Re: [PATCH] x86/microcode: Fix crashes on early 486 CPUs due to usage of 'cpuid'.

[Borislav Petkov <bp@alien8.de>]

On Sun, Apr 06, 2025 at 05:46:33PM +1000, Kevin Koster wrote:
> But if I move "cpuid_1_eax = native_cpuid_eax(1);" to after the
> microcode_loader_disabled() check in amd.c, like in the first patch, it
> boots fine!

Yeah, I noticed that too last night. Here's a hopefully better version after
I ran it on my 32-bit Atom - I don't have your old rust and maybe you should
simply throw it in the garbage - that thing is probably not worth the
electricity it uses to power up... :-)

Anyway, I wanna do this below.

The only hunk I'm not sure about is in mk_early_pgtbl_32() because I don't
want to uglify the loader checking code with __pa* macros just so that initrd
mapping is made conditional on whether the loader is enabled.

After all, zap_early_initrd_mapping() clears it right after there.

But let's see what tglx says as this is his code:

4c585af7180c ("x86/boot/32: Temporarily map initrd for microcode loading")

Thx.

diff --git a/arch/x86/include/asm/microcode.h b/arch/x86/include/asm/microcode.h
index 695e569159c1..d53148fb893a 100644
--- a/arch/x86/include/asm/microcode.h
+++ b/arch/x86/include/asm/microcode.h
@@ -17,10 +17,12 @@ struct ucode_cpu_info {
 void load_ucode_bsp(void);
 void load_ucode_ap(void);
 void microcode_bsp_resume(void);
+bool __init microcode_loader_disabled(void);
 #else
 static inline void load_ucode_bsp(void)	{ }
 static inline void load_ucode_ap(void) { }
 static inline void microcode_bsp_resume(void) { }
+bool __init microcode_loader_disabled(void) { return false; }
 #endif
 
 extern unsigned long initrd_start_early;
diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index b61028cf5c8a..dda7f0d409e9 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -1099,7 +1099,7 @@ static int __init save_microcode_in_initrd(void)
 	enum ucode_state ret;
 	struct cpio_data cp;
 
-	if (dis_ucode_ldr || c->x86_vendor != X86_VENDOR_AMD || c->x86 < 0x10)
+	if (microcode_loader_disabled() || c->x86_vendor != X86_VENDOR_AMD || c->x86 < 0x10)
 		return 0;
 
 	if (!find_blobs_in_containers(&cp))
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index b3658d11e7b6..b6125149894b 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -42,7 +42,7 @@
 #include "internal.h"
 
 static struct microcode_ops	*microcode_ops;
-bool dis_ucode_ldr = true;
+static int dis_ucode_ldr = -1;
 
 bool force_minrev = IS_ENABLED(CONFIG_MICROCODE_LATE_FORCE_MINREV);
 module_param(force_minrev, bool, S_IRUSR | S_IWUSR);
@@ -95,11 +95,20 @@ static bool amd_check_current_patch_level(void)
 	return false;
 }
 
-static bool __init check_loader_disabled_bsp(void)
+bool __init microcode_loader_disabled(void)
 {
-	static const char *__dis_opt_str = "dis_ucode_ldr";
-	const char *cmdline = boot_command_line;
-	const char *option  = __dis_opt_str;
+	if (dis_ucode_ldr < 0) {
+		if (cmdline_find_option_bool(boot_command_line, "dis_ucode_ldr") <= 0)
+			dis_ucode_ldr = 0;
+		else
+			goto disable;
+	}
+
+	if (dis_ucode_ldr > 0)
+		return true;
+
+	if (!have_cpuid_p())
+		goto disable;
 
 	/*
 	 * CPUID(1).ECX[31]: reserved for hypervisor use. This is still not
@@ -107,17 +116,18 @@ static bool __init check_loader_disabled_bsp(void)
 	 * that's good enough as they don't land on the BSP path anyway.
 	 */
 	if (native_cpuid_ecx(1) & BIT(31))
-		return true;
+		goto disable;
 
 	if (x86_cpuid_vendor() == X86_VENDOR_AMD) {
 		if (amd_check_current_patch_level())
-			return true;
+			goto disable;
 	}
 
-	if (cmdline_find_option_bool(cmdline, option) <= 0)
-		dis_ucode_ldr = false;
+	return (bool)dis_ucode_ldr;
 
-	return dis_ucode_ldr;
+disable:
+	dis_ucode_ldr = 1;
+	return true;
 }
 
 void __init load_ucode_bsp(void)
@@ -125,7 +135,7 @@ void __init load_ucode_bsp(void)
 	unsigned int cpuid_1_eax;
 	bool intel = true;
 
-	if (!have_cpuid_p())
+	if (microcode_loader_disabled())
 		return;
 
 	cpuid_1_eax = native_cpuid_eax(1);
@@ -146,9 +156,6 @@ void __init load_ucode_bsp(void)
 		return;
 	}
 
-	if (check_loader_disabled_bsp())
-		return;
-
 	if (intel)
 		load_ucode_intel_bsp(&early_data);
 	else
@@ -810,7 +817,7 @@ static int __init microcode_init(void)
 	struct cpuinfo_x86 *c = &boot_cpu_data;
 	int error;
 
-	if (dis_ucode_ldr)
+	if (microcode_loader_disabled())
 		return -EINVAL;
 
 	if (c->x86_vendor == X86_VENDOR_INTEL)
diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 819199bc0119..2a397da43923 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -389,7 +389,7 @@ static int __init save_builtin_microcode(void)
 	if (xchg(&ucode_patch_va, NULL) != UCODE_BSP_LOADED)
 		return 0;
 
-	if (dis_ucode_ldr || boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
+	if (microcode_loader_disabled() || boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
 		return 0;
 
 	uci.mc = get_microcode_blob(&uci, true);
diff --git a/arch/x86/kernel/cpu/microcode/internal.h b/arch/x86/kernel/cpu/microcode/internal.h
index 5df621752fef..50a9702ae4e2 100644
--- a/arch/x86/kernel/cpu/microcode/internal.h
+++ b/arch/x86/kernel/cpu/microcode/internal.h
@@ -94,7 +94,6 @@ static inline unsigned int x86_cpuid_family(void)
 	return x86_family(eax);
 }
 
-extern bool dis_ucode_ldr;
 extern bool force_minrev;
 
 #ifdef CONFIG_CPU_SUP_AMD
diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
index de001b2146ab..375f2d7f1762 100644
--- a/arch/x86/kernel/head32.c
+++ b/arch/x86/kernel/head32.c
@@ -145,10 +145,6 @@ void __init __no_stack_protector mk_early_pgtbl_32(void)
 	*ptr = (unsigned long)ptep + PAGE_OFFSET;
 
 #ifdef CONFIG_MICROCODE_INITRD32
-	/* Running on a hypervisor? */
-	if (native_cpuid_ecx(1) & BIT(31))
-		return;
-
 	params = (struct boot_params *)__pa_nodebug(&boot_params);
 	if (!params->hdr.ramdisk_size || !params->hdr.ramdisk_image)
 		return;


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette