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

[Kevin Koster <lkml@ombertech.com>]

On Mon, 7 Apr 2025 12:29:27 +0200
Borislav Petkov <bp@alien8.de> wrote:

> On Mon, Apr 07, 2025 at 09:58:48AM +1000, Kevin Koster wrote:
> > But I like to know Linux really works on the hardware it's built
> > for,
> 
> I don't know what that means.

To rephrase: I like knowing that "CONFIG_M486=y" works, in the kernel
configuration. If not, then I know to use other OSs if I want to boot a
486.

> > and I'm not much better, writing this now on a Pentium 1.
> 
> Lemme guess: this is your main machine you use for daily work?

For email/news every morning, then a (newer) laptop afterwards.

> > > -	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;
> > 
> > Still fails unless the native_cpuid_eax(1) call is moved under
> > here. After that change, it boots fine.
> 
> Please show me with a diff what you're doing because I don't know
> what you mean.

OK, this is the change I made after applying your patch:

--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -1093,7 +1093,7 @@
 
 static int __init save_microcode_in_initrd(void)
 {
-	unsigned int cpuid_1_eax = native_cpuid_eax(1);
+	unsigned int cpuid_1_eax;
	struct cpuinfo_x86 *c = &boot_cpu_data;
	struct cont_desc desc = { 0 };
	enum ucode_state ret;
@@ -1102,6 +1102,8 @@
	if (microcode_loader_disabled() || c->x86_vendor != X86_VENDOR_AMD || c->x86 < 0x10)
		return 0;
 
+	cpuid_1_eax = native_cpuid_eax(1);
+
	if (!find_blobs_in_containers(&cp))
		return -EINVAL;

> I did this:
> 
> bool have_cpuid_p(void)
> {
>         return false;
> }
> 
> in order to simulate no CPUID support but my 32-bit guest boots fine.

It's detecting no CPUID support on 486 CPUs OK, however
save_microcode_in_initrd() uses CPUID before checking if it is
supported.

> Also, send a full dmesg from that machine so that I can try to
> reproduce here.

This is with your latest patch applied, without my above change:

No EFI environment detected.
early console in extract_kernel
input_data: 0x007d1094
input_len: 0x005aa603
output: 0x00100000
output_len: 0x00bb42d8
kernel_total_size: 0x00c9a000
needed_size: 0x00c9a000

