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

[David Marchand <david.marchand@redhat.com>]

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;

-- 
David Marchand