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x86/bugs: Restructure spectre_v2_user mitigation

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Restructure spectre_v2_user to use select/update/apply functions to
create consistent vulnerability handling.

The IBPB/STIBP choices are first decided based on the spectre_v2_user
command line but can be modified by the spectre_v2 command line option
as well.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/20250418161721.1855190-12-david.kaplan@amd.com
This commit is contained in:
David Kaplan
2025-04-18 11:17:16 -05:00
committed by Borislav Petkov (AMD)
parent e3b78a7ad5
commit ddfca9430a
1 changed files with 97 additions and 77 deletions
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174
arch/x86/kernel/cpu/bugs.c
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@@ -60,6 +60,8 @@ static void __init retbleed_select_mitigation(void);
static void __init retbleed_update_mitigation(void);
static void __init retbleed_apply_mitigation(void);
static void __init spectre_v2_user_select_mitigation(void);
static void __init spectre_v2_user_update_mitigation(void);
static void __init spectre_v2_user_apply_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);
static void __init mds_select_mitigation(void);
@@ -190,11 +192,6 @@ void __init cpu_select_mitigations(void)
spectre_v1_select_mitigation();
spectre_v2_select_mitigation();
retbleed_select_mitigation();
/*
* spectre_v2_user_select_mitigation() relies on the state set by
* retbleed_select_mitigation(); specifically the STIBP selection is
* forced for UNRET or IBPB.
*/
spectre_v2_user_select_mitigation();
ssb_select_mitigation();
l1tf_select_mitigation();
@@ -217,6 +214,13 @@ void __init cpu_select_mitigations(void)
* choices.
*/
retbleed_update_mitigation();
/*
* spectre_v2_user_update_mitigation() depends on
* retbleed_update_mitigation(), specifically the STIBP
* selection is forced for UNRET or IBPB.
*/
spectre_v2_user_update_mitigation();
mds_update_mitigation();
taa_update_mitigation();
mmio_update_mitigation();
@@ -224,6 +228,7 @@ void __init cpu_select_mitigations(void)
spectre_v1_apply_mitigation();
retbleed_apply_mitigation();
spectre_v2_user_apply_mitigation();
mds_apply_mitigation();
taa_apply_mitigation();
mmio_apply_mitigation();
@@ -1379,6 +1384,8 @@ enum spectre_v2_mitigation_cmd {
SPECTRE_V2_CMD_IBRS,
};
static enum spectre_v2_mitigation_cmd spectre_v2_cmd __ro_after_init = SPECTRE_V2_CMD_AUTO;
enum spectre_v2_user_cmd {
SPECTRE_V2_USER_CMD_NONE,
SPECTRE_V2_USER_CMD_AUTO,
@@ -1417,31 +1424,18 @@ static void __init spec_v2_user_print_cond(const char *reason, bool secure)
pr_info("spectre_v2_user=%s forced on command line.\n", reason);
}
static __ro_after_init enum spectre_v2_mitigation_cmd spectre_v2_cmd;
static enum spectre_v2_user_cmd __init
spectre_v2_parse_user_cmdline(void)
static enum spectre_v2_user_cmd __init spectre_v2_parse_user_cmdline(void)
{
enum spectre_v2_user_cmd mode;
char arg[20];
int ret, i;
mode = IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2) ?
SPECTRE_V2_USER_CMD_AUTO : SPECTRE_V2_USER_CMD_NONE;
switch (spectre_v2_cmd) {
case SPECTRE_V2_CMD_NONE:
if (cpu_mitigations_off() || !IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2))
return SPECTRE_V2_USER_CMD_NONE;
case SPECTRE_V2_CMD_FORCE:
return SPECTRE_V2_USER_CMD_FORCE;
default:
break;
}
ret = cmdline_find_option(boot_command_line, "spectre_v2_user",
arg, sizeof(arg));
if (ret < 0)
return mode;
return SPECTRE_V2_USER_CMD_AUTO;
for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) {
if (match_option(arg, ret, v2_user_options[i].option)) {
@@ -1452,7 +1446,7 @@ spectre_v2_parse_user_cmdline(void)
}
pr_err("Unknown user space protection option (%s). Switching to default\n", arg);
return mode;
return SPECTRE_V2_USER_CMD_AUTO;
}
static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)
@@ -1460,60 +1454,72 @@ static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)
return spectre_v2_in_eibrs_mode(mode) || mode == SPECTRE_V2_IBRS;
}
static void __init
spectre_v2_user_select_mitigation(void)
static void __init spectre_v2_user_select_mitigation(void)
{
enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE;
enum spectre_v2_user_cmd cmd;
if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
return;
cmd = spectre_v2_parse_user_cmdline();
switch (cmd) {
switch (spectre_v2_parse_user_cmdline()) {
case SPECTRE_V2_USER_CMD_NONE:
goto set_mode;
return;
case SPECTRE_V2_USER_CMD_FORCE:
mode = SPECTRE_V2_USER_STRICT;
spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT;
spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT;
break;
case SPECTRE_V2_USER_CMD_AUTO:
case SPECTRE_V2_USER_CMD_PRCTL:
spectre_v2_user_ibpb = SPECTRE_V2_USER_PRCTL;
spectre_v2_user_stibp = SPECTRE_V2_USER_PRCTL;
break;
case SPECTRE_V2_USER_CMD_PRCTL_IBPB:
mode = SPECTRE_V2_USER_PRCTL;
spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT;
spectre_v2_user_stibp = SPECTRE_V2_USER_PRCTL;
break;
case SPECTRE_V2_USER_CMD_SECCOMP:
case SPECTRE_V2_USER_CMD_SECCOMP_IBPB:
if (IS_ENABLED(CONFIG_SECCOMP))
mode = SPECTRE_V2_USER_SECCOMP;
spectre_v2_user_ibpb = SPECTRE_V2_USER_SECCOMP;
else
mode = SPECTRE_V2_USER_PRCTL;
spectre_v2_user_ibpb = SPECTRE_V2_USER_PRCTL;
spectre_v2_user_stibp = spectre_v2_user_ibpb;
break;
case SPECTRE_V2_USER_CMD_SECCOMP_IBPB:
spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT;
if (IS_ENABLED(CONFIG_SECCOMP))
spectre_v2_user_stibp = SPECTRE_V2_USER_SECCOMP;
else
spectre_v2_user_stibp = SPECTRE_V2_USER_PRCTL;
break;
}
/* Initialize Indirect Branch Prediction Barrier */
if (boot_cpu_has(X86_FEATURE_IBPB)) {
static_branch_enable(&switch_vcpu_ibpb);
/*
* At this point, an STIBP mode other than "off" has been set.
