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linux-stable-mirror/include/linux/cpu.h
Dave Hansen 4e2c719782 x86/cpu: Help users notice when running old Intel microcode 
Old microcode is bad for users and for kernel developers.

For users, it exposes them to known fixed security and/or functional
issues. These obviously rarely result in instant dumpster fires in
every environment. But it is as important to keep your microcode up
to date as it is to keep your kernel up to date.

Old microcode also makes kernels harder to debug. A developer looking
at an oops need to consider kernel bugs, known CPU issues and unknown
CPU issues as possible causes. If they know the microcode is up to
date, they can mostly eliminate known CPU issues as the cause.

Make it easier to tell if CPU microcode is out of date. Add a list
of released microcode. If the loaded microcode is older than the
release, tell users in a place that folks can find it:

	/sys/devices/system/cpu/vulnerabilities/old_microcode

Tell kernel kernel developers about it with the existing taint
flag:

	TAINT_CPU_OUT_OF_SPEC

== Discussion ==

When a user reports a potential kernel issue, it is very common
to ask them to reproduce the issue on mainline. Running mainline,
they will (independently from the distro) acquire a more up-to-date
microcode version list. If their microcode is old, they will
get a warning about the taint and kernel developers can take that
into consideration when debugging.

Just like any other entry in "vulnerabilities/", users are free to
make their own assessment of their exposure.

== Microcode Revision Discussion ==

The microcode versions in the table were generated from the Intel
microcode git repo:

	8ac9378a8487 ("microcode-20241112 Release")

which as of this writing lags behind the latest microcode-20250211.

It can be argued that the versions that the kernel picks to call "old"
should be a revision or two old. Which specific version is picked is
less important to me than picking *a* version and enforcing it.

This repository contains only microcode versions that Intel has deemed
to be OS-loadable. It is quite possible that the BIOS has loaded a
newer microcode than the latest in this repo. If this happens, the
system is considered to have new microcode, not old.

Specifically, the sysfs file and taint flag answer the question:

	Is the CPU running on the latest OS-loadable microcode,
	or something even later that the BIOS loaded?

In other words, Intel never publishes an authoritative list of CPUs
and latest microcode revisions. Until it does, this is the best that
Linux can do.

Also note that the "intel-ucode-defs.h" file is simple, ugly and
has lots of magic numbers. That's on purpose and should allow a
single file to be shared across lots of stable kernel regardless of if
they have the new "VFM" infrastructure or not. It was generated with
a dumb script.

== FAQ ==

Q: Does this tell me if my system is secure or insecure?
A: No. It only tells you if your microcode was old when the
   system booted.

Q: Should the kernel warn if the microcode list itself is too old?
A: No. New kernels will get new microcode lists, both mainline
   and stable. The only way to have an old list is to be running
   an old kernel in which case you have bigger problems.

Q: Is this for security or functional issues?
A: Both.

Q: If a given microcode update only has functional problems but
   no security issues, will it be considered old?
A: Yes. All microcode image versions within a microcode release
   are treated identically. Intel appears to make security
   updates without disclosing them in the release notes.  Thus,
   all updates are considered to be security-relevant.

Q: Who runs old microcode?
A: Anybody with an old distro. This happens all the time inside
   of Intel where there are lots of weird systems in labs that
   might not be getting regular distro updates and might also
   be running rather exotic microcode images.

Q: If I update my microcode after booting will it stop saying
   "Vulnerable"?
A: No. Just like all the other vulnerabilies, you need to
   reboot before the kernel will reassess your vulnerability.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: "Ahmed S. Darwish" <darwi@linutronix.de>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/all/20250421195659.CF426C07%40davehans-spike.ostc.intel.com
(cherry picked from commit 9127865b15eb0a1bd05ad7efe29489c44394bdc1)
2025-04-22 08:33:52 +02:00

