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Message-ID: <20250102145552.GQZ3ao-JFcCsRVWKfb@fat_crate.local>
Date: Thu, 2 Jan 2025 15:55:52 +0100
From: Borislav Petkov <bp@...en8.de>
To: David Kaplan <david.kaplan@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 18/35] x86/bugs: Restructure srso mitigation
On Tue, Nov 05, 2024 at 03:54:38PM -0600, David Kaplan wrote:
> @@ -2747,94 +2740,97 @@ static void __init srso_select_mitigation(void)
> setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
> return;
> }
> -
> - if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
> - srso_mitigation = SRSO_MITIGATION_IBPB;
> - goto out;
> - }
> } else {
> pr_warn("IBPB-extending microcode not applied!\n");
> pr_warn(SRSO_NOTICE);
>
> - /* may be overwritten by SRSO_CMD_SAFE_RET below */
> - srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED;
> + /* Fall-back to Safe-RET */
> + srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
> }
>
> - switch (srso_cmd) {
> - case SRSO_CMD_MICROCODE:
> - if (has_microcode) {
> - srso_mitigation = SRSO_MITIGATION_MICROCODE;
> - pr_warn(SRSO_NOTICE);
> - }
> + switch (srso_mitigation) {
> + case SRSO_MITIGATION_MICROCODE:
> + pr_warn(SRSO_NOTICE);
We're already dumping this message above in the else-branch of
(has_microcode).
Btw, here's a refreshed diff to accomodate the SRSO updates I did recently.
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 396d7c75fc2d..39ea02983b9e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -84,6 +84,8 @@ static void __init srbds_select_mitigation(void);
static void __init srbds_apply_mitigation(void);
static void __init l1d_flush_select_mitigation(void);
static void __init srso_select_mitigation(void);
+static void __init srso_update_mitigation(void);
+static void __init srso_apply_mitigation(void);
static void __init gds_select_mitigation(void);
static void __init gds_apply_mitigation(void);
static void __init bhi_select_mitigation(void);
@@ -200,11 +202,6 @@ void __init cpu_select_mitigations(void)
rfds_select_mitigation();
srbds_select_mitigation();
l1d_flush_select_mitigation();
-
- /*
- * srso_select_mitigation() depends and must run after
- * retbleed_select_mitigation().
- */
srso_select_mitigation();
gds_select_mitigation();
bhi_select_mitigation();
@@ -220,6 +217,7 @@ void __init cpu_select_mitigations(void)
taa_update_mitigation();
mmio_update_mitigation();
rfds_update_mitigation();
+ srso_update_mitigation();
spectre_v1_apply_mitigation();
spectre_v2_apply_mitigation();
@@ -232,6 +230,7 @@ void __init cpu_select_mitigations(void)
mmio_apply_mitigation();
rfds_apply_mitigation();
srbds_apply_mitigation();
+ srso_apply_mitigation();
gds_apply_mitigation();
bhi_apply_mitigation();
}
@@ -2658,6 +2657,7 @@ early_param("l1tf", l1tf_cmdline);
enum srso_mitigation {
SRSO_MITIGATION_NONE,
+ SRSO_MITIGATION_AUTO,
SRSO_MITIGATION_UCODE_NEEDED,
SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
SRSO_MITIGATION_MICROCODE,
@@ -2666,14 +2666,6 @@ enum srso_mitigation {
SRSO_MITIGATION_IBPB_ON_VMEXIT,
};
-enum srso_mitigation_cmd {
- SRSO_CMD_OFF,
- SRSO_CMD_MICROCODE,
- SRSO_CMD_SAFE_RET,
- SRSO_CMD_IBPB,
- SRSO_CMD_IBPB_ON_VMEXIT,
-};
-
static const char * const srso_strings[] = {
[SRSO_MITIGATION_NONE] = "Vulnerable",
[SRSO_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
@@ -2684,8 +2676,7 @@ static const char * const srso_strings[] = {
[SRSO_MITIGATION_IBPB_ON_VMEXIT] = "Mitigation: IBPB on VMEXIT only"
};
-static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_NONE;
-static enum srso_mitigation_cmd srso_cmd __ro_after_init = SRSO_CMD_SAFE_RET;
+static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO;
static int __init srso_parse_cmdline(char *str)
{
@@ -2693,15 +2684,15 @@ static int __init srso_parse_cmdline(char *str)
return -EINVAL;
if (!strcmp(str, "off"))
- srso_cmd = SRSO_CMD_OFF;
+ srso_mitigation = SRSO_MITIGATION_NONE;
else if (!strcmp(str, "microcode"))
- srso_cmd = SRSO_CMD_MICROCODE;
+ srso_mitigation = SRSO_MITIGATION_MICROCODE;
else if (!strcmp(str, "safe-ret"))
- srso_cmd = SRSO_CMD_SAFE_RET;
+ srso_mitigation = SRSO_MITIGATION_SAFE_RET;
else if (!strcmp(str, "ibpb"))
- srso_cmd = SRSO_CMD_IBPB;
+ srso_mitigation = SRSO_MITIGATION_IBPB;
else if (!strcmp(str, "ibpb-vmexit"))
- srso_cmd = SRSO_CMD_IBPB_ON_VMEXIT;
+ srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
else
pr_err("Ignoring unknown SRSO option (%s).", str);
@@ -2715,13 +2706,15 @@ static void __init srso_select_mitigation(void)
{
bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
- if (!boot_cpu_has_bug(X86_BUG_SRSO) ||
- cpu_mitigations_off() ||
- srso_cmd == SRSO_CMD_OFF) {
- if (boot_cpu_has(X86_FEATURE_SBPB))
- x86_pred_cmd = PRED_CMD_SBPB;
+ if (!boot_cpu_has_bug(X86_BUG_SRSO) || cpu_mitigations_off())
+ srso_mitigation = SRSO_MITIGATION_NONE;
+
+ if (srso_mitigation == SRSO_MITIGATION_NONE)
return;
- }
+
+ /* Default mitigation */
+ if (srso_mitigation == SRSO_MITIGATION_AUTO)
+ srso_mitigation = SRSO_MITIGATION_SAFE_RET;
if (has_microcode) {
/*
@@ -2734,98 +2727,104 @@ static void __init srso_select_mitigation(void)
setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
return;
}
-
- if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
- srso_mitigation = SRSO_MITIGATION_IBPB;
- goto out;
- }
} else {
pr_warn("IBPB-extending microcode not applied!\n");
pr_warn(SRSO_NOTICE);
- /* may be overwritten by SRSO_CMD_SAFE_RET below */
- srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED;
+ /* Fall-back to Safe-RET */
+ srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
}
- switch (srso_cmd) {
- case SRSO_CMD_MICROCODE:
- if (has_microcode) {
- srso_mitigation = SRSO_MITIGATION_MICROCODE;
- pr_warn(SRSO_NOTICE);
- }
+ switch (srso_mitigation) {
+ case SRSO_MITIGATION_MICROCODE:
break;
- case SRSO_CMD_SAFE_RET:
+ case SRSO_MITIGATION_SAFE_RET:
+ case SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED:
if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO))
goto ibpb_on_vmexit;
- if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {
- /*
- * Enable the return thunk for generated code
- * like ftrace, static_call, etc.
