Re: [Xen-devel] [PATCH for-4.8] libxc: fix unmap of ACPI guest memory region

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On Tue, Nov 08, 2016 at 12:19:06PM -0500, Boris Ostrovsky wrote:
> 
> 
> On 11/08/2016 11:22 AM, Roger Pau Monne wrote:
> > Commit fac7f7 changed the value of ptr so that it points to the right memory
> > area, taking the page offset into account, but failed to remove this when
> > doing the unmap, which caused the region to not be unmapped. Fix this by not
> > modifying ptr and instead adding the page offset directly in the memcpy
> > call.
> > 
> > Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > Cc: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> > ---
> >  tools/libxc/xc_dom_core.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/tools/libxc/xc_dom_core.c b/tools/libxc/xc_dom_core.c
> > index ad819dd..36cd3c8 100644
> > --- a/tools/libxc/xc_dom_core.c
> > +++ b/tools/libxc/xc_dom_core.c
> > @@ -1119,10 +1119,9 @@ static int xc_dom_load_acpi(struct xc_dom_image *dom)
> >              goto err;
> >          }
> > 
> > -        ptr = (uint8_t *)ptr +
> > -              (dom->acpi_modules[i].guest_addr_out & ~XC_PAGE_MASK);
> > -
> > -        memcpy(ptr, dom->acpi_modules[i].data, 
> > dom->acpi_modules[i].length);
> > +        memcpy((uint8_t *)ptr +
> > +               (dom->acpi_modules[i].guest_addr_out & ~XC_PAGE_MASK),
> > +               dom->acpi_modules[i].data, dom->acpi_modules[i].length);
> >          munmap(ptr, XC_PAGE_SIZE * num_pages);
> > 
> >          free(extents);
> > 
> 
> 
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> 
> (Although I don't think this would cause memory not to be unmapped: per
> Linux man page "All pages containing a part of the indicated range are
> unmapped ..." and ptr is offset from its original value by a fraction of a
> page.)

Linux man page states:

"The implementation shall require that addr be a multiple of the page size 
{PAGESIZE}."

And on FreeBSD:

"The munmap() system call will fail if: The addr argument was not page 
aligned, [...]"

Roger.

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