x86/its: Add support for RSB stuffing mitigation

When retpoline mitigation is enabled for spectre-v2, enabling
call-depth-tracking and RSB stuffing also mitigates ITS. Add cmdline option
indirect_target_selection=stuff to allow enabling RSB stuffing mitigation.

When retpoline mitigation is not enabled, =stuff option is ignored, and
default mitigation for ITS is deployed.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e70d15095f28b479624e63e49a8392475aae7ff7..8f75ec17739944a9e886604e40412eadbefaa27b 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2212,6 +2212,9 @@
                                mitigation.
                        vmexit: Only deploy mitigation if CPU is affected by
                                guest/host isolation part of ITS.
+                       stuff:  Deploy RSB-fill mitigation when retpoline is
+                               also deployed. Otherwise, deploy the default
+                               mitigation.
 
                        For details see:
                        Documentation/admin-guide/hw-vuln/indirect-target-selection.rst

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index e919d645d83031c4f88c5b6483786eda13500663..c6dcc03a43da698d4db47507641531f0244e4cea 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1204,6 +1204,7 @@ enum its_mitigation_cmd {
        ITS_CMD_OFF,
        ITS_CMD_ON,
        ITS_CMD_VMEXIT,
+       ITS_CMD_RSB_STUFF,
 };
 
 enum its_mitigation {
@@ -1244,6 +1245,8 @@ static int __init its_parse_cmdline(char *str)
                setup_force_cpu_bug(X86_BUG_ITS);
        } else if (!strcmp(str, "vmexit")) {
                its_cmd = ITS_CMD_VMEXIT;
+       } else if (!strcmp(str, "stuff")) {
+               its_cmd = ITS_CMD_RSB_STUFF;
        } else {
                pr_err("Ignoring unknown indirect_target_selection option (%s).", str);
        }
@@ -1295,6 +1298,12 @@ static void __init its_select_mitigation(void)
                goto out;
        }
 
+       if (cmd == ITS_CMD_RSB_STUFF &&
+           (!boot_cpu_has(X86_FEATURE_RETPOLINE) || !IS_ENABLED(CONFIG_MITIGATION_CALL_DEPTH_TRACKING))) {
+               pr_err("RSB stuff mitigation not supported, using default\n");
+               cmd = ITS_CMD_ON;
+       }
+
        switch (cmd) {
        case ITS_CMD_OFF:
                its_mitigation = ITS_MITIGATION_OFF;
@@ -1312,6 +1321,16 @@ static void __init its_select_mitigation(void)
                setup_force_cpu_cap(X86_FEATURE_RETHUNK);
                set_return_thunk(its_return_thunk);
                break;
+       case ITS_CMD_RSB_STUFF:
+               its_mitigation = ITS_MITIGATION_RETPOLINE_STUFF;
+               setup_force_cpu_cap(X86_FEATURE_RETHUNK);
+               setup_force_cpu_cap(X86_FEATURE_CALL_DEPTH);
+               set_return_thunk(call_depth_return_thunk);
+               if (retbleed_mitigation == RETBLEED_MITIGATION_NONE) {
+                       retbleed_mitigation = RETBLEED_MITIGATION_STUFF;
+                       pr_info("Retbleed mitigation updated to stuffing\n");
+               }
+               break;
        }
 out:
        pr_info("%s\n", its_strings[its_mitigation]);