- */
- setup_force_cpu_cap(X86_FEATURE_RETHUNK);
- setup_force_cpu_cap(X86_FEATURE_UNRET);
-
- if (boot_cpu_data.x86 == 0x19) {
- setup_force_cpu_cap(X86_FEATURE_SRSO_ALIAS);
- x86_return_thunk = srso_alias_return_thunk;
- } else {
- setup_force_cpu_cap(X86_FEATURE_SRSO);
- x86_return_thunk = srso_return_thunk;
- }
- if (has_microcode)
- srso_mitigation = SRSO_MITIGATION_SAFE_RET;
- else
- srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
- } else {
+ if (!IS_ENABLED(CONFIG_MITIGATION_SRSO))
pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
- }
break;
- case SRSO_CMD_IBPB:
- if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) {
- if (has_microcode) {
- setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
- srso_mitigation = SRSO_MITIGATION_IBPB;
-
- /*
- * IBPB on entry already obviates the need for
- * software-based untraining so clear those in case some
- * other mitigation like Retbleed has selected them.
- */
- setup_clear_cpu_cap(X86_FEATURE_UNRET);
- setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
- }
- } else {
+ case SRSO_MITIGATION_IBPB:
+ if (!IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY))
pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n");
- }
break;
ibpb_on_vmexit:
- case SRSO_CMD_IBPB_ON_VMEXIT:
- if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {
- if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
- setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
- srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
-
- /*
- * There is no need for RSB filling: entry_ibpb() ensures
- * all predictions, including the RSB, are invalidated,
- * regardless of IBPB implementation.
- */
- setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
- }
- } else {
+ case SRSO_MITIGATION_IBPB_ON_VMEXIT:
+ if (!IS_ENABLED(CONFIG_MITIGATION_SRSO))
pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
- }
break;
default:
break;
}
+}
+
+static void __init srso_update_mitigation(void)
+{
+ /* If retbleed is using IBPB, that works for SRSO as well */
+ if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB)
+ srso_mitigation = SRSO_MITIGATION_IBPB;
+
+ if (srso_mitigation != SRSO_MITIGATION_NONE)
+ pr_info("%s\n", srso_strings[srso_mitigation]);
+}
+
+static void __init srso_apply_mitigation(void)
+{
+ if (srso_mitigation == SRSO_MITIGATION_NONE) {
+ if (boot_cpu_has(X86_FEATURE_SBPB))
+ x86_pred_cmd = PRED_CMD_SBPB;
+ return;
+ }
+
+ switch (srso_mitigation) {
+ case SRSO_MITIGATION_SAFE_RET:
+ case SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED:
+ /*
+ * Enable the return thunk for generated code
+ * like ftrace, static_call, etc.
+ */
+ setup_force_cpu_cap(X86_FEATURE_RETHUNK);
+ setup_force_cpu_cap(X86_FEATURE_UNRET);
+
+ if (boot_cpu_data.x86 == 0x19) {
+ setup_force_cpu_cap(X86_FEATURE_SRSO_ALIAS);
+ x86_return_thunk = srso_alias_return_thunk;
+ } else {
+ setup_force_cpu_cap(X86_FEATURE_SRSO);
+ x86_return_thunk = srso_return_thunk;
+ }
+ break;
+
+ case SRSO_MITIGATION_IBPB:
+ setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ /*
+ * IBPB on entry already obviates the need for
+ * software-based untraining so clear those in case some
+ * other mitigation like Retbleed has selected them.
+ */
+ setup_clear_cpu_cap(X86_FEATURE_UNRET);
+ setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
+ break;
+
+ case SRSO_MITIGATION_IBPB_ON_VMEXIT:
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
+ /*
+ * There is no need for RSB filling: entry_ibpb() ensures
+ * all predictions, including the RSB, are invalidated,
+ * regardless of IBPB implementation.
+ */
+ setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
+ break;
+
+ default:
+ break;
+ }
-out:
- pr_info("%s\n", srso_strings[srso_mitigation]);
}
#undef pr_fmt
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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