Re: [PATCH v2 33/37] kasan, arm64: implement HW_TAGS runtime

[Marco Elver <elver@google.com>]

[ Sorry for the additional email on this patch; trying to consolidate
  comments now. ]

On Tue, Sep 15, 2020 at 11:16PM +0200, Andrey Konovalov wrote:
> Provide implementation of KASAN functions required for the hardware
> tag-based mode. Those include core functions for memory and pointer
> tagging (tags_hw.c) and bug reporting (report_tags_hw.c). Also adapt
> common KASAN code to support the new mode.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> ---
> Change-Id: I8a8689ba098174a4d0ef3f1d008178387c80ee1c
> ---
>  arch/arm64/include/asm/memory.h   |  4 +-
>  arch/arm64/kernel/setup.c         |  1 -
>  include/linux/kasan.h             |  6 +--
>  include/linux/mm.h                |  2 +-
>  include/linux/page-flags-layout.h |  2 +-
>  mm/kasan/Makefile                 |  5 ++
>  mm/kasan/common.c                 | 14 +++---
>  mm/kasan/kasan.h                  | 17 +++++--
>  mm/kasan/report_tags_hw.c         | 47 +++++++++++++++++++
>  mm/kasan/report_tags_sw.c         |  2 +-
>  mm/kasan/shadow.c                 |  2 +-
>  mm/kasan/tags_hw.c                | 78 +++++++++++++++++++++++++++++++
>  mm/kasan/tags_sw.c                |  2 +-
>  13 files changed, 162 insertions(+), 20 deletions(-)
>  create mode 100644 mm/kasan/report_tags_hw.c
>  create mode 100644 mm/kasan/tags_hw.c
[...]
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 41c7f1105eaa..412a23d1546b 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -118,7 +118,7 @@ void kasan_free_pages(struct page *page, unsigned int order)
>   */
>  static inline unsigned int optimal_redzone(unsigned int object_size)
>  {
> -	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
> +	if (!IS_ENABLED(CONFIG_KASAN_GENERIC))
>  		return 0;
>  
>  	return
> @@ -183,14 +183,14 @@ size_t kasan_metadata_size(struct kmem_cache *cache)
>  struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
>  					const void *object)
>  {
> -	return (void *)object + cache->kasan_info.alloc_meta_offset;
> +	return (void *)reset_tag(object) + cache->kasan_info.alloc_meta_offset;
>  }
>  
>  struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
>  				      const void *object)
>  {
>  	BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
> -	return (void *)object + cache->kasan_info.free_meta_offset;
> +	return (void *)reset_tag(object) + cache->kasan_info.free_meta_offset;
>  }
>  
>  void kasan_poison_slab(struct page *page)
> @@ -272,7 +272,8 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
>  	alloc_info = get_alloc_info(cache, object);
>  	__memset(alloc_info, 0, sizeof(*alloc_info));

Suggested edit below (assuming the line-break wasn't intentional; this
should still be within checkpatch.pl's 100 col limit):
------
-	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) ||
-			IS_ENABLED(CONFIG_KASAN_HW_TAGS))
+	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
 		object = set_tag(object,
 				assign_tag(cache, object, true, false));
 
@@ -343,8 +342,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
 	redzone_end = round_up((unsigned long)object + cache->object_size,
 				KASAN_GRANULE_SIZE);
 
-	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) ||
-			IS_ENABLED(CONFIG_KASAN_HW_TAGS))
+	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
 		tag = assign_tag(cache, object, false, keep_tag);
------

> -	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
> +	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) ||
> +			IS_ENABLED(CONFIG_KASAN_HW_TAGS))
>  		object = set_tag(object,
>  				assign_tag(cache, object, true, false));
>  
> @@ -342,10 +343,11 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
>  	redzone_end = round_up((unsigned long)object + cache->object_size,
>  				KASAN_GRANULE_SIZE);
>  
> -	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
> +	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) ||
> +			IS_ENABLED(CONFIG_KASAN_HW_TAGS))
>  		tag = assign_tag(cache, object, false, keep_tag);
>  
> -	/* Tag is ignored in set_tag without CONFIG_KASAN_SW_TAGS */
> +	/* Tag is ignored in set_tag without CONFIG_KASAN_SW/HW_TAGS */
>  	kasan_unpoison_memory(set_tag(object, tag), size);
>  	kasan_poison_memory((void *)redzone_start, redzone_end - redzone_start,
>  		KASAN_KMALLOC_REDZONE);
[...]
> diff --git a/mm/kasan/report_tags_hw.c b/mm/kasan/report_tags_hw.c
> new file mode 100644
> index 000000000000..c2f73c46279a
> --- /dev/null
> +++ b/mm/kasan/report_tags_hw.c
> @@ -0,0 +1,47 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * This file contains hardware tag-based KASAN specific error reporting code.
> + *
> + * Copyright (c) 2020 Google, Inc.
> + * Author: Andrey Konovalov <andreyknvl@google.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *

I do not think we put the "This program is ..." preamble in new files
anymore. It should be covered by SPDX tag above.

