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

From: Jo Van Bulck
Date: Fri Aug 11 2023 - 17:37:46 EST


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@xxxxxxxxxxxxxx>
---
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