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

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Date:	Fri, 26 Apr 2013 13:21:28 +0800
From:	Will Huck <will.huckk@...il.com>
To:	Frantisek Hrbata <fhrbata@...hat.com>, hpa@...or.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

Hi Peter,
On 04/02/2013 08:28 PM, Frantisek Hrbata wrote:
> When CR4.PAE is set, the 64b PTE's are used(ARCH_PHYS_ADDR_T_64BIT is set for
> X86_64 || X86_PAE). According to [1] Chapter 4 Paging, some higher bits in 64b
> PTE are reserved and have to be set to zero. For example, for IA-32e and 4KB
> page [1] 4.5 IA-32e Paging: Table 4-19, bits 51-M(MAXPHYADDR) are reserved. So
> for a CPU with e.g. 48bit phys addr width, bits 51-48 have to be zero. If one of
> the reserved bits is set, [1] 4.7 Page-Fault Exceptions, the #PF is generated
> with RSVD error code.
>
> <quote>
> RSVD flag (bit 3).
> This flag is 1 if there is no valid translation for the linear address because a
> reserved bit was set in one of the paging-structure entries used to translate
> that address. (Because reserved bits are not checked in a paging-structure entry
> whose P flag is 0, bit 3 of the error code can be set only if bit 0 is also
> set.)
> </quote>
>
> In mmap_mem() the first check is valid_mmap_phys_addr_range(), but it always
> returns 1 on x86. So it's possible to use any pgoff we want and to set the PTE's
> reserved bits in remap_pfn_range(). Meaning there is a possibility to use mmap

In this case, remap_pfn_range() setup the map and reserved bits for mmio 
memory, so the mmio memory is already populated, why trigger #PF?

> on /dev/mem and cause system panic. It's probably not that serious, because
> access to /dev/mem is limited and the system has to have panic_on_oops set, but
> still I think we should check this and return error.
>
> This patch adds check for x86 when ARCH_PHYS_ADDR_T_64BIT is set, the same way
> as it is already done in e.g. ioremap. With this fix mmap returns -EINVAL if the
> requested phys addr is bigger then the supported phys addr width.
>
> [1] Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3A
>
> Signed-off-by: Frantisek Hrbata <fhrbata@...hat.com>
> ---
>   arch/x86/include/asm/io.h |  4 ++++
>   arch/x86/mm/mmap.c        | 13 +++++++++++++
>   2 files changed, 17 insertions(+)
>
> 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);
> +}

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