Re: [PATCH] powerpc: Avoid integer overflow in page_is_ram()

Kumar Gala
2008-09-15T22:44:30Z

On Sep 15, 2008, at 3:43 PM, Roland Dreier wrote:

> Commit 8b150478 ("ppc: make phys_mem_access_prot() work with pfns
> instead of addresses") fixed page_is_ram() in arch/ppc to avoid
> overflow
> for addresses above 4G on 32-bit kernels. However arch/powerpc's
> page_is_ram() is missing the same fix -- it computes a physical
> address
> by doing pfn << PAGE_SHIFT, which overflows if pfn corresponds to a
> page
> above 4G.
>
> In particular this causes pages above 4G to be mapped with the wrong
> caching attribute; for example many ppc440-based SoCs have PCI space
> above 4G, and mmap()ing MMIO space may end up with a mapping that has
> caching enabled.
>
> Fix this by working with the pfn and avoiding the conversion to
> physical address that causes the overflow. This patch compares the
> pfn to max_pfn, which is a semantic change from the old code -- that
> code compared the physical address to high_memory, which corresponds
> to max_low_pfn. However, I think that was is another bug, since
> highmem pages are still RAM.
>
> Reported-by: vb <vb@vsbe.com>
> Signed-off-by: Roland Dreier <rolandd@cisco.com>
> Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>
> ---
> Paul, didn't see this in your list... please add for 2.6.28.
>
> arch/powerpc/mm/mem.c | 5 ++---
> 1 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 1c93c25..98d7bf9 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -75,11 +75,10 @@ static inline pte_t *virt_to_kpte(unsigned long
> vaddr)
>
> int page_is_ram(unsigned long pfn)
> {
> - unsigned long paddr = (pfn << PAGE_SHIFT);
> -
> #ifndef CONFIG_PPC64 /* XXX for now */
> - return paddr < __pa(high_memory);
> + return pfn < max_pfn;
> #else
> + unsigned long paddr = (pfn << PAGE_SHIFT);

seems like this could be a phys_addr_t

>
> int i;
> for (i=0; i < lmb.memory.cnt; i++) {
> unsigned long base;

- k