ("x86/cpu: Add platform ID to CPU info structure")
Reported-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Tested-by: Binbin Wu <binbin.wu@linux.intel.com>
Link: https://lore.kernel.org/all/20260430020953.1405535-1-binbin.wu@linux.intel.com

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 10b5355b323e24af9e5ba07556a620200ee6dc12..67dd932305db5a1c44b114f022258aa2be3a6cd5 100644 (file)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -733,6 +733,7 @@ bool xen_set_default_idle(void);
 #endif
 
 void __noreturn stop_this_cpu(void *dummy);
+extern bool x86_hypervisor_present;
 void microcode_check(struct cpuinfo_x86 *prev_info);
 void store_cpu_caps(struct cpuinfo_x86 *info);
 

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index e533881284a12b9a0d6c5e9119703bbfbcaebafe..5c0afae75e9f6868d5cdd6d09a0e62c1da4111a2 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -322,7 +322,7 @@ static u32 get_patch_level(void)
 {
        u32 rev, dummy __always_unused;
 
-       if (IS_ENABLED(CONFIG_MICROCODE_DBG) && hypervisor_present) {
+       if (IS_ENABLED(CONFIG_MICROCODE_DBG) && x86_hypervisor_present) {
                int cpu = smp_processor_id();
 
                if (!microcode_rev[cpu]) {
@@ -714,7 +714,7 @@ static bool __apply_microcode_amd(struct microcode_amd *mc, u32 *cur_rev,
                        invlpg(p_addr_end);
        }
 
-       if (IS_ENABLED(CONFIG_MICROCODE_DBG) && hypervisor_present)
+       if (IS_ENABLED(CONFIG_MICROCODE_DBG) && x86_hypervisor_present)
                microcode_rev[smp_processor_id()] = mc->hdr.patch_id;
 
        /* verify patch application was successful */

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 651202e6fefbe4df4ff262b54157d09b1630b64f..45ca406a81124a0a64379efccde19ecf474cab61 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -57,7 +57,7 @@ bool force_minrev = IS_ENABLED(CONFIG_MICROCODE_LATE_FORCE_MINREV);
 u32 base_rev;
 u32 microcode_rev[NR_CPUS] = {};
 
-bool hypervisor_present;
+bool __ro_after_init x86_hypervisor_present;
 
 /*
  * Synchronization.
@@ -118,14 +118,9 @@ bool __init microcode_loader_disabled(void)
        /*
         * Disable when:
         *
-        * 1) The CPU does not support CPUID.
-        */
-       if (!cpuid_feature()) {
-               dis_ucode_ldr = true;
-               return dis_ucode_ldr;
-       }
-
-       /*
+        * 1) The CPU does not support CPUID, detected below in
+        *    load_ucode_bsp().
+        *
         * 2) Bit 31 in CPUID[1]:ECX is clear
         *    The bit is reserved for hypervisor use. This is still not
         *    completely accurate as XEN PV guests don't see that CPUID bit
@@ -135,9 +130,7 @@ bool __init microcode_loader_disabled(void)
         * 3) Certain AMD patch levels are not allowed to be
         *    overwritten.
         */
-       hypervisor_present = native_cpuid_ecx(1) & BIT(31);
-
-       if ((hypervisor_present && !IS_ENABLED(CONFIG_MICROCODE_DBG)) ||
+       if ((x86_hypervisor_present && !IS_ENABLED(CONFIG_MICROCODE_DBG)) ||
            amd_check_current_patch_level())
                dis_ucode_ldr = true;
 
@@ -179,6 +172,11 @@ void __init load_ucode_bsp(void)
 
        early_parse_cmdline();
 
+       if (!cpuid_feature())
+               dis_ucode_ldr = true;
+       else
+               x86_hypervisor_present = native_cpuid_ecx(1) & BIT(31);
+
        if (microcode_loader_disabled())
                return;
 

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 37ac4afe09724b1ef2f2c5254f4504cee77d74ed..a4c0a0cf928b4e75ae6fb033f5a09ad1a08ced86 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -138,6 +138,9 @@ u32 intel_get_platform_id(void)
 {
        unsigned int val[2];
 
+       if (x86_hypervisor_present)
+               return 0;
+
        /*
         * This can be called early. Use CPUID directly instead of
         * relying on cpuinfo_x86 which may not be fully initialized.

diff --git a/arch/x86/kernel/cpu/microcode/internal.h b/arch/x86/kernel/cpu/microcode/internal.h
index 3b93c0676b4fcc37591d2cf3b8d76858c64657b6..a10b547eda1e44560bbdba07b2f025d621879179 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/internal.h
+++ b/arch/x86/kernel/cpu/microcode/internal.h
@@ -48,7 +48,6 @@ extern struct early_load_data early_data;
 extern struct ucode_cpu_info ucode_cpu_info[];
 extern u32 microcode_rev[NR_CPUS];
 extern u32 base_rev;
-extern bool hypervisor_present;
 
 struct cpio_data find_microcode_in_initrd(const char *path);