* If STIBP support is not being forced, check if STIBP always-on
* is preferred.
*/
if ((spectre_v2_user_stibp == SPECTRE_V2_USER_PRCTL ||
spectre_v2_user_stibp == SPECTRE_V2_USER_SECCOMP) &&
boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT_PREFERRED;
spectre_v2_user_ibpb = mode;
switch (cmd) {
case SPECTRE_V2_USER_CMD_NONE:
break;
case SPECTRE_V2_USER_CMD_FORCE:
case SPECTRE_V2_USER_CMD_PRCTL_IBPB:
case SPECTRE_V2_USER_CMD_SECCOMP_IBPB:
static_branch_enable(&switch_mm_always_ibpb);
spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT;
break;
case SPECTRE_V2_USER_CMD_PRCTL:
case SPECTRE_V2_USER_CMD_AUTO:
case SPECTRE_V2_USER_CMD_SECCOMP:
static_branch_enable(&switch_mm_cond_ibpb);
break;
}
if (!boot_cpu_has(X86_FEATURE_IBPB))
spectre_v2_user_ibpb = SPECTRE_V2_USER_NONE;
pr_info("mitigation: Enabling %s Indirect Branch Prediction Barrier\n",
static_key_enabled(&switch_mm_always_ibpb) ?
"always-on" : "conditional");
if (!boot_cpu_has(X86_FEATURE_STIBP))
spectre_v2_user_stibp = SPECTRE_V2_USER_NONE;
}
static void __init spectre_v2_user_update_mitigation(void)
{
if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
return;
/* The spectre_v2 cmd line can override spectre_v2_user options */
if (spectre_v2_cmd == SPECTRE_V2_CMD_NONE) {
spectre_v2_user_ibpb = SPECTRE_V2_USER_NONE;
spectre_v2_user_stibp = SPECTRE_V2_USER_NONE;
} else if (spectre_v2_cmd == SPECTRE_V2_CMD_FORCE) {
spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT;
spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT;
}
/*
@@ -1531,30 +1537,44 @@ spectre_v2_user_select_mitigation(void)
if (!boot_cpu_has(X86_FEATURE_STIBP) ||
!cpu_smt_possible() ||
(spectre_v2_in_eibrs_mode(spectre_v2_enabled) &&
!boot_cpu_has(X86_FEATURE_AUTOIBRS)))
!boot_cpu_has(X86_FEATURE_AUTOIBRS))) {
spectre_v2_user_stibp = SPECTRE_V2_USER_NONE;
return;
/*
* At this point, an STIBP mode other than "off" has been set.
* If STIBP support is not being forced, check if STIBP always-on
* is preferred.
*/
if (mode != SPECTRE_V2_USER_STRICT &&
boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
mode = SPECTRE_V2_USER_STRICT_PREFERRED;
if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET ||
retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
if (mode != SPECTRE_V2_USER_STRICT &&
mode != SPECTRE_V2_USER_STRICT_PREFERRED)
pr_info("Selecting STIBP always-on mode to complement retbleed mitigation\n");
mode = SPECTRE_V2_USER_STRICT_PREFERRED;
}
spectre_v2_user_stibp = mode;
if (spectre_v2_user_stibp != SPECTRE_V2_USER_NONE &&
(retbleed_mitigation == RETBLEED_MITIGATION_UNRET ||
retbleed_mitigation == RETBLEED_MITIGATION_IBPB)) {
if (spectre_v2_user_stibp != SPECTRE_V2_USER_STRICT &&
spectre_v2_user_stibp != SPECTRE_V2_USER_STRICT_PREFERRED)
pr_info("Selecting STIBP always-on mode to complement retbleed mitigation\n");
spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT_PREFERRED;
}
pr_info("%s\n", spectre_v2_user_strings[spectre_v2_user_stibp]);
}
set_mode:
pr_info("%s\n", spectre_v2_user_strings[mode]);
static void __init spectre_v2_user_apply_mitigation(void)
{
/* Initialize Indirect Branch Prediction Barrier */
if (spectre_v2_user_ibpb != SPECTRE_V2_USER_NONE) {
static_branch_enable(&switch_vcpu_ibpb);
switch (spectre_v2_user_ibpb) {
case SPECTRE_V2_USER_STRICT:
static_branch_enable(&switch_mm_always_ibpb);
break;
case SPECTRE_V2_USER_PRCTL:
case SPECTRE_V2_USER_SECCOMP:
static_branch_enable(&switch_mm_cond_ibpb);
break;
default:
break;
}
pr_info("mitigation: Enabling %s Indirect Branch Prediction Barrier\n",
static_key_enabled(&switch_mm_always_ibpb) ?
"always-on" : "conditional");
}
}
static const char * const spectre_v2_strings[] = {