Subject: Re: [PATCH V2] powerpc: Fail remap_4k_pfn() if PFN doesn't fit inside PTE

From: Brian W Hart <[email-masked]>
Date: Thu, 10 Jul 2014 08:59:52 -0500

On Thu, Jul 10, 2014 at 02:12:19PM +0530, Madhusudanan Kandasamy wrote:
> V2 : Rewritten to avoid helper function as suggested by Stephen Rothwell.
> remap_4k_pfn() silently truncates upper bits of input 4K PFN if
> it cannot be contained in PTE. This leads invalid memory mapping
> and could result in a system crash when the memory is accessed.
> This patch fails remap_4k_pfn() and returns -EINVAL if the input
> 4K PFN cannot be contained in PTE.
> 
> Signed-off-by: Madhusudanan Kandasamy <[email-masked]>
> ---
>  arch/powerpc/include/asm/pte-hash64-64k.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/pte-hash64-64k.h b/arch/powerpc/include/asm/pte-hash64-64k.h
> index d836d94..b5178e4 100644
> --- a/arch/powerpc/include/asm/pte-hash64-64k.h
> +++ b/arch/powerpc/include/asm/pte-hash64-64k.h
> @@ -75,7 +75,8 @@
>  	(((pte) & _PAGE_COMBO)? MMU_PAGE_4K: MMU_PAGE_64K)
> 
>  #define remap_4k_pfn(vma, addr, pfn, prot)				\
> -	remap_pfn_range((vma), (addr), (pfn), PAGE_SIZE,		\
> +	WARN_ON((pfn >= (1UL << (64 - PTE_RPN_SHIFT)))) ? -EINVAL :	\
> +		remap_pfn_range((vma), (addr), (pfn), PAGE_SIZE,	\
>  			__pgprot(pgprot_val((prot)) | _PAGE_4K_PFN))
> 
>  #endif	/* __ASSEMBLY__ */
> -- 
> 2.0.1

Chatted with Madhu.  He'll send a new version that adds some
parentheses to protect 'pfn' inside the macro and the entire macro
against use cases like:

    !remap_4k_pfn(...)

brian