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Subject[PATCH mm v3 34/38] kasan: add kasan.vmalloc command line flag
Date
From: Andrey Konovalov <andreyknvl@google.com>

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 <andreyknvl@google.com>

---

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 6f7ed8e3180c..a595f0d88f41 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;
+ }
+
switch (kasan_arg_stacktrace) {
case KASAN_ARG_STACKTRACE_DEFAULT:
/* Default to enabling stack trace collection. */
@@ -184,8 +223,9 @@ void __init kasan_init_hw_tags(void)
break;
}

- pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, stacktrace=%s)\n",
+ pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, vmalloc=%s, stacktrace=%s)\n",
kasan_mode_info(),
+ kasan_vmalloc_enabled() ? "on" : "off",
kasan_stack_collection_enabled() ? "on" : "off");
}

@@ -218,6 +258,9 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
u8 tag;
unsigned long redzone_start, redzone_size;

+ if (!kasan_vmalloc_enabled())
+ return (void *)start;
+
if (!is_vmalloc_or_module_addr(start))
return (void *)start;

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 020f3e57a03f..49a5d5e2e948 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -12,6 +12,7 @@
#include <linux/static_key.h>
#include "../slab.h"

+DECLARE_STATIC_KEY_FALSE(kasan_flag_vmalloc);
DECLARE_STATIC_KEY_FALSE(kasan_flag_stacktrace);

enum kasan_mode {
@@ -22,6 +23,11 @@ enum kasan_mode {

extern enum kasan_mode kasan_mode __ro_after_init;

+static inline bool kasan_vmalloc_enabled(void)
+{
+ return static_branch_likely(&kasan_flag_vmalloc);
+}
+
static inline bool kasan_stack_collection_enabled(void)
{
return static_branch_unlikely(&kasan_flag_stacktrace);
--
2.25.1
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