2 * Copyright (C) 1994 Linus Torvalds
4 * Cyrix stuff, June 1998 by:
5 * - Rafael R. Reilova (moved everything from head.S),
6 * <rreilova@ececs.uc.edu>
7 * - Channing Corn (tests & fixes),
8 * - Andrew D. Balsa (code cleanup).
10 #include <linux/init.h>
11 #include <linux/utsname.h>
12 #include <linux/cpu.h>
13 #include <linux/smp.h>
14 #include <linux/nospec.h>
15 #include <linux/prctl.h>
17 #include <asm/spec-ctrl.h>
18 #include <asm/cmdline.h>
20 #include <asm/processor.h>
21 #include <asm/processor-flags.h>
22 #include <asm/fpu/internal.h>
24 #include <asm/paravirt.h>
25 #include <asm/alternative.h>
26 #include <asm/pgtable.h>
27 #include <asm/set_memory.h>
28 #include <asm/intel-family.h>
30 static void __init
spectre_v2_select_mitigation(void);
31 static void __init
ssb_select_mitigation(void);
34 * Our boot-time value of the SPEC_CTRL MSR. We read it once so that any
35 * writes to SPEC_CTRL contain whatever reserved bits have been set.
37 u64 __ro_after_init x86_spec_ctrl_base
;
38 EXPORT_SYMBOL_GPL(x86_spec_ctrl_base
);
41 * The vendor and possibly platform specific bits which can be modified in
44 static u64 __ro_after_init x86_spec_ctrl_mask
= SPEC_CTRL_IBRS
;
47 * AMD specific MSR info for Speculative Store Bypass control.
48 * x86_amd_ls_cfg_ssbd_mask is initialized in identify_boot_cpu().
50 u64 __ro_after_init x86_amd_ls_cfg_base
;
51 u64 __ro_after_init x86_amd_ls_cfg_ssbd_mask
;
53 void __init
check_bugs(void)
57 if (!IS_ENABLED(CONFIG_SMP
)) {
59 print_cpu_info(&boot_cpu_data
);
63 * Read the SPEC_CTRL MSR to account for reserved bits which may
64 * have unknown values. AMD64_LS_CFG MSR is cached in the early AMD
65 * init code as it is not enumerated and depends on the family.
67 if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL
))
68 rdmsrl(MSR_IA32_SPEC_CTRL
, x86_spec_ctrl_base
);
70 /* Select the proper spectre mitigation before patching alternatives */
71 spectre_v2_select_mitigation();
74 * Select proper mitigation for any exposure to the Speculative Store
75 * Bypass vulnerability.
77 ssb_select_mitigation();
81 * Check whether we are able to run this kernel safely on SMP.
83 * - i386 is no longer supported.
84 * - In order to run on anything without a TSC, we need to be
85 * compiled for a i486.
87 if (boot_cpu_data
.x86
< 4)
88 panic("Kernel requires i486+ for 'invlpg' and other features");
90 init_utsname()->machine
[1] =
91 '0' + (boot_cpu_data
.x86
> 6 ? 6 : boot_cpu_data
.x86
);
92 alternative_instructions();
94 fpu__init_check_bugs();
95 #else /* CONFIG_X86_64 */
96 alternative_instructions();
99 * Make sure the first 2MB area is not mapped by huge pages
100 * There are typically fixed size MTRRs in there and overlapping
101 * MTRRs into large pages causes slow downs.
103 * Right now we don't do that with gbpages because there seems
104 * very little benefit for that case.
107 set_memory_4k((unsigned long)__va(0), 1);
111 /* The kernel command line selection */
112 enum spectre_v2_mitigation_cmd
{
115 SPECTRE_V2_CMD_FORCE
,
116 SPECTRE_V2_CMD_RETPOLINE
,
117 SPECTRE_V2_CMD_RETPOLINE_GENERIC
,
118 SPECTRE_V2_CMD_RETPOLINE_AMD
,
121 static const char *spectre_v2_strings
[] = {
122 [SPECTRE_V2_NONE
] = "Vulnerable",
123 [SPECTRE_V2_RETPOLINE_MINIMAL
] = "Vulnerable: Minimal generic ASM retpoline",
124 [SPECTRE_V2_RETPOLINE_MINIMAL_AMD
] = "Vulnerable: Minimal AMD ASM retpoline",
125 [SPECTRE_V2_RETPOLINE_GENERIC
] = "Mitigation: Full generic retpoline",
126 [SPECTRE_V2_RETPOLINE_AMD
] = "Mitigation: Full AMD retpoline",
130 #define pr_fmt(fmt) "Spectre V2 mitigation: " fmt
132 static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init
=
136 x86_virt_spec_ctrl(u64 guest_spec_ctrl
, u64 guest_virt_spec_ctrl
, bool setguest
)
138 u64 msrval
, guestval
, hostval
= x86_spec_ctrl_base
;
139 struct thread_info
*ti
= current_thread_info();
141 /* Is MSR_SPEC_CTRL implemented ? */
142 if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL
)) {
144 * Restrict guest_spec_ctrl to supported values. Clear the
145 * modifiable bits in the host base value and or the
146 * modifiable bits from the guest value.
148 guestval
= hostval
& ~x86_spec_ctrl_mask
;
149 guestval
|= guest_spec_ctrl
& x86_spec_ctrl_mask
;
151 /* SSBD controlled in MSR_SPEC_CTRL */
152 if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD
))
153 hostval
|= ssbd_tif_to_spec_ctrl(ti
->flags
);
155 if (hostval
!= guestval
) {
156 msrval
= setguest
? guestval
: hostval
;
157 wrmsrl(MSR_IA32_SPEC_CTRL
, msrval
);
161 EXPORT_SYMBOL_GPL(x86_virt_spec_ctrl
);
163 static void x86_amd_ssb_disable(void)
165 u64 msrval
= x86_amd_ls_cfg_base
| x86_amd_ls_cfg_ssbd_mask
;
167 if (boot_cpu_has(X86_FEATURE_VIRT_SSBD
))
168 wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL
, SPEC_CTRL_SSBD
);
169 else if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD
))
170 wrmsrl(MSR_AMD64_LS_CFG
, msrval
);
173 static void __init
spec2_print_if_insecure(const char *reason
)
175 if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2
))
176 pr_info("%s\n", reason
);
179 static void __init
spec2_print_if_secure(const char *reason
)
181 if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2
))
182 pr_info("%s\n", reason
);
185 static inline bool retp_compiler(void)
187 return __is_defined(RETPOLINE
);
190 static inline bool match_option(const char *arg
, int arglen
, const char *opt
)
192 int len
= strlen(opt
);
194 return len
== arglen
&& !strncmp(arg
, opt
, len
);
197 static enum spectre_v2_mitigation_cmd __init
spectre_v2_parse_cmdline(void)
202 ret
= cmdline_find_option(boot_command_line
, "spectre_v2", arg
,
205 if (match_option(arg
, ret
, "off")) {
207 } else if (match_option(arg
, ret
, "on")) {
208 spec2_print_if_secure("force enabled on command line.");
209 return SPECTRE_V2_CMD_FORCE
;
210 } else if (match_option(arg
, ret
, "retpoline")) {
211 spec2_print_if_insecure("retpoline selected on command line.");
212 return SPECTRE_V2_CMD_RETPOLINE
;
213 } else if (match_option(arg
, ret
, "retpoline,amd")) {
214 if (boot_cpu_data
.x86_vendor
!= X86_VENDOR_AMD
) {
215 pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
216 return SPECTRE_V2_CMD_AUTO
;
218 spec2_print_if_insecure("AMD retpoline selected on command line.");
219 return SPECTRE_V2_CMD_RETPOLINE_AMD
;
220 } else if (match_option(arg
, ret
, "retpoline,generic")) {
221 spec2_print_if_insecure("generic retpoline selected on command line.");
222 return SPECTRE_V2_CMD_RETPOLINE_GENERIC
;
223 } else if (match_option(arg
, ret
, "auto")) {
224 return SPECTRE_V2_CMD_AUTO
;
228 if (!cmdline_find_option_bool(boot_command_line
, "nospectre_v2"))
229 return SPECTRE_V2_CMD_AUTO
;
231 spec2_print_if_insecure("disabled on command line.");
232 return SPECTRE_V2_CMD_NONE
;
235 /* Check for Skylake-like CPUs (for RSB handling) */
236 static bool __init
is_skylake_era(void)
238 if (boot_cpu_data
.x86_vendor
== X86_VENDOR_INTEL
&&
239 boot_cpu_data
.x86
== 6) {
240 switch (boot_cpu_data
.x86_model
) {
241 case INTEL_FAM6_SKYLAKE_MOBILE
:
242 case INTEL_FAM6_SKYLAKE_DESKTOP
:
243 case INTEL_FAM6_SKYLAKE_X
:
244 case INTEL_FAM6_KABYLAKE_MOBILE
:
245 case INTEL_FAM6_KABYLAKE_DESKTOP
:
252 static void __init
spectre_v2_select_mitigation(void)
254 enum spectre_v2_mitigation_cmd cmd
= spectre_v2_parse_cmdline();
255 enum spectre_v2_mitigation mode
= SPECTRE_V2_NONE
;
258 * If the CPU is not affected and the command line mode is NONE or AUTO
259 * then nothing to do.
