Re: [RFC/PATCH RESEND -next 08/21] mm: page_alloc: add kasan hooks on alloc and free pathes

[Joonsoo Kim]

On Wed, Jul 09, 2014 at 03:30:02PM +0400, Andrey Ryabinin wrote:
> Add kernel address sanitizer hooks to mark allocated page's addresses
> as accessible in corresponding shadow region.
> Mark freed pages as unaccessible.
> 
> Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
> ---
>  include/linux/kasan.h |  6 ++++++
>  mm/Makefile           |  2 ++
>  mm/kasan/kasan.c      | 18 ++++++++++++++++++
>  mm/kasan/kasan.h      |  1 +
>  mm/kasan/report.c     |  7 +++++++
>  mm/page_alloc.c       |  4 ++++
>  6 files changed, 38 insertions(+)
> 
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 7efc3eb..4adc0a1 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -17,6 +17,9 @@ void kasan_disable_local(void);
>  void kasan_alloc_shadow(void);
>  void kasan_init_shadow(void);
>  
> +void kasan_alloc_pages(struct page *page, unsigned int order);
> +void kasan_free_pages(struct page *page, unsigned int order);
> +
>  #else /* CONFIG_KASAN */
>  
>  static inline void unpoison_shadow(const void *address, size_t size) {}
> @@ -28,6 +31,9 @@ static inline void kasan_disable_local(void) {}
>  static inline void kasan_init_shadow(void) {}
>  static inline void kasan_alloc_shadow(void) {}
>  
> +static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
> +static inline void kasan_free_pages(struct page *page, unsigned int order) {}
> +
>  #endif /* CONFIG_KASAN */
>  
>  #endif /* LINUX_KASAN_H */
> diff --git a/mm/Makefile b/mm/Makefile
> index dbe9a22..6a9c3f8 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -2,6 +2,8 @@
>  # Makefile for the linux memory manager.
>  #
>  
> +KASAN_SANITIZE_page_alloc.o := n
> +
>  mmu-y			:= nommu.o
>  mmu-$(CONFIG_MMU)	:= gup.o highmem.o madvise.o memory.o mincore.o \
>  			   mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
> index e2cd345..109478e 100644
> --- a/mm/kasan/kasan.c
> +++ b/mm/kasan/kasan.c
> @@ -177,6 +177,24 @@ void __init kasan_init_shadow(void)
>  	}
>  }
>  
> +void kasan_alloc_pages(struct page *page, unsigned int order)
> +{
> +	if (unlikely(!kasan_initialized))
> +		return;
> +
> +	if (likely(page && !PageHighMem(page)))
> +		unpoison_shadow(page_address(page), PAGE_SIZE << order);
> +}
> +
> +void kasan_free_pages(struct page *page, unsigned int order)
> +{
> +	if (unlikely(!kasan_initialized))
> +		return;
> +
> +	if (likely(!PageHighMem(page)))
> +		poison_shadow(page_address(page), PAGE_SIZE << order, KASAN_FREE_PAGE);
> +}
> +
>  void *kasan_memcpy(void *dst, const void *src, size_t len)
>  {
>  	if (unlikely(len == 0))
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 711ae4f..be9597e 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -5,6 +5,7 @@
>  #define KASAN_SHADOW_SCALE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT)
>  #define KASAN_SHADOW_MASK       (KASAN_SHADOW_SCALE_SIZE - 1)
>  
> +#define KASAN_FREE_PAGE         0xFF  /* page was freed */
>  #define KASAN_SHADOW_GAP        0xF9  /* address belongs to shadow memory */
>  
>  struct access_info {
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 2430e05..6ef9e57 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -46,6 +46,9 @@ static void print_error_description(struct access_info *info)
>  	case 0 ... KASAN_SHADOW_SCALE_SIZE - 1:
>  		bug_type = "buffer overflow";
>  		break;
> +	case KASAN_FREE_PAGE:
> +		bug_type = "use after free";
> +		break;
>  	case KASAN_SHADOW_GAP:
>  		bug_type = "wild memory access";
>  		break;
> @@ -67,6 +70,10 @@ static void print_address_description(struct access_info *info)
>  	page = virt_to_page(info->access_addr);
>  
>  	switch (shadow_val) {
> +	case KASAN_FREE_PAGE:
> +		dump_page(page, "kasan error");
> +		dump_stack();
> +		break;
>  	case KASAN_SHADOW_GAP:
>  		pr_err("No metainfo is available for this access.\n");
>  		dump_stack();
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8c9eeec..67833d1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -61,6 +61,7 @@
>  #include <linux/page-debug-flags.h>
>  #include <linux/hugetlb.h>
>  #include <linux/sched/rt.h>
> +#include <linux/kasan.h>
>  
>  #include <asm/sections.h>
>  #include <asm/tlbflush.h>
> @@ -747,6 +748,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
>  
>  	trace_mm_page_free(page, order);
>  	kmemcheck_free_shadow(page, order);
> +	kasan_free_pages(page, order);
>  
>  	if (PageAnon(page))
>  		page->mapping = NULL;
> @@ -2807,6 +2809,7 @@ out:
>  	if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
>  		goto retry_cpuset;
>  
> +	kasan_alloc_pages(page, order);
>  	return page;
>  }
>  EXPORT_SYMBOL(__alloc_pages_nodemask);
> @@ -6415,6 +6418,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>  	if (end != outer_end)
>  		free_contig_range(end, outer_end - end);
>  
> +	kasan_alloc_pages(pfn_to_page(start), end - start);
>  done:
>  	undo_isolate_page_range(pfn_max_align_down(start),
>  				pfn_max_align_up(end), migratetype);

Hello,

I don't think that this is right place for this hook.

There is a function, __isolate_free_pages(), which steals buddy pages
from page allocator. So you should put this hook onto that function.

alloc_contig_range() uses that function through below call path, so
adding hook on it solves your issue here.

alloc_contig_range() -> isolate_freepages_range() ->
isolate_freepages_block() -> split_free_page -> __isolate_free_page()

And, this also solves marking issue on compaction logic, since
compaction also steal buddy pages from page allocator through
isolate_freepages() -> isolate_freepages_block() -> split_free_page()
-> __isolate_free_page().

Thanks.
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