Decompressing Linux... Parsing ELF... No relocation needed... done.
Booting the kernel (entry_offset: 0x00751e00).
Linux version 6.14.0 (cnk2@ombertech) (gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40) #3 SMP Sun Apr  6 21:54:11 UTC 2025
BIOS-provided physical RAM map:
BIOS-e820: [mem 0x0000000000000000-0x0000000000004c1f] usable
BIOS-e820: [mem 0x0000000000004c20-0x000000000000501f] reserved
BIOS-e820: [mem 0x0000000000005020-0x000000000009ffff] usable
BIOS-e820: [mem 0x00000000000f5a3c-0x00000000000fffff] reserved
BIOS-e820: [mem 0x0000000000100000-0x00000000013fffff] usable
BIOS-e820: [mem 0x00000000ffff5a3c-0x00000000ffffffff] reserved
printk: legacy console [earlyser0] enabled
printk: debug: ignoring loglevel setting.
Notice: NX (Execute Disable) protection missing in CPU!
APIC: Static calls initialized
DMI not present or invalid.
e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
e820: remove [mem 0x000a0000-0x000fffff] usable
last_pfn = 0x1400 max_arch_pfn = 0x100000
MTRRs disabled (not available)
x86/PAT: PAT not supported by the CPU.
x86/PAT: Configuration [0-7]: WB  WT  UC- UC  WB  WT  UC- UC  
initial memory mapped: [mem 0x00000000-0x00ffffff]
0MB HIGHMEM available.
20MB LOWMEM available.
  mapped low ram: 0 - 01400000
  low ram: 0 - 01400000
Zone ranges:
  DMA      [mem 0x0000000000001000-0x0000000000ffffff]
  Normal   [mem 0x0000000001000000-0x00000000013fffff]
  HighMem  empty
Movable zone start for each node
Early memory node ranges
  node   0: [mem 0x0000000000001000-0x0000000000003fff]
  node   0: [mem 0x0000000000006000-0x000000000009ffff]
  node   0: [mem 0x0000000000100000-0x00000000013fffff]
Initmem setup node 0 [mem 0x0000000000001000-0x00000000013fffff]
On node 0, zone DMA: 1 pages in unavailable ranges
On node 0, zone DMA: 2 pages in unavailable ranges
On node 0, zone DMA: 96 pages in unavailable ranges
No local APIC present or hardware disabled
APIC: disable apic facility
APIC: Switched APIC routing to: noop
CPU topo: Max. logical packages:   1
CPU topo: Max. logical dies:       1
CPU topo: Max. dies per package:   1
CPU topo: Max. threads per core:   1
CPU topo: Num. cores per package:     1
CPU topo: Num. threads per package:   1
CPU topo: Allowing 1 present CPUs plus 0 hotplug CPUs
PM: hibernation: Registered nosave memory: [mem 0x00000000-0x00000fff]
PM: hibernation: Registered nosave memory: [mem 0x00004000-0x00004fff]
PM: hibernation: Registered nosave memory: [mem 0x00005000-0x00005fff]
PM: hibernation: Registered nosave memory: [mem 0x000a0000-0x000f5fff]
PM: hibernation: Registered nosave memory: [mem 0x000f6000-0x000fffff]
[mem 0x01400000-0xffff5a3b] available for PCI devices
Booting paravirtualized kernel on bare hardware
clocksource: refined-jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 6370452778343963 ns
setup_percpu: NR_CPUS:8 nr_cpumask_bits:1 nr_cpu_ids:1 nr_node_ids:1
percpu: Embedded 30 pages/cpu s91852 r0 d31028 u122880
pcpu-alloc: s91852 r0 d31028 u122880 alloc=30*4096
pcpu-alloc: [0] 0 
Kernel command line: root=/dev/sda3 rw base udev.children-max=1 acpi=off earlyprintk=ttyS0,115200,keep ignore_loglevel BOOT_IMAGE=614-4864
Unknown kernel command line parameters "base BOOT_IMAGE=614-4864", will be passed to user space.
printk: log buffer data + meta data: 131072 + 409600 = 540672 bytes
Dentry cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
Inode-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
Built 1 zonelists, mobility grouping on.  Total pages: 5021
mem auto-init: stack:off, heap alloc:off, heap free:off
Initializing HighMem for node 0 (00000000:00000000)
Checking if this processor honours the WP bit even in supervisor mode...Ok.
SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
rcu: Hierarchical RCU implementation.
rcu: 	RCU restricting CPUs from NR_CPUS=8 to nr_cpu_ids=1.
	Tracing variant of Tasks RCU enabled.
rcu: RCU calculated value of scheduler-enlistment delay is 30 jiffies.
rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=1
RCU Tasks Trace: Setting shift to 0 and lim to 1 rcu_task_cb_adjust=1 rcu_task_cpu_ids=1.
NR_IRQS: 2304, nr_irqs: 32, preallocated irqs: 16
rcu: srcu_init: Setting srcu_struct sizes based on contention.
Console: colour VGA+ 80x60
printk: legacy console [tty0] enabled
APIC: Keep in PIC mode(8259)
Calibrating delay loop... 30.96 BogoMIPS (lpj=51136)
Last level iTLB entries: 4KB 0, 2MB 0, 4MB 0
Last level dTLB entries: 4KB 0, 2MB 0, 4MB 0, 1GB 0
x86/fpu: Probing for FPU: FSW=0x0000 FCW=0x037f
x86/fpu: x87 FPU will use FSAVE
Freeing SMP alternatives memory: 24K
pid_max: default: 32768 minimum: 301
Mount-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
smpboot: SMP disabled
Performance Events: no PMU driver, software events only.
signal: max sigframe size: 928
Oops: invalid opcode: 0000 [#1] SMP
CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.14.0 #3
EIP: 0xc0b5e1da
Code: 7d dc 00 74 0b b9 07 00 00 00 89 df b0 01 f3 a5 83 c4 1c 5b 5e 5f 5d c3 55 b8 01 00 00 00 89 e5 57 56 31 f6 53 89 f1 83 ec 30 <0f> a2 b9 04 00 00 00 89 45 c4 8d 7d c8 89 f0 f3 ab e8 3c fb ff ff
EAX: 00000001 EBX: c0be6b00 ECX: 00000000 EDX: 00000246
ESI: 00000000 EDI: 00000000 EBP: c1309f08 ESP: c1309ecc
DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010286
CR0: 80050033 CR2: ffd38000 CR3: 00c16000 CR4: 00000000
Call Trace:
 ? 0xc01231af
 ? 0xc01231c8
 ? 0xc0123222
 ? 0xc0123245
 ? 0xc01215ef
 ? 0xc01217f7
 ? 0xc0b5e1da
 ? 0xc0848e09
 ? 0xc012186f
 ? 0xc0b5e1da
 ? 0xc0848e41
 ? 0xc010105d
 ? 0xc01500d8
 ? 0xc0848e09
 ? 0xc0b5e1da
 ? 0xc01500d8
 ? 0xc0848e09
 ? 0xc0b5e1da
 ? 0xc085148a
 ? 0xc0524da8
 ? 0xc0b5e1c8
 0xc0102100
 ? 0xc08514d5
 ? 0xc085148a
 ? 0xc0171bde
 ? 0xc0175987
 ? 0xc016d672
 0xc0b4c9e2
 ? 0xc084c9b8
 0xc084c9ca
 0xc0127d3a
 ? 0xc084c9b8
 0xc01027a2
 0xc0100e3d
Modules linked in:
---[ end trace 0000000000000000 ]---
EIP: 0xc0b5e1da
Code: 7d dc 00 74 0b b9 07 00 00 00 89 df b0 01 f3 a5 83 c4 1c 5b 5e 5f 5d c3 55 b8 01 00 00 00 89 e5 57 56 31 f6 53 89 f1 83 ec 30 <0f> a2 b9 04 00 00 00 89 45 c4 8d 7d c8 89 f0 f3 ab e8 3c fb ff ff
EAX: 00000001 EBX: c0be6b00 ECX: 00000000 EDX: 00000246
ESI: 00000000 EDI: 00000000 EBP: c1309f08 ESP: c1309ecc
DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010286
CR0: 80050033 CR2: ffd38000 CR3: 00c16000 CR4: 00000000
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
Rebooting in 60 seconds..