261 if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2
) &&
262 (cmd
== SPECTRE_V2_CMD_NONE
|| cmd
== SPECTRE_V2_CMD_AUTO
))
266 case SPECTRE_V2_CMD_NONE
:
269 case SPECTRE_V2_CMD_FORCE
:
271 case SPECTRE_V2_CMD_AUTO
:
274 case SPECTRE_V2_CMD_RETPOLINE_AMD
:
275 if (IS_ENABLED(CONFIG_RETPOLINE
))
278 case SPECTRE_V2_CMD_RETPOLINE_GENERIC
:
279 if (IS_ENABLED(CONFIG_RETPOLINE
))
280 goto retpoline_generic
;
282 case SPECTRE_V2_CMD_RETPOLINE
:
283 if (IS_ENABLED(CONFIG_RETPOLINE
))
287 pr_err("kernel not compiled with retpoline; no mitigation available!");
291 if (boot_cpu_data
.x86_vendor
== X86_VENDOR_AMD
) {
293 if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC
)) {
294 pr_err("LFENCE not serializing. Switching to generic retpoline\n");
295 goto retpoline_generic
;
297 mode
= retp_compiler() ? SPECTRE_V2_RETPOLINE_AMD
:
298 SPECTRE_V2_RETPOLINE_MINIMAL_AMD
;
299 setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD
);
300 setup_force_cpu_cap(X86_FEATURE_RETPOLINE
);
303 mode
= retp_compiler() ? SPECTRE_V2_RETPOLINE_GENERIC
:
304 SPECTRE_V2_RETPOLINE_MINIMAL
;
305 setup_force_cpu_cap(X86_FEATURE_RETPOLINE
);
308 spectre_v2_enabled
= mode
;
309 pr_info("%s\n", spectre_v2_strings
[mode
]);
311 pr_info("Speculation control IBPB %s IBRS %s",
312 ibpb_supported
? "supported" : "not-supported",
313 ibrs_supported
? "supported" : "not-supported");
316 * If we have a full retpoline mode and then disable IBPB in kernel mode
317 * we do not require both.
319 if (mode
== SPECTRE_V2_RETPOLINE_AMD
||
320 mode
== SPECTRE_V2_RETPOLINE_GENERIC
)
322 if (ibrs_supported
) {
323 pr_info("Retpoline compiled kernel. Defaulting IBRS to disabled");
326 sysctl_ibrs_enabled
= 0;
331 * If neither SMEP or KPTI are available, there is a risk of
332 * hitting userspace addresses in the RSB after a context switch
333 * from a shallow call stack to a deeper one. To prevent this fill
334 * the entire RSB, even when using IBRS.
336 * Skylake era CPUs have a separate issue with *underflow* of the
337 * RSB, when they will predict 'ret' targets from the generic BTB.
338 * The proper mitigation for this is IBRS. If IBRS is not supported
339 * or deactivated in favour of retpolines the RSB fill on context
340 * switch is required.
342 if ((!boot_cpu_has(X86_FEATURE_PTI
) &&
343 !boot_cpu_has(X86_FEATURE_SMEP
)) || is_skylake_era()) {
344 setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW
);
345 pr_info("Filling RSB on context switch\n");
350 #define pr_fmt(fmt) "Speculative Store Bypass: " fmt
352 static enum ssb_mitigation ssb_mode __ro_after_init
= SPEC_STORE_BYPASS_NONE
;
354 /* The kernel command line selection */
355 enum ssb_mitigation_cmd
{
356 SPEC_STORE_BYPASS_CMD_NONE
,
357 SPEC_STORE_BYPASS_CMD_AUTO
,
358 SPEC_STORE_BYPASS_CMD_ON
,
359 SPEC_STORE_BYPASS_CMD_PRCTL
,
360 SPEC_STORE_BYPASS_CMD_SECCOMP
,
363 static const char *ssb_strings
[] = {
364 [SPEC_STORE_BYPASS_NONE
] = "Vulnerable",
365 [SPEC_STORE_BYPASS_DISABLE
] = "Mitigation: Speculative Store Bypass disabled",
366 [SPEC_STORE_BYPASS_PRCTL
] = "Mitigation: Speculative Store Bypass disabled via prctl",
367 [SPEC_STORE_BYPASS_SECCOMP
] = "Mitigation: Speculative Store Bypass disabled via prctl and seccomp",
370 static const struct {
372 enum ssb_mitigation_cmd cmd
;
373 } ssb_mitigation_options
[] = {
374 { "auto", SPEC_STORE_BYPASS_CMD_AUTO
}, /* Platform decides */
375 { "on", SPEC_STORE_BYPASS_CMD_ON
}, /* Disable Speculative Store Bypass */
376 { "off", SPEC_STORE_BYPASS_CMD_NONE
}, /* Don't touch Speculative Store Bypass */