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/* SPDX-License-Identifier: GPL-2.0 */
/*
* include/linux/cpu.h - generic cpu definition
*
* This is mainly for topological representation. We define the
* basic 'struct cpu' here, which can be embedded in per-arch
* definitions of processors.
*
* Basic handling of the devices is done in drivers/base/cpu.c
*
* CPUs are exported via sysfs in the devices/system/cpu
* directory.
*/
#ifndef _LINUX_CPU_H_
#define _LINUX_CPU_H_
#include <linux/node.h>
#include <linux/compiler.h>
#include <linux/cpuhotplug.h>
#include <linux/cpuhplock.h>
#include <linux/cpu_smt.h>
struct device;
struct device_node;
struct attribute_group;
struct cpu {
int node_id; /* The node which contains the CPU */
int hotpluggable; /* creates sysfs control file if hotpluggable */
struct device dev;
};
extern void boot_cpu_init(void);
extern void boot_cpu_hotplug_init(void);
extern void cpu_init(void);
extern void trap_init(void);
extern int register_cpu(struct cpu *cpu, int num);
extern struct device *get_cpu_device(unsigned cpu);
extern bool cpu_is_hotpluggable(unsigned cpu);
extern bool arch_match_cpu_phys_id(int cpu, u64 phys_id);
extern bool arch_find_n_match_cpu_physical_id(struct device_node *cpun,
int cpu, unsigned int *thread);
extern int cpu_add_dev_attr(struct device_attribute *attr);
extern void cpu_remove_dev_attr(struct device_attribute *attr);
extern int cpu_add_dev_attr_group(struct attribute_group *attrs);
extern void cpu_remove_dev_attr_group(struct attribute_group *attrs);
extern ssize_t cpu_show_meltdown(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_spectre_v1(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_spectre_v2(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_spec_store_bypass(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_l1tf(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_mds(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_tsx_async_abort(struct device *dev,
struct device_attribute *attr,
char *buf);
extern ssize_t cpu_show_itlb_multihit(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_srbds(struct device *dev, struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_mmio_stale_data(struct device *dev,
struct device_attribute *attr,
char *buf);
extern ssize_t cpu_show_retbleed(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_spec_rstack_overflow(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_gds(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_reg_file_data_sampling(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_ghostwrite(struct device *dev, struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_old_microcode(struct device *dev,
struct device_attribute *attr, char *buf);
extern __printf(4, 5)
struct device *cpu_device_create(struct device *parent, void *drvdata,
const struct attribute_group **groups,
const char *fmt, ...);
extern bool arch_cpu_is_hotpluggable(int cpu);
extern int arch_register_cpu(int cpu);
extern void arch_unregister_cpu(int cpu);
#ifdef CONFIG_HOTPLUG_CPU
extern void unregister_cpu(struct cpu *cpu);
extern ssize_t arch_cpu_probe(const char *, size_t);
extern ssize_t arch_cpu_release(const char *, size_t);
#endif
#ifdef CONFIG_GENERIC_CPU_DEVICES
DECLARE_PER_CPU(struct cpu, cpu_devices);
#endif
/*
* These states are not related to the core CPU hotplug mechanism. They are
* used by various (sub)architectures to track internal state
*/
#define CPU_ONLINE 0x0002 /* CPU is up */
#define CPU_UP_PREPARE 0x0003 /* CPU coming up */
#define CPU_DEAD 0x0007 /* CPU dead */
#define CPU_DEAD_FROZEN 0x0008 /* CPU timed out on unplug */
#define CPU_POST_DEAD 0x0009 /* CPU successfully unplugged */
#define CPU_BROKEN 0x000B /* CPU did not die properly */
#ifdef CONFIG_SMP
extern bool cpuhp_tasks_frozen;
int add_cpu(unsigned int cpu);
int cpu_device_up(struct device *dev);
void notify_cpu_starting(unsigned int cpu);
extern void cpu_maps_update_begin(void);
extern void cpu_maps_update_done(void);
int bringup_hibernate_cpu(unsigned int sleep_cpu);
void bringup_nonboot_cpus(unsigned int max_cpus);
#else /* CONFIG_SMP */
#define cpuhp_tasks_frozen 0
static inline void cpu_maps_update_begin(void)
{
}
static inline void cpu_maps_update_done(void)
{
}
static inline int add_cpu(unsigned int cpu) { return 0;}
#endif /* CONFIG_SMP */
extern const struct bus_type cpu_subsys;
#ifdef CONFIG_PM_SLEEP_SMP
extern int freeze_secondary_cpus(int primary);
extern void thaw_secondary_cpus(void);
static inline int suspend_disable_secondary_cpus(void)
{
int cpu = 0;
if (IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU))
cpu = -1;
return freeze_secondary_cpus(cpu);
}
static inline void suspend_enable_secondary_cpus(void)
{
thaw_secondary_cpus();
}
#else /* !CONFIG_PM_SLEEP_SMP */
static inline void thaw_secondary_cpus(void) {}
static inline int suspend_disable_secondary_cpus(void) { return 0; }
static inline void suspend_enable_secondary_cpus(void) { }
#endif /* !CONFIG_PM_SLEEP_SMP */
void __noreturn cpu_startup_entry(enum cpuhp_state state);
void cpu_idle_poll_ctrl(bool enable);
bool cpu_in_idle(unsigned long pc);
void arch_cpu_idle(void);
void arch_cpu_idle_prepare(void);
void arch_cpu_idle_enter(void);
void arch_cpu_idle_exit(void);
void arch_tick_broadcast_enter(void);
void arch_tick_broadcast_exit(void);
void __noreturn arch_cpu_idle_dead(void);
#ifdef CONFIG_ARCH_HAS_CPU_FINALIZE_INIT
void arch_cpu_finalize_init(void);
#else
static inline void arch_cpu_finalize_init(void) { }
#endif
void play_idle_precise(u64 duration_ns, u64 latency_ns);
static inline void play_idle(unsigned long duration_us)
{
play_idle_precise(duration_us * NSEC_PER_USEC, U64_MAX);
}
#ifdef CONFIG_HOTPLUG_CPU
void cpuhp_report_idle_dead(void);
#else
static inline void cpuhp_report_idle_dead(void) { }
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
#ifdef CONFIG_CPU_MITIGATIONS
extern bool cpu_mitigations_off(void);
extern bool cpu_mitigations_auto_nosmt(void);
#else
static inline bool cpu_mitigations_off(void)
{
return true;
}
static inline bool cpu_mitigations_auto_nosmt(void)
{
return false;
}
#endif
#endif /* _LINUX_CPU_H_ */
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