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

Sheng Yang
2010-11-02T07:31:25Z

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()

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