x86/bugs: Fix spectre_v2 forcing

There were two oddities with spectre_v2 command line options.

First, any option other than 'off' or 'auto' would force spectre_v2
mitigations even if the CPU (hypothetically) wasn't vulnerable to spectre_v2.
That was inconsistent with all the other bugs where mitigations are ignored
unless an explicit 'force' option is specified.

Second, even though spectre_v2 mitigations would be enabled in these cases,
the X86_BUG_SPECTRE_V2 bit wasn't set.  This is again inconsistent with the
forcing behavior of other bugs and arguably incorrect as it doesn't make sense
to enable a mitigation if the X86_BUG bit isn't set.

Fix both issues by only forcing spectre_v2 mitigations when the
'spectre_v2=on' option is specified (which was already called
SPECTRE_V2_CMD_FORCE) and setting the relevant X86_BUG_* bits in that case.

This also allows for simplifying bhi_update_mitigation() because
spectre_v2_cmd will now always be SPECTRE_V2_CMD_NONE if the CPU is immune to
spectre_v2.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250915134706.3201818-1-david.kaplan@amd.com

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f28a7383b88bdbc54dd05f89149b0b12e287d154..145f8777aa32d41902835c17792ebdabbb897268 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2057,29 +2057,32 @@ static int __init spectre_v2_parse_cmdline(char *str)
        if (nospectre_v2)
                return 0;
 
-       if (!strcmp(str, "off"))
+       if (!strcmp(str, "off")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_NONE;
-       else if (!strcmp(str, "on"))
+       } else if (!strcmp(str, "on")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_FORCE;
-       else if (!strcmp(str, "retpoline"))
+               setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
+               setup_force_cpu_bug(X86_BUG_SPECTRE_V2_USER);
+       } else if (!strcmp(str, "retpoline")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_RETPOLINE;
-       else if (!strcmp(str, "retpoline,amd") ||
-                !strcmp(str, "retpoline,lfence"))
+       } else if (!strcmp(str, "retpoline,amd") ||
+                !strcmp(str, "retpoline,lfence")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_RETPOLINE_LFENCE;
-       else if (!strcmp(str, "retpoline,generic"))
+       } else if (!strcmp(str, "retpoline,generic")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_RETPOLINE_GENERIC;
-       else if (!strcmp(str, "eibrs"))
+       } else if (!strcmp(str, "eibrs")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_EIBRS;
-       else if (!strcmp(str, "eibrs,lfence"))
+       } else if (!strcmp(str, "eibrs,lfence")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_EIBRS_LFENCE;
-       else if (!strcmp(str, "eibrs,retpoline"))
+       } else if (!strcmp(str, "eibrs,retpoline")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_EIBRS_RETPOLINE;
-       else if (!strcmp(str, "auto"))
+       } else if (!strcmp(str, "auto")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
-       else if (!strcmp(str, "ibrs"))
+       } else if (!strcmp(str, "ibrs")) {
                spectre_v2_cmd = SPECTRE_V2_CMD_IBRS;
-       else
+       } else {
                pr_err("Ignoring unknown spectre_v2 option (%s).", str);
+       }
 
        return 0;
 }
@@ -2232,10 +2235,6 @@ static void __init bhi_update_mitigation(void)
 {
        if (spectre_v2_cmd == SPECTRE_V2_CMD_NONE)
                bhi_mitigation = BHI_MITIGATION_OFF;
-
-       if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) &&
-            spectre_v2_cmd == SPECTRE_V2_CMD_AUTO)
-               bhi_mitigation = BHI_MITIGATION_OFF;
 }
 
 static void __init bhi_apply_mitigation(void)
@@ -2316,9 +2315,10 @@ static void __init spectre_v2_select_mitigation(void)
                spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
        }
 
-       if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) &&
-           (spectre_v2_cmd == SPECTRE_V2_CMD_NONE || spectre_v2_cmd == SPECTRE_V2_CMD_AUTO))
+       if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2)) {
+               spectre_v2_cmd = SPECTRE_V2_CMD_NONE;
                return;
+       }
 
        switch (spectre_v2_cmd) {
        case SPECTRE_V2_CMD_NONE: