linux-kernel - Re: [PATCH] x86: add phys addr validity check for /dev/mem mmap

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Message-ID: <515B2802.1050405@zytor.com>
Date:	Tue, 02 Apr 2013 11:48:34 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Frantisek Hrbata <fhrbata@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	oleg@...hat.com, kamaleshb@...ibm.com, hechjie@...ibm.com
Subject: Re: [PATCH] x86: add phys addr validity check for /dev/mem mmap

On 04/02/2013 05:28 AM, Frantisek Hrbata wrote:
> 
> diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> index d8e8eef..39607c6 100644
> --- a/arch/x86/include/asm/io.h
> +++ b/arch/x86/include/asm/io.h
> @@ -242,6 +242,10 @@ static inline void flush_write_buffers(void)
>  #endif
>  }
>  
> +#define ARCH_HAS_VALID_PHYS_ADDR_RANGE
> +extern int valid_phys_addr_range(phys_addr_t addr, size_t count);
> +extern int valid_mmap_phys_addr_range(unsigned long pfn, size_t count);
> +
>  #endif /* __KERNEL__ */
>  
>  extern void native_io_delay(void);
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 845df68..92ec31c 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -31,6 +31,8 @@
>  #include <linux/sched.h>
>  #include <asm/elf.h>
>  
> +#include "physaddr.h"
> +
>  struct __read_mostly va_alignment va_align = {
>  	.flags = -1,
>  };
> @@ -122,3 +124,14 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
>  		mm->unmap_area = arch_unmap_area_topdown;
>  	}
>  }
> +
> +int valid_phys_addr_range(phys_addr_t addr, size_t count)
> +{
> +	return addr + count <= __pa(high_memory);
> +}
> +
> +int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
> +{
> +	resource_size_t addr = (pfn << PAGE_SHIFT) + count;
> +	return phys_addr_valid(addr);
> +}
> 

Good initiative, but I think the implementation is worong.  I suspect we
should use the number of physical address bits supported rather than
high_memory, since it is common and legal to use /dev/mem to access I/O
resources that are beyond the last byte of RAM.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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