Re: [PATCH 1/1] amd/iommu: Fix infinite loop when handling IO_PAGE_FAULT event

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 29/12/2013 09:35, suravee.suthikulpanit@amd.com wrote:
> From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
>
> Certain AMD systems could have upto 0x1000 ivrs_bdf_entries.
> However, the loop variable (bdf) is declared as u16 which causes
> inifinite loop when parsing IOMMU event log with IO_PAGE_FAULT event.
> This patch changes the variable to u32 instead.

Do you perhaps mean that there could be 0x10000 ivrs_bdf_entries? 
Otherwise I cant see how an infinite loop is possible.

On the other hand, assuming that the infinite loop is possible, it is
also vulnerable in register_exclusion_range_for_{all,iommu}_devices(),
which also have similar for loops with a u16 bdf.

Even if you do promote to a u32, the get_dma_requestor_id() call now
truncates a u32 to a u16, so can now return the wrong device.

Beyond that, there is already quite a mix of u32, int and u16's for
various bdf values across the this area of the code, with plenty of
truncation issues at a glance.

~Andrew

>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
> NOTE: I found this issue on both stable-4.3 and master branches.
> Do you think we can also back port this change to 4.3 as well?
>
>  xen/drivers/passthrough/amd/iommu_init.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/xen/drivers/passthrough/amd/iommu_init.c b/xen/drivers/passthrough/amd/iommu_init.c
> index b431d16..b96a4af 100644
> --- a/xen/drivers/passthrough/amd/iommu_init.c
> +++ b/xen/drivers/passthrough/amd/iommu_init.c
> @@ -524,8 +524,8 @@ static hw_irq_controller iommu_maskable_msi_type = {
>  
>  static void parse_event_log_entry(struct amd_iommu *iommu, u32 entry[])
>  {
> -    u16 domain_id, device_id, bdf, flags;
> -    u32 code;
> +    u16 domain_id, device_id, flags;
> +    u32 code, bdf;
>      u64 *addr;
>      int count = 0;
>      static const char *const event_str[] = {