[52/60] kasan: add and integrate kasan boot parameters

Commit Message

Andrew Morton Dec. 22, 2020, 8:03 p.m. UTC

From: Andrey Konovalov <[e-mail]>
Subject: kasan: add and integrate kasan boot parameters

Hardware tag-based KASAN mode is intended to eventually be used in
production as a security mitigation. Therefore there's a need for finer
control over KASAN features and for an existence of a kill switch.

This change adds a few boot parameters for hardware tag-based KASAN that
allow to disable or otherwise control particular KASAN features.

The features that can be controlled are:

1. Whether KASAN is enabled at all.
2. Whether KASAN collects and saves alloc/free stacks.
3. Whether KASAN panics on a detected bug or not.

With this change a new boot parameter kasan.mode allows to choose one of
three main modes:

- kasan.mode=off - KASAN is disabled, no tag checks are performed
- kasan.mode=prod - only essential production features are enabled
- kasan.mode=full - all KASAN features are enabled

The chosen mode provides default control values for the features mentioned
above. However it's also possible to override the default values by
providing:

- kasan.stacktrace=off/on - enable alloc/free stack collection
                            (default: on for mode=full, otherwise off)
- kasan.fault=report/panic - only report tag fault or also panic
                             (default: report)

If kasan.mode parameter is not provided, it defaults to full when
CONFIG_DEBUG_KERNEL is enabled, and to prod otherwise.

It is essential that switching between these modes doesn't require
rebuilding the kernel with different configs, as this is required by
the Android GKI (Generic Kernel Image) initiative [1].

[1] https://source.android.com/devices/architecture/kernel/generic-kernel-image

[[e-mail]: don't use read-only static keys]
  Link: https://lkml.kernel.org/r/f2[e-mail]
Link: https://lkml.kernel.org/r/cb[e-mail]
Link: https://linux-review.googlesource.com/id/If7d37003875b2ed3e0935702c8015c223d6416a4
Signed-off-by: Andrey Konovalov <[e-mail]>
Reviewed-by: Marco Elver <[e-mail]>
Reviewed-by: Dmitry Vyukov <[e-mail]>
Tested-by: Vincenzo Frascino <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Branislav Rankov <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Evgenii Stepanov <[e-mail]>
Cc: Kevin Brodsky <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/kasan/common.c  |   22 ++++--
 mm/kasan/hw_tags.c |  151 +++++++++++++++++++++++++++++++++++++++++++
 mm/kasan/kasan.h   |   16 ++++
 mm/kasan/report.c  |   14 +++
 4 files changed, 196 insertions(+), 7 deletions(-)

Patch

--- a/mm/kasan/common.c~kasan-add-and-integrate-kasan-boot-parameters
+++ a/mm/kasan/common.c
@@ -134,6 +134,11 @@  void kasan_cache_create(struct kmem_cach
 	unsigned int redzone_size;
 	int redzone_adjust;
 
+	if (!kasan_stack_collection_enabled()) {
+		*flags |= SLAB_KASAN;
+		return;
+	}
+
 	/* Add alloc meta. */
 	cache->kasan_info.alloc_meta_offset = *size;
 	*size += sizeof(struct kasan_alloc_meta);
@@ -170,6 +175,8 @@  void kasan_cache_create(struct kmem_cach
 
 size_t kasan_metadata_size(struct kmem_cache *cache)
 {
+	if (!kasan_stack_collection_enabled())
+		return 0;
 	return (cache->kasan_info.alloc_meta_offset ?
 		sizeof(struct kasan_alloc_meta) : 0) +
 		(cache->kasan_info.free_meta_offset ?
@@ -262,11 +269,13 @@  void * __must_check kasan_init_slab_obj(
 {
 	struct kasan_alloc_meta *alloc_meta;
 
-	if (!(cache->flags & SLAB_KASAN))
-		return (void *)object;
+	if (kasan_stack_collection_enabled()) {
+		if (!(cache->flags & SLAB_KASAN))
+			return (void *)object;
 
-	alloc_meta = kasan_get_alloc_meta(cache, object);
-	__memset(alloc_meta, 0, sizeof(*alloc_meta));
+		alloc_meta = kasan_get_alloc_meta(cache, object);
+		__memset(alloc_meta, 0, sizeof(*alloc_meta));
+	}
 
 	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
 		object = set_tag(object, assign_tag(cache, object, true, false));
@@ -303,6 +312,9 @@  static bool __kasan_slab_free(struct kme
 	rounded_up_size = round_up(cache->object_size, KASAN_GRANULE_SIZE);
 	poison_range(object, rounded_up_size, KASAN_KMALLOC_FREE);
 
+	if (!kasan_stack_collection_enabled())
+		return false;
+
 	if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
 			unlikely(!(cache->flags & SLAB_KASAN)))
 		return false;
@@ -350,7 +362,7 @@  static void *__kasan_kmalloc(struct kmem
 	poison_range((void *)redzone_start, redzone_end - redzone_start,
 		     KASAN_KMALLOC_REDZONE);
 
-	if (cache->flags & SLAB_KASAN)
+	if (kasan_stack_collection_enabled() && (cache->flags & SLAB_KASAN))
 		set_alloc_info(cache, (void *)object, flags);
 
 	return set_tag(object, tag);
--- a/mm/kasan/hw_tags.c~kasan-add-and-integrate-kasan-boot-parameters
+++ a/mm/kasan/hw_tags.c
@@ -8,18 +8,115 @@ 
 
 #define pr_fmt(fmt) "kasan: " fmt
 
+#include <linux/init.h>
 #include <linux/kasan.h>
 #include <linux/kernel.h>
 #include <linux/memory.h>
 #include <linux/mm.h>
+#include <linux/static_key.h>
 #include <linux/string.h>
 #include <linux/types.h>
 
 #include "kasan.h"
 
+enum kasan_arg_mode {
+	KASAN_ARG_MODE_DEFAULT,
+	KASAN_ARG_MODE_OFF,
+	KASAN_ARG_MODE_PROD,
+	KASAN_ARG_MODE_FULL,
+};
+
+enum kasan_arg_stacktrace {
+	KASAN_ARG_STACKTRACE_DEFAULT,
+	KASAN_ARG_STACKTRACE_OFF,
+	KASAN_ARG_STACKTRACE_ON,
+};
+
+enum kasan_arg_fault {
+	KASAN_ARG_FAULT_DEFAULT,
+	KASAN_ARG_FAULT_REPORT,
+	KASAN_ARG_FAULT_PANIC,
+};
+
+static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
+static enum kasan_arg_stacktrace kasan_arg_stacktrace __ro_after_init;
+static enum kasan_arg_fault kasan_arg_fault __ro_after_init;
+
+/* Whether KASAN is enabled at all. */
+DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
+EXPORT_SYMBOL(kasan_flag_enabled);
+
+/* Whether to collect alloc/free stack traces. */
+DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
+
+/* Whether panic or disable tag checking on fault. */
+bool kasan_flag_panic __ro_after_init;
+
+/* kasan.mode=off/prod/full */
+static int __init early_kasan_mode(char *arg)
+{
+	if (!arg)
+		return -EINVAL;
+
+	if (!strcmp(arg, "off"))
+		kasan_arg_mode = KASAN_ARG_MODE_OFF;
+	else if (!strcmp(arg, "prod"))
+		kasan_arg_mode = KASAN_ARG_MODE_PROD;
+	else if (!strcmp(arg, "full"))
+		kasan_arg_mode = KASAN_ARG_MODE_FULL;
+	else
+		return -EINVAL;
+
+	return 0;
+}
+early_param("kasan.mode", early_kasan_mode);
+
+/* kasan.stack=off/on */
+static int __init early_kasan_flag_stacktrace(char *arg)
+{
+	if (!arg)
+		return -EINVAL;
+
+	if (!strcmp(arg, "off"))
+		kasan_arg_stacktrace = KASAN_ARG_STACKTRACE_OFF;
+	else if (!strcmp(arg, "on"))
+		kasan_arg_stacktrace = KASAN_ARG_STACKTRACE_ON;
+	else
+		return -EINVAL;
+
+	return 0;
+}
+early_param("kasan.stacktrace", early_kasan_flag_stacktrace);
+
+/* kasan.fault=report/panic */
+static int __init early_kasan_fault(char *arg)
+{
+	if (!arg)
+		return -EINVAL;
+
+	if (!strcmp(arg, "report"))
+		kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
+	else if (!strcmp(arg, "panic"))
+		kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
+	else
+		return -EINVAL;
+
+	return 0;
+}
+early_param("kasan.fault", early_kasan_fault);
+
 /* kasan_init_hw_tags_cpu() is called for each CPU. */
 void kasan_init_hw_tags_cpu(void)
 {
+	/*
+	 * There's no need to check that the hardware is MTE-capable here,
+	 * as this function is only called for MTE-capable hardware.
+	 */
+
+	/* If KASAN is disabled, do nothing. */
+	if (kasan_arg_mode == KASAN_ARG_MODE_OFF)
+		return;
+
 	hw_init_tags(KASAN_TAG_MAX);
 	hw_enable_tagging();
 }
@@ -27,6 +124,60 @@  void kasan_init_hw_tags_cpu(void)
 /* kasan_init_hw_tags() is called once on boot CPU. */
 void __init kasan_init_hw_tags(void)
 {
+	/* If hardware doesn't support MTE, do nothing. */
+	if (!system_supports_mte())
+		return;
+
+	/* Choose KASAN mode if kasan boot parameter is not provided. */
+	if (kasan_arg_mode == KASAN_ARG_MODE_DEFAULT) {
+		if (IS_ENABLED(CONFIG_DEBUG_KERNEL))
+			kasan_arg_mode = KASAN_ARG_MODE_FULL;
+		else
+			kasan_arg_mode = KASAN_ARG_MODE_PROD;
+	}
+
+	/* Preset parameter values based on the mode. */
+	switch (kasan_arg_mode) {
+	case KASAN_ARG_MODE_DEFAULT:
+		/* Shouldn't happen as per the check above. */
+		WARN_ON(1);
+		return;
+	case KASAN_ARG_MODE_OFF:
+		/* If KASAN is disabled, do nothing. */
+		return;
+	case KASAN_ARG_MODE_PROD:
+		static_branch_enable(&kasan_flag_enabled);
+		break;
+	case KASAN_ARG_MODE_FULL:
+		static_branch_enable(&kasan_flag_enabled);
+		static_branch_enable(&kasan_flag_stacktrace);
+		break;
+	}
+
+	/* Now, optionally override the presets. */
+
+	switch (kasan_arg_stacktrace) {
+	case KASAN_ARG_STACKTRACE_DEFAULT:
+		break;
+	case KASAN_ARG_STACKTRACE_OFF:
+		static_branch_disable(&kasan_flag_stacktrace);
+		break;
+	case KASAN_ARG_STACKTRACE_ON:
+		static_branch_enable(&kasan_flag_stacktrace);
+		break;
+	}
+
+	switch (kasan_arg_fault) {
+	case KASAN_ARG_FAULT_DEFAULT:
+		break;
+	case KASAN_ARG_FAULT_REPORT:
+		kasan_flag_panic = false;
+		break;
+	case KASAN_ARG_FAULT_PANIC:
+		kasan_flag_panic = true;
+		break;
+	}
+
 	pr_info("KernelAddressSanitizer initialized\n");
 }
 
