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

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Date:	Tue, 2 Nov 2010 15:31:22 +0800
From:	Sheng Yang <sheng@...ux.intel.com>
To:	Jan Kiszka <jan.kiszka@....de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	iommu@...ts.linux-foundation.org,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] intel-iommu: Fix use after release during device attach

On Tuesday 02 November 2010 15:05:51 Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@...mens.com>
> 
> Obtail the new pgd pointer before releasing the page containing this
> value.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.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@...ux.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@...el.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@...el.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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