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

[Andrey Ryabinin]

On 07/15/14 09:52, Joonsoo Kim wrote:
> 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.
>

I'm also made a stupid mistake here. kasan_alloc_pages() expects page order here,
not count of pages.

> 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().
> 
Yep, I've seen some false positives when compaction
was enabled and just yesterday I've fixed it as your suggested.

I'm also going to move kasan_alloc_pages hook from alloc_pages_nodemask()
to prep_new_page. I think this is more right place for such hook and will
make possible to enable instrumentation for page_alloc.c

Thanks
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