--- a/mm/kasan/kasan.h~kasan-add-and-integrate-kasan-boot-parameters
+++ a/mm/kasan/kasan.h
@@ -5,6 +5,22 @@ 
 #include <linux/kasan.h>
 #include <linux/stackdepot.h>
 
+#ifdef CONFIG_KASAN_HW_TAGS
+#include <linux/static_key.h>
+DECLARE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
+static inline bool kasan_stack_collection_enabled(void)
+{
+	return static_branch_unlikely(&kasan_flag_stacktrace);
+}
+#else
+static inline bool kasan_stack_collection_enabled(void)
+{
+	return true;
+}
+#endif
+
+extern bool kasan_flag_panic __ro_after_init;
+
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 #define KASAN_GRANULE_SIZE	(1UL << KASAN_SHADOW_SCALE_SHIFT)
 #else
--- a/mm/kasan/report.c~kasan-add-and-integrate-kasan-boot-parameters
+++ a/mm/kasan/report.c
@@ -99,6 +99,10 @@  static void end_report(unsigned long *fl
 		panic_on_warn = 0;
 		panic("panic_on_warn set ...\n");
 	}
+#ifdef CONFIG_KASAN_HW_TAGS
+	if (kasan_flag_panic)
+		panic("kasan.fault=panic set ...\n");
+#endif
 	kasan_enable_current();
 }
 
@@ -161,8 +165,8 @@  static void describe_object_addr(struct
 		(void *)(object_addr + cache->object_size));
 }
 
-static void describe_object(struct kmem_cache *cache, void *object,
-				const void *addr, u8 tag)
+static void describe_object_stacks(struct kmem_cache *cache, void *object,
+					const void *addr, u8 tag)
 {
 	struct kasan_alloc_meta *alloc_meta = kasan_get_alloc_meta(cache, object);
 
@@ -190,7 +194,13 @@  static void describe_object(struct kmem_
 		}
 #endif
 	}
+}
 
+static void describe_object(struct kmem_cache *cache, void *object,
+				const void *addr, u8 tag)
+{
+	if (kasan_stack_collection_enabled())
+		describe_object_stacks(cache, object, addr, tag);
 	describe_object_addr(cache, object, addr);
 }