From: Andrey Konovalov <redacted>

Allow disabling vmalloc() tagging for HW_TAGS KASAN via a kasan.vmalloc
command line switch.

This is a fail-safe switch intended for production systems that enable
HW_TAGS KASAN. In case vmalloc() tagging ends up having an issue not
detected during testing but that manifests in production, kasan.vmalloc
allows to turn vmalloc() tagging off while leaving page_alloc/slab
tagging on.

Signed-off-by: Andrey Konovalov <redacted>

---

Changes v1->v2:
- Mark kasan_arg_stacktrace as __initdata instead of __ro_after_init.
- Combine KASAN_ARG_VMALLOC_DEFAULT and KASAN_ARG_VMALLOC_ON switch
  cases.
---
 mm/kasan/hw_tags.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
 mm/kasan/kasan.h   |  6 ++++++
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 99230e666c1b..657b23cebe28 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c

@@ -32,6 +32,12 @@ enum kasan_arg_mode {
        KASAN_ARG_MODE_ASYMM,
 };

+enum kasan_arg_vmalloc {
+       KASAN_ARG_VMALLOC_DEFAULT,
+       KASAN_ARG_VMALLOC_OFF,
+       KASAN_ARG_VMALLOC_ON,
+};
+
 enum kasan_arg_stacktrace {
        KASAN_ARG_STACKTRACE_DEFAULT,
        KASAN_ARG_STACKTRACE_OFF,

@@ -40,6 +46,7 @@ enum kasan_arg_stacktrace {

 static enum kasan_arg kasan_arg __ro_after_init;
 static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
+static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
 static enum kasan_arg_stacktrace kasan_arg_stacktrace __initdata;

 /* Whether KASAN is enabled at all. */

@@ -50,6 +57,9 @@ EXPORT_SYMBOL(kasan_flag_enabled);
 enum kasan_mode kasan_mode __ro_after_init;
 EXPORT_SYMBOL_GPL(kasan_mode);

+/* Whether to enable vmalloc tagging. */
+DEFINE_STATIC_KEY_FALSE(kasan_flag_vmalloc);
+
 /* Whether to collect alloc/free stack traces. */
 DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);

@@ -89,6 +99,23 @@ static int __init early_kasan_mode(char *arg)
 }
 early_param("kasan.mode", early_kasan_mode);

+/* kasan.vmalloc=off/on */
+static int __init early_kasan_flag_vmalloc(char *arg)
+{
+       if (!arg)
+               return -EINVAL;
+
+       if (!strcmp(arg, "off"))
+               kasan_arg_vmalloc = KASAN_ARG_VMALLOC_OFF;
+       else if (!strcmp(arg, "on"))
+               kasan_arg_vmalloc = KASAN_ARG_VMALLOC_ON;
+       else
+               return -EINVAL;
+
+       return 0;
+}
+early_param("kasan.vmalloc", early_kasan_flag_vmalloc);
+
 /* kasan.stacktrace=off/on */
 static int __init early_kasan_flag_stacktrace(char *arg)
 {

@@ -172,6 +199,18 @@ void __init kasan_init_hw_tags(void)
                break;
        }

+       switch (kasan_arg_vmalloc) {
+       case KASAN_ARG_VMALLOC_DEFAULT:
+               /* Default to enabling vmalloc tagging. */
+               fallthrough;
+       case KASAN_ARG_VMALLOC_ON:
+               static_branch_enable(&kasan_flag_vmalloc);
+               break;
+       case KASAN_ARG_VMALLOC_OFF:
+               /* Do nothing, kasan_flag_vmalloc keeps its default value. */
+               break;
+       }