linux-kernel - [PATCH 1/1] x86/pti: Fix kernel warnings for pti= and nopti cmdline options.

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Message-Id: <20230811213628.40428-2-jo.vanbulck@cs.kuleuven.be>
Date:   Fri, 11 Aug 2023 14:36:28 -0700
From:   Jo Van Bulck <jo.vanbulck@...kuleuven.be>
To:     linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
        luto@...nel.org, peterz@...radead.org, mingo@...hat.com,
        sohil.mehta@...el.com
Cc:     x86@...nel.org, bp@...en8.de, tglx@...utronix.de, hpa@...or.com,
        Jo Van Bulck <jo.vanbulck@...kuleuven.be>
Subject: [PATCH 1/1] x86/pti: Fix kernel warnings for pti= and nopti cmdline options.

Parse the pti= and nopti cmdline options using early_param to fix 'Unknown
kernel command line parameters "nopti", will be passed to user space'
warnings in the kernel log when nopti or pti= are passed to the kernel
cmdline on x86 platforms. Additionally allow the kernel to warn for
malformed pti= options.

Signed-off-by: Jo Van Bulck <jo.vanbulck@...kuleuven.be>
---
 arch/x86/mm/pti.c | 59 +++++++++++++++++++++++++++--------------------
 1 file changed, 34 insertions(+), 25 deletions(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 78414c6d1..da42e75dc 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -69,47 +69,34 @@ static void __init pti_print_if_secure(const char *reason)
 		pr_info("%s\n", reason);
 }
 
+/*
+ * Assume mode is auto unless overridden via cmdline below, where pti= takes
+ * priority over nopti and mitigations=off.
+ */
 static enum pti_mode {
 	PTI_AUTO = 0,
+	PTI_FORCE_AUTO,
 	PTI_FORCE_OFF,
 	PTI_FORCE_ON
 } pti_mode;
 
 void __init pti_check_boottime_disable(void)
 {
-	char arg[5];
-	int ret;
-
-	/* Assume mode is auto unless overridden. */
-	pti_mode = PTI_AUTO;
-
 	if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
 		pti_mode = PTI_FORCE_OFF;
 		pti_print_if_insecure("disabled on XEN PV.");
 		return;
 	}
 
-	ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
-	if (ret > 0)  {
-		if (ret == 3 && !strncmp(arg, "off", 3)) {
-			pti_mode = PTI_FORCE_OFF;
-			pti_print_if_insecure("disabled on command line.");
-			return;
-		}
-		if (ret == 2 && !strncmp(arg, "on", 2)) {
-			pti_mode = PTI_FORCE_ON;
-			pti_print_if_secure("force enabled on command line.");
-			goto enable;
-		}
-		if (ret == 4 && !strncmp(arg, "auto", 4)) {
-			pti_mode = PTI_AUTO;
-			goto autosel;
-		}
+	if (pti_mode == PTI_FORCE_ON) {
+		pti_print_if_secure("force enabled on command line.");
+		goto enable;
 	}
-
-	if (cmdline_find_option_bool(boot_command_line, "nopti") ||
-	    cpu_mitigations_off()) {
+	if (pti_mode == PTI_FORCE_AUTO)
+		goto autosel;
+	if (cpu_mitigations_off())
 		pti_mode = PTI_FORCE_OFF;
+	if (pti_mode == PTI_FORCE_OFF) {
 		pti_print_if_insecure("disabled on command line.");
 		return;
 	}
@@ -121,6 +108,28 @@ void __init pti_check_boottime_disable(void)
 	setup_force_cpu_cap(X86_FEATURE_PTI);
 }
 
+static int __init pti_parse_cmdline(char *arg)
+{
+	if (!strcmp(arg, "off"))
+		pti_mode = PTI_FORCE_OFF;
+	else if (!strcmp(arg, "on"))
+		pti_mode = PTI_FORCE_ON;
+	else if (!strcmp(arg, "auto"))
+		pti_mode = PTI_FORCE_AUTO;
+	else
+		return -EINVAL;
+	return 0;
+}
+early_param("pti", pti_parse_cmdline);
+
+static int __init pti_parse_cmdline_nopti(char *arg)
+{
+	if (cmdline_find_option(boot_command_line, "pti", NULL, 0) == -1)
+		pti_mode = PTI_FORCE_OFF;
+	return 0;
+}
+early_param("nopti", pti_parse_cmdline_nopti);
+
 pgd_t __pti_set_user_pgtbl(pgd_t *pgdp, pgd_t pgd)
 {
 	/*
-- 
2.25.1