Re: [PATCH v9 4/4] libs/guest: use Valgrind to detect various buffer overflows

On Wed, 15 Jul 2026 at 14:38, Andrew Cooper <[email protected]> wrote:
>
> On 13/07/2026 9:48 pm, Frediano Ziglio wrote:
> > diff --git a/tools/libs/guest/xg_sr_common.h b/tools/libs/guest/xg_sr_common.h
> > index c07c6db59e..d3fc7f363e 100644
> > --- a/tools/libs/guest/xg_sr_common.h
> > +++ b/tools/libs/guest/xg_sr_common.h
> > @@ -245,13 +245,21 @@ struct xc_sr_context
> >              xc_hypercall_buffer_t dirty_bitmap_hbuf;
> >              struct xc_sr_context_save_buffers
> >              {
> > +                MEM_NOACCESS_BUFFER(na0, 16);
> >                  xen_pfn_t batch_pfns[MAX_BATCH_SIZE];
> > +                MEM_NOACCESS_BUFFER(na1, 16);
> >                  xen_pfn_t mfns[MAX_BATCH_SIZE];
> > +                MEM_NOACCESS_BUFFER(na2, 16);
> >                  xen_pfn_t types[MAX_BATCH_SIZE];
> > +                MEM_NOACCESS_BUFFER(na3, 16);
> >                  void *local_pages[MAX_BATCH_SIZE];
> > +                MEM_NOACCESS_BUFFER(na4, 16);
> >                  struct iovec iov[MAX_BATCH_SIZE + 2]; /* Headers + data. */
> > +                MEM_NOACCESS_BUFFER(na5, 16);
> >                  uint64_t rec_pfns[MAX_BATCH_SIZE];
> > +                MEM_NOACCESS_BUFFER(na6, 16);
> >                  int errors[MAX_BATCH_SIZE];
> > +                MEM_NOACCESS_BUFFER(na7, 16);
>
> If you're going to do this, use 64 not 16, and put iov[] at the end.  It
> is good practice to misalign large buffers by one cacheline, not that I
> suspect the access pattern in this algorithm is relevant.
>

Easily doable. Why put "iov" at the end?

> But, I'm not sure of the utility of doing this.  By removing the dynamic
> allocations you also prevent ASAN from working.
>

It can be extended to ASAN using "sanitizer/asan_interface.h",
specifically "ASAN_POISON_MEMORY_REGION" macro.

> We either care about them all (and keep the dynamic allocations), or
> don't care, and get rid of it all.  This half-way-house serves no good
> purpose.
>
> ~Andrew

Why is a half-way-house ?

Frediano