[RFC PATCH 12/34] x86/bugs: Restructure spectre_v2_user mitigation
From: David Kaplan
Date: Thu Sep 12 2024 - 15:11:27 EST
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@xxxxxxx>
---
arch/x86/kernel/cpu/bugs.c | 143 ++++++++++++++++++++-----------------
1 file changed, 79 insertions(+), 64 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 13143854ca42..eaef5a1cb4a3 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -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);
@@ -183,11 +185,6 @@ 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();
@@ -210,6 +207,7 @@ void __init cpu_select_mitigations(void)
* choices.
*/
retbleed_update_mitigation();
+ spectre_v2_user_update_mitigation();
mds_update_mitigation();
taa_update_mitigation();
mmio_update_mitigation();
@@ -217,6 +215,7 @@ 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();
@@ -1311,6 +1310,8 @@ enum spectre_v2_mitigation_cmd {
SPECTRE_V2_CMD_IBRS,
};
+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,
@@ -1349,22 +1350,14 @@ 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)
{
char arg[20];
int ret, i;
- switch (spectre_v2_cmd) {
- case SPECTRE_V2_CMD_NONE:
+ if (cpu_mitigations_off())
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));
@@ -1388,65 +1381,70 @@ 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)
{
- enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE;
- bool smt_possible = IS_ENABLED(CONFIG_SMP);
enum spectre_v2_user_cmd cmd;
if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
return;
- if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
- cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
- smt_possible = false;
-
cmd = spectre_v2_parse_user_cmdline();
switch (cmd) {
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;
+ spectre_v2_user_stibp = SPECTRE_V2_USER_PRCTL;
break;
}
- /* Initialize Indirect Branch Prediction Barrier */
- if (boot_cpu_has(X86_FEATURE_IBPB)) {
- setup_force_cpu_cap(X86_FEATURE_USE_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_STRICT &&
+ 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;
- }
+static void __init spectre_v2_user_update_mitigation(void)
+{
+ bool smt_possible = IS_ENABLED(CONFIG_SMP);
- pr_info("mitigation: Enabling %s Indirect Branch Prediction Barrier\n",
- static_key_enabled(&switch_mm_always_ibpb) ?
- "always-on" : "conditional");
+ if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
+ cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
+ smt_possible = false;
+
+ /* 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;
}
/*
@@ -1464,30 +1462,47 @@ spectre_v2_user_select_mitigation(void)
if (!boot_cpu_has(X86_FEATURE_STIBP) ||
!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)
+ if (spectre_v2_user_stibp != SPECTRE_V2_USER_NONE &&
+ 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");
- mode = SPECTRE_V2_USER_STRICT_PREFERRED;
+ spectre_v2_user_stibp = SPECTRE_V2_USER_STRICT_PREFERRED;
}
+ pr_info("%s\n", spectre_v2_user_strings[spectre_v2_user_stibp]);
+}
- spectre_v2_user_stibp = mode;
+static void __init spectre_v2_user_apply_mitigation(void)
+{
+ /* Initialize Indirect Branch Prediction Barrier */
+ if (boot_cpu_has(X86_FEATURE_IBPB) &&
+ spectre_v2_user_ibpb != SPECTRE_V2_USER_NONE) {
+ setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
-set_mode:
- pr_info("%s\n", spectre_v2_user_strings[mode]);
+ switch (spectre_v2_user_ibpb) {
+ case SPECTRE_V2_USER_NONE:
+ break;
+ 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[] = {
--
2.34.1