Re: [PATCH] intel-iommu: Fix use after release during device attach

Sheng Yang
2010-11-02T08:00:43Z

On Tuesday 02 November 2010 15:31:22 Sheng Yang wrote:
> On Tuesday 02 November 2010 15:05:51 Jan Kiszka wrote:
> > From: Jan Kiszka <jan.kiszka@siemens.com>
> >
> > Obtail the new pgd pointer before releasing the page containing this
> > value.
> >
> > Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> > ---
> >
> > Who is taking care of this? The kvm tree?
> >
> > drivers/pci/intel-iommu.c | 2 +-
> > 1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> > index 4789f8e..35463dd 100644
> > --- a/drivers/pci/intel-iommu.c
> > +++ b/drivers/pci/intel-iommu.c
> > @@ -3627,9 +3627,9 @@ static int intel_iommu_attach_device(struct
> > iommu_domain *domain,
> >
> > pte = dmar_domain->pgd;
> > if (dma_pte_present(pte)) {
> >
> > - free_pgtable_page(dmar_domain->pgd);
> >
> > dmar_domain->pgd = (struct dma_pte *)
> >
> > phys_to_virt(dma_pte_addr(pte));
> >
> > + free_pgtable_page(pte);
> >
> > }
> > dmar_domain->agaw--;
> >
> > }
>
> Reviewed-by: Sheng Yang <sheng@linux.intel.com>
>
> CC iommu mailing list and David.
>
> OK, Jan, I got your meaning now. And it's not the exactly swap. :)
>
> I think the old code is safe, seems it's broken(exposed) by:
>
> commit 1a8bd481bfba30515b54368d90a915db3faf302f
> Author: David Woodhouse <David.Woodhouse@intel.com>
> Date: Tue Aug 10 01:38:53 2010 +0100
>
> intel-iommu: Fix 32-bit build warning with __cmpxchg()

In fact this one shouldn't affect the result. Wrong guess...

--
regards
Yang, Sheng

>
> drivers/pci/intel-iommu.c: In function 'dma_pte_addr':
> drivers/pci/intel-iommu.c:239: warning: passing argument 1 of
> '__cmpxchg64' from incompatible pointer typ
>
> It seems that __cmpxchg64() now cares about the type of its pointer
> argument, so give it a (uint64_t *) instead of a pointer to a structure
> which contains only that.
>
> Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
>
> diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> index c9171be..603cdc0 100644
> --- a/drivers/pci/intel-iommu.c
> +++ b/drivers/pci/intel-iommu.c
> @@ -236,7 +236,7 @@ static inline u64 dma_pte_addr(struct dma_pte *pte)
> return pte->val & VTD_PAGE_MASK;
> #else
> /* Must have a full atomic 64-bit read */
> - return __cmpxchg64(pte, 0ULL, 0ULL) & VTD_PAGE_MASK;
> + return __cmpxchg64(&pte->val, 0ULL, 0ULL) & VTD_PAGE_MASK;
> #endif
> }
>
> Seems here is the only affected code?
>
> --
> regards
> Yang, Sheng
> --
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