Re: [PATCH 2/3] mem: fix ASan shadow for remapped memory segments

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 21-Apr-22 10:37 AM, David Marchand wrote:
> On Wed, Apr 20, 2022 at 4:47 PM Burakov, Anatoly
> <anatoly.burakov@intel.com> wrote:
>>
>> On 15-Apr-22 6:31 PM, David Marchand wrote:
>>> When releasing some memory, the allocator can choose to return some
>>> pages to the OS. At the same time, this memory was poisoned in ASAn
>>> shadow. Doing the latter made it impossible to remap this same page
>>> later.
>>> On the other hand, without this poison, the OS would pagefault in any
>>> case for this page.
>>>
>>> Remove the poisoning for unmapped pages.
>>>
>>> Bugzilla ID: 994
>>> Fixes: 6cc51b1293ce ("mem: instrument allocator for ASan")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: David Marchand <david.marchand@redhat.com>
>>> ---
>>>    lib/eal/common/malloc_elem.h |  4 ++++
>>>    lib/eal/common/malloc_heap.c | 12 +++++++++++-
>>>    2 files changed, 15 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/lib/eal/common/malloc_elem.h b/lib/eal/common/malloc_elem.h
>>> index 228f178418..b859003722 100644
>>> --- a/lib/eal/common/malloc_elem.h
>>> +++ b/lib/eal/common/malloc_elem.h
>>> @@ -272,6 +272,10 @@ old_malloc_size(struct malloc_elem *elem)
>>>
>>>    #else /* !RTE_MALLOC_ASAN */
>>>
>>> +static inline void
>>> +asan_set_zone(void *ptr __rte_unused, size_t len __rte_unused,
>>> +     uint32_t val __rte_unused) { }
>>> +
>>>    static inline void
>>>    asan_set_freezone(void *ptr __rte_unused, size_t size __rte_unused) { }
>>>
>>> diff --git a/lib/eal/common/malloc_heap.c b/lib/eal/common/malloc_heap.c
>>> index 6c572b6f2c..5913d9f862 100644
>>> --- a/lib/eal/common/malloc_heap.c
>>> +++ b/lib/eal/common/malloc_heap.c
>>> @@ -860,6 +860,7 @@ malloc_heap_free(struct malloc_elem *elem)
>>>        size_t len, aligned_len, page_sz;
>>>        struct rte_memseg_list *msl;
>>>        unsigned int i, n_segs, before_space, after_space;
>>> +     bool unmapped_pages = false;
>>>        int ret;
>>>        const struct internal_config *internal_conf =
>>>                eal_get_internal_configuration();
>>> @@ -999,6 +1000,13 @@ malloc_heap_free(struct malloc_elem *elem)
>>>
>>>                /* don't care if any of this fails */
>>>                malloc_heap_free_pages(aligned_start, aligned_len);
>>> +             /*
>>> +              * Clear any poisoning in ASan for the associated pages so that
>>> +              * next time EAL maps those pages, the allocator can access
>>> +              * them.
>>> +              */
>>> +             asan_set_zone(aligned_start, aligned_len, 0x00);
>>> +             unmapped_pages = true;
>>>
>>>                request_sync();
>>>        } else {
>>> @@ -1032,7 +1040,9 @@ malloc_heap_free(struct malloc_elem *elem)
>>>
>>>        rte_mcfg_mem_write_unlock();
>>>    free_unlock:
>>> -     asan_set_freezone(asan_ptr, asan_data_len);
>>> +     /* Poison memory range if belonging to some still mapped pages. */
>>> +     if (!unmapped_pages)
>>> +             asan_set_freezone(asan_ptr, asan_data_len);
>>>
>>>        rte_spinlock_unlock(&(heap->lock));
>>>        return ret;
>>
>> I suspect the patch should be a little more complicated than that. When
>> we unmap pages, we don't necessarily unmap the entire malloc element, it
>> could be that we have a freed allocation like so:
>>
>> | malloc header | free space | unmapped space | free space | next malloc
>> header |
>>
>> So, i think the freezone should be set from asan_ptr till aligned_start,
>> and then from (aligned_start + aligned_len) till (asan_ptr +
>> asan_data_len). Does that make sense?
> 
> (btw, I get a bounce for Zhihong mail address, is he not working at
> Intel anymore?)
> 
> To be honest, I don't understand if we can get to this situation :-)
> (especially the free space after the unmapped region).
> But I guess you mean something like (on top of current patch):
> 
> @@ -1040,9 +1040,25 @@ malloc_heap_free(struct malloc_elem *elem)
> 
>          rte_mcfg_mem_write_unlock();
>   free_unlock:
> -       /* Poison memory range if belonging to some still mapped pages. */
> -       if (!unmapped_pages)
> +       if (!unmapped_pages) {
>                  asan_set_freezone(asan_ptr, asan_data_len);
> +       } else {
> +               /*
> +                * We may be in a situation where we unmapped pages like this:
> +                * malloc header | free space | unmapped space | free
> space | malloc header
> +                */
> +               void *free1_start = asan_ptr;
> +               void *free1_end = aligned_start;
> +               void *free2_start = RTE_PTR_ADD(aligned_start, aligned_len);
> +               void *free2_end = RTE_PTR_ADD(asan_ptr, asan_data_len);
> +
> +               if (free1_start < free1_end)
> +                       asan_set_freezone(free1_start,
> +                               RTE_PTR_DIFF(free1_end, free1_start));
> +               if (free2_start < free2_end)
> +                       asan_set_freezone(free2_start,
> +                               RTE_PTR_DIFF(free2_end, free2_start));
> +       }
> 
>          rte_spinlock_unlock(&(heap->lock));
>          return ret;
> 

Something like that, yes. I will have to think through this a bit more, 
especially in light of your func_reentrancy splat :)

-- 
Thanks,
Anatoly