Commit b0845ce5 authored by Mark Rutland's avatar Mark Rutland Committed by Linus Torvalds
Browse files

kasan: report only the first error by default 

Disable kasan after the first report.  There are several reasons for
this:

 - Single bug quite often has multiple invalid memory accesses causing
   storm in the dmesg.

 - Write OOB access might corrupt metadata so the next report will print
   bogus alloc/free stacktraces.

 - Reports after the first easily could be not bugs by itself but just
   side effects of the first one.

Given that multiple reports usually only do harm, it makes sense to
disable kasan after the first one.  If user wants to see all the
reports, the boot-time parameter kasan_multi_shot must be used.

[aryabinin@virtuozzo.com: wrote changelog and doc, added missing include]
Link: http://lkml.kernel.org/r/20170323154416.30257-1-aryabinin@virtuozzo.com


Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4742a35d

Documentation/admin-guide/kernel-parameters.txt

+6 −0
Original line number Diff line number Diff line
@@ -1725,6 +1725,12 @@ 
			kernel and module base offset ASLR (Address Space

			Layout Randomization).



	kasan_multi_shot

			[KNL] Enforce KASAN (Kernel Address Sanitizer) to print

			report on every invalid memory access. Without this

			parameter KASAN will print report only for the first

			invalid access.



	keepinitrd	[HW,ARM]



	kernelcore=	[KNL,X86,IA-64,PPC]

include/linux/kasan.h

+3 −0
Original line number Diff line number Diff line
@@ -76,6 +76,9 @@ size_t ksize(const void *); 
static inline void kasan_unpoison_slab(const void *ptr) { ksize(ptr); }

size_t kasan_metadata_size(struct kmem_cache *cache);



bool kasan_save_enable_multi_shot(void);

void kasan_restore_multi_shot(bool enabled);



#else /* CONFIG_KASAN */



static inline void kasan_unpoison_shadow(const void *address, size_t size) {}

lib/test_kasan.c

+10 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
#include <linux/string.h>

#include <linux/uaccess.h>

#include <linux/module.h>

#include <linux/kasan.h>



/*

 * Note: test functions are marked noinline so that their names appear in
@@ -474,6 +475,12 @@ static noinline void __init use_after_scope_test(void) 


static int __init kmalloc_tests_init(void)

{

	/*

	 * Temporarily enable multi-shot mode. Otherwise, we'd only get a

	 * report for the first case.

	 */

	bool multishot = kasan_save_enable_multi_shot();



	kmalloc_oob_right();

	kmalloc_oob_left();

	kmalloc_node_oob_right();
@@ -499,6 +506,9 @@ static int __init kmalloc_tests_init(void) 
	ksize_unpoisons_memory();

	copy_user_test();

	use_after_scope_test();



	kasan_restore_multi_shot(multishot);



	return -EAGAIN;

}

mm/kasan/kasan.h

+0 −5
Original line number Diff line number Diff line
@@ -96,11 +96,6 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr) 
		<< KASAN_SHADOW_SCALE_SHIFT);

}



static inline bool kasan_report_enabled(void)

{

	return !current->kasan_depth;

}



void kasan_report(unsigned long addr, size_t size,

		bool is_write, unsigned long ip);

void kasan_report_double_free(struct kmem_cache *cache, void *object,

mm/kasan/report.c

+36 −0
Original line number Diff line number Diff line
@@ -13,7 +13,9 @@ 
 *

 */



#include <linux/bitops.h>

#include <linux/ftrace.h>

#include <linux/init.h>

#include <linux/kernel.h>

#include <linux/mm.h>

#include <linux/printk.h>
@@ -293,6 +295,40 @@ static void kasan_report_error(struct kasan_access_info *info) 
	kasan_end_report(&flags);

}



static unsigned long kasan_flags;



#define KASAN_BIT_REPORTED	0

#define KASAN_BIT_MULTI_SHOT	1



bool kasan_save_enable_multi_shot(void)

{

	return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);

}

EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);



void kasan_restore_multi_shot(bool enabled)

{

	if (!enabled)

		clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);

}

EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);



static int __init kasan_set_multi_shot(char *str)

{

	set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);

	return 1;

}

__setup("kasan_multi_shot", kasan_set_multi_shot);



static inline bool kasan_report_enabled(void)

{

	if (current->kasan_depth)

		return false;

	if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))

		return true;

	return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);

}



void kasan_report(unsigned long addr, size_t size,

		bool is_write, unsigned long ip)

{

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