Commit facd226f authored by Pawan Gupta's avatar Pawan Gupta Committed by Dave Hansen
Browse files

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: default avatarPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: default avatarAlexandre Chartre <alexandre.chartre@oracle.com>
parent 2665281a

Documentation/admin-guide/kernel-parameters.txt

+3 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/cpu/bugs.c

+19 −0
Original line number Diff line number Diff line
@@ -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]);