377 { "prctl", SPEC_STORE_BYPASS_CMD_PRCTL
}, /* Disable Speculative Store Bypass via prctl */
378 { "seccomp", SPEC_STORE_BYPASS_CMD_SECCOMP
}, /* Disable Speculative Store Bypass via prctl and seccomp */
381 static enum ssb_mitigation_cmd __init
ssb_parse_cmdline(void)
383 enum ssb_mitigation_cmd cmd
= SPEC_STORE_BYPASS_CMD_AUTO
;
387 if (cmdline_find_option_bool(boot_command_line
, "nospec_store_bypass_disable")) {
388 return SPEC_STORE_BYPASS_CMD_NONE
;
390 ret
= cmdline_find_option(boot_command_line
, "spec_store_bypass_disable",
393 return SPEC_STORE_BYPASS_CMD_AUTO
;
395 for (i
= 0; i
< ARRAY_SIZE(ssb_mitigation_options
); i
++) {
396 if (!match_option(arg
, ret
, ssb_mitigation_options
[i
].option
))
399 cmd
= ssb_mitigation_options
[i
].cmd
;
403 if (i
>= ARRAY_SIZE(ssb_mitigation_options
)) {
404 pr_err("unknown option (%s). Switching to AUTO select\n", arg
);
405 return SPEC_STORE_BYPASS_CMD_AUTO
;
412 static enum ssb_mitigation __init
__ssb_select_mitigation(void)
414 enum ssb_mitigation mode
= SPEC_STORE_BYPASS_NONE
;
415 enum ssb_mitigation_cmd cmd
;
417 if (!boot_cpu_has(X86_FEATURE_SSBD
))
420 cmd
= ssb_parse_cmdline();
421 if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS
) &&
422 (cmd
== SPEC_STORE_BYPASS_CMD_NONE
||
423 cmd
== SPEC_STORE_BYPASS_CMD_AUTO
))
427 case SPEC_STORE_BYPASS_CMD_AUTO
:
428 case SPEC_STORE_BYPASS_CMD_SECCOMP
:
430 * Choose prctl+seccomp as the default mode if seccomp is
433 if (IS_ENABLED(CONFIG_SECCOMP
))
434 mode
= SPEC_STORE_BYPASS_SECCOMP
;
436 mode
= SPEC_STORE_BYPASS_PRCTL
;
438 case SPEC_STORE_BYPASS_CMD_ON
:
439 mode
= SPEC_STORE_BYPASS_DISABLE
;
441 case SPEC_STORE_BYPASS_CMD_PRCTL
:
442 mode
= SPEC_STORE_BYPASS_PRCTL
;
444 case SPEC_STORE_BYPASS_CMD_NONE
:
449 * We have three CPU feature flags that are in play here:
450 * - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible.
451 * - X86_FEATURE_SSBD - CPU is able to turn off speculative store bypass
452 * - X86_FEATURE_SPEC_STORE_BYPASS_DISABLE - engage the mitigation
454 if (mode
== SPEC_STORE_BYPASS_DISABLE
) {
455 setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE
);
457 * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD uses
458 * a completely different MSR and bit dependent on family.
460 switch (boot_cpu_data
.x86_vendor
) {
461 case X86_VENDOR_INTEL
:
462 x86_spec_ctrl_base
|= SPEC_CTRL_SSBD
;
463 x86_spec_ctrl_mask
|= SPEC_CTRL_SSBD
;
464 wrmsrl(MSR_IA32_SPEC_CTRL
, x86_spec_ctrl_base
);
467 x86_amd_ssb_disable();
475 static void ssb_select_mitigation(void)
477 ssb_mode
= __ssb_select_mitigation();
479 if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS
))
480 pr_info("%s\n", ssb_strings
[ssb_mode
]);
484 #define pr_fmt(fmt) "Speculation prctl: " fmt
486 static int ssb_prctl_set(struct task_struct
*task
, unsigned long ctrl
)
490 if (ssb_mode
!= SPEC_STORE_BYPASS_PRCTL
&&
491 ssb_mode
!= SPEC_STORE_BYPASS_SECCOMP
)
496 /* If speculation is force disabled, enable is not allowed */
497 if (task_spec_ssb_force_disable(task
))
499 task_clear_spec_ssb_disable(task
);
500 update
= test_and_clear_tsk_thread_flag(task
, TIF_SSBD
);
502 case PR_SPEC_DISABLE
:
503 task_set_spec_ssb_disable(task
);
504 update
= !test_and_set_tsk_thread_flag(task
, TIF_SSBD
);
506 case PR_SPEC_FORCE_DISABLE
:
507 task_set_spec_ssb_disable(task
);
508 task_set_spec_ssb_force_disable(task
);
509 update
= !test_and_set_tsk_thread_flag(task
, TIF_SSBD
);
516 * If being set on non-current task, delay setting the CPU
517 * mitigation until it is next scheduled.
519 if (task
== current
&& update
)
520 speculative_store_bypass_update_current();
525 int arch_prctl_spec_ctrl_set(struct task_struct
*task
, unsigned long which
,
529 case PR_SPEC_STORE_BYPASS
:
530 return ssb_prctl_set(task
, ctrl
);
536 #ifdef CONFIG_SECCOMP
537 void arch_seccomp_spec_mitigate(struct task_struct
*task
)
539 if (ssb_mode
== SPEC_STORE_BYPASS_SECCOMP
)
540 ssb_prctl_set(task
, PR_SPEC_FORCE_DISABLE
);
544 static int ssb_prctl_get(struct task_struct
*task
)
547 case SPEC_STORE_BYPASS_DISABLE
:
548 return PR_SPEC_DISABLE
;
549 case SPEC_STORE_BYPASS_SECCOMP
:
550 case SPEC_STORE_BYPASS_PRCTL
:
551 if (task_spec_ssb_force_disable(task
))
552 return PR_SPEC_PRCTL
| PR_SPEC_FORCE_DISABLE
;
553 if (task_spec_ssb_disable(task
))
554 return PR_SPEC_PRCTL
| PR_SPEC_DISABLE
;
555 return PR_SPEC_PRCTL
| PR_SPEC_ENABLE
;
557 if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS
))
558 return PR_SPEC_ENABLE
;
559 return PR_SPEC_NOT_AFFECTED
;
563 int arch_prctl_spec_ctrl_get(struct task_struct
*task
, unsigned long which
)
566 case PR_SPEC_STORE_BYPASS
:
567 return ssb_prctl_get(task
);
573 void x86_spec_ctrl_setup_ap(void)
575 if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL
))
576 wrmsrl(MSR_IA32_SPEC_CTRL
, x86_spec_ctrl_base
);
578 if (ssb_mode
== SPEC_STORE_BYPASS_DISABLE
)
579 x86_amd_ssb_disable();
583 static ssize_t
cpu_show_common(struct device
*dev
, struct device_attribute
*attr
,
584 char *buf
, unsigned int bug
)
586 if (!boot_cpu_has_bug(bug
))
587 return sprintf(buf
, "Not affected\n");
590 case X86_BUG_CPU_MELTDOWN
:
591 if (boot_cpu_has(X86_FEATURE_PTI
))
592 return sprintf(buf
, "Mitigation: PTI\n");
595 case X86_BUG_SPECTRE_V1
:
597 return sprintf(buf
, "Mitigation: OSB (observable speculation barrier, Intel v6)\n");
599 case X86_BUG_SPECTRE_V2
:
600 return sprintf(buf
, "%s%s\n", spectre_v2_strings
[spectre_v2_enabled
], ibpb_inuse
? ", IBPB (Intel v4)" : "");
602 case X86_BUG_SPEC_STORE_BYPASS
:
603 return sprintf(buf
, "%s\n", ssb_strings
[ssb_mode
]);
609 return sprintf(buf
, "Vulnerable\n");
612 ssize_t
cpu_show_meltdown(struct device
*dev
, struct device_attribute
*attr
,
615 return cpu_show_common(dev
, attr
, buf
, X86_BUG_CPU_MELTDOWN
);
618 ssize_t
cpu_show_spectre_v1(struct device
*dev
, struct device_attribute
*attr
,
621 return cpu_show_common(dev
, attr
, buf
, X86_BUG_SPECTRE_V1
);
624 ssize_t
cpu_show_spectre_v2(struct device
*dev
, struct device_attribute
*attr
,
627 return cpu_show_common(dev
, attr
, buf
, X86_BUG_SPECTRE_V2
);
630 ssize_t
cpu_show_spec_store_bypass(struct device
*dev
, struct device_attribute
*attr
, char *buf
)
632 return cpu_show_common(dev
, attr
, buf
, X86_BUG_SPEC_STORE_BYPASS
);