x86/bugs: Restructure SSB mitigation

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

Remove __ssb_select_mitigation() and split the functionality between the
select/apply functions.

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/20250418161721.1855190-15-david.kaplan@amd.com

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 93d07438eea78e06fffd32bf4a7cb2e19191b6d2..fbb4f1378de1fce6a31b24d5139f866e9501aece 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -65,6 +65,7 @@ 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 ssb_apply_mitigation(void);
 static void __init l1tf_select_mitigation(void);
 static void __init mds_select_mitigation(void);
 static void __init mds_update_mitigation(void);
@@ -243,6 +244,7 @@ void __init cpu_select_mitigations(void)
        spectre_v2_apply_mitigation();
        retbleed_apply_mitigation();
        spectre_v2_user_apply_mitigation();
+       ssb_apply_mitigation();
        mds_apply_mitigation();
        taa_apply_mitigation();
        mmio_apply_mitigation();
@@ -2219,19 +2221,18 @@ static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void)
        return cmd;
 }
 
-static enum ssb_mitigation __init __ssb_select_mitigation(void)
+static void __init ssb_select_mitigation(void)
 {
-       enum ssb_mitigation mode = SPEC_STORE_BYPASS_NONE;
        enum ssb_mitigation_cmd cmd;
 
        if (!boot_cpu_has(X86_FEATURE_SSBD))
-               return mode;
+               goto out;
 
        cmd = ssb_parse_cmdline();
        if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS) &&
            (cmd == SPEC_STORE_BYPASS_CMD_NONE ||
             cmd == SPEC_STORE_BYPASS_CMD_AUTO))
-               return mode;
+               return;
 
        switch (cmd) {
        case SPEC_STORE_BYPASS_CMD_SECCOMP:
@@ -2240,28 +2241,35 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
                 * enabled.
                 */
                if (IS_ENABLED(CONFIG_SECCOMP))
-                       mode = SPEC_STORE_BYPASS_SECCOMP;
+                       ssb_mode = SPEC_STORE_BYPASS_SECCOMP;
                else
-                       mode = SPEC_STORE_BYPASS_PRCTL;
+                       ssb_mode = SPEC_STORE_BYPASS_PRCTL;
                break;
        case SPEC_STORE_BYPASS_CMD_ON:
-               mode = SPEC_STORE_BYPASS_DISABLE;
+               ssb_mode = SPEC_STORE_BYPASS_DISABLE;
                break;
        case SPEC_STORE_BYPASS_CMD_AUTO:
        case SPEC_STORE_BYPASS_CMD_PRCTL:
-               mode = SPEC_STORE_BYPASS_PRCTL;
+               ssb_mode = SPEC_STORE_BYPASS_PRCTL;
                break;
        case SPEC_STORE_BYPASS_CMD_NONE:
                break;
        }
 
+out:
+       if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
+               pr_info("%s\n", ssb_strings[ssb_mode]);
+}
+
+static void __init ssb_apply_mitigation(void)
+{
        /*
         * We have three CPU feature flags that are in play here:
         *  - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible.
         *  - X86_FEATURE_SSBD - CPU is able to turn off speculative store bypass
         *  - X86_FEATURE_SPEC_STORE_BYPASS_DISABLE - engage the mitigation
         */
-       if (mode == SPEC_STORE_BYPASS_DISABLE) {
+       if (ssb_mode == SPEC_STORE_BYPASS_DISABLE) {
                setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE);
                /*
                 * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may
@@ -2275,16 +2283,6 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
                        update_spec_ctrl(x86_spec_ctrl_base);
                }
        }
-
-       return mode;
-}
-
-static void ssb_select_mitigation(void)
-{
-       ssb_mode = __ssb_select_mitigation();
-
-       if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
-               pr_info("%s\n", ssb_strings[ssb_mode]);
 }
 
 #undef pr_fmt