> + */
> +
> +#include <linux/kasan.h>
> +#include <linux/kernel.h>
> +#include <linux/memory.h>
> +#include <linux/mm.h>
> +#include <linux/string.h>
> +#include <linux/types.h>
[...]
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index 4888084ecdfc..ca69726adf8f 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -111,7 +111,7 @@ void kasan_unpoison_memory(const void *address, size_t size)
>  
>  		if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
>  			*shadow = tag;
> -		else
> +		else /* CONFIG_KASAN_GENERIC */
>  			*shadow = size & KASAN_GRANULE_MASK;
>  	}
>  }
> diff --git a/mm/kasan/tags_hw.c b/mm/kasan/tags_hw.c
> new file mode 100644
> index 000000000000..c93d43379e39
> --- /dev/null
> +++ b/mm/kasan/tags_hw.c
> @@ -0,0 +1,78 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * This file contains core hardware tag-based KASAN code.
> + *
> + * Copyright (c) 2020 Google, Inc.
> + * Author: Andrey Konovalov <andreyknvl@google.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *

I do not think we put the "This program is ..." preamble in new files
anymore. It should be covered by SPDX tag above.

> + */
> +
> +#include <linux/kasan.h>
> +#include <linux/kernel.h>
> +#include <linux/memory.h>
> +#include <linux/mm.h>
> +#include <linux/string.h>
> +#include <linux/types.h>
> +
> +#include "kasan.h"
> +
> +void kasan_init_tags(void)
> +{
> +	init_tags(KASAN_TAG_MAX);
> +}
> +
> +void *kasan_reset_tag(const void *addr)
> +{
> +	return reset_tag(addr);
> +}
> +

To help readability, would this edit be ok?
------
 void kasan_poison_memory(const void *address, size_t size, u8 value)
 {
-	set_mem_tag_range(reset_tag(address),
-		round_up(size, KASAN_GRANULE_SIZE), value);
+	set_mem_tag_range(reset_tag(address), round_up(size, KASAN_GRANULE_SIZE), value);
 }
 
 void kasan_unpoison_memory(const void *address, size_t size)
 {
-	set_mem_tag_range(reset_tag(address),
-		round_up(size, KASAN_GRANULE_SIZE), get_tag(address));
+	set_mem_tag_range(reset_tag(address), round_up(size, KASAN_GRANULE_SIZE), get_tag(address));
 }
------

> +void kasan_poison_memory(const void *address, size_t size, u8 value)
> +{
> +	set_mem_tag_range(reset_tag(address),
> +		round_up(size, KASAN_GRANULE_SIZE), value);
> +}
> +
> +void kasan_unpoison_memory(const void *address, size_t size)
> +{
> +	set_mem_tag_range(reset_tag(address),
> +		round_up(size, KASAN_GRANULE_SIZE), get_tag(address));
> +}
> +
> +u8 random_tag(void)
> +{
> +	return get_random_tag();
> +}
> +
> +bool check_invalid_free(void *addr)
> +{
> +	u8 ptr_tag = get_tag(addr);
> +	u8 mem_tag = get_mem_tag(addr);
> +


Why not just:
------
-	if (shadow_byte == KASAN_TAG_INVALID)
-		return true;
-	if (tag != KASAN_TAG_KERNEL && tag != shadow_byte)
-		return true;
-	return false;
+	return shadow_byte == KASAN_TAG_INVALID ||
+	       (tag != KASAN_TAG_KERNEL && tag != shadow_byte);
 }
------

> +	if (mem_tag == KASAN_TAG_INVALID)
> +		return true;
> +	if (ptr_tag != KASAN_TAG_KERNEL && ptr_tag != mem_tag)
> +		return true;
> +	return false;
> +}
> +

Thanks,
-- Marco

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel