[PATCH] Revert "mm/usercopy: Drop extra is_vmalloc_or_module() check"

[Kefeng Wang]

On 2021/12/24 21:18, Christophe Leroy wrote:
>
> Le 24/12/2021 à 08:06, Kefeng Wang a écrit :
>> On 2021/12/24 14:01, Christophe Leroy wrote:
>>> Le 23/12/2021 à 11:21, Kefeng Wang a écrit :
>>>> This reverts commit 517e1fbeb65f5eade8d14f46ac365db6c75aea9b.
>>>>
>>>>      usercopy: Kernel memory exposure attempt detected from SLUB
>>>> object not in SLUB page?! (offset 0, size 1048)!
>>>>      kernel BUG at mm/usercopy.c:99
>>>>      ...
>>>>      usercopy_abort+0x64/0xa0 (unreliable)
>>>>      __check_heap_object+0x168/0x190
>>>>      __check_object_size+0x1a0/0x200
>>>>      dev_ethtool+0x2494/0x2b20
>>>>      dev_ioctl+0x5d0/0x770
>>>>      sock_do_ioctl+0xf0/0x1d0
>>>>      sock_ioctl+0x3ec/0x5a0
>>>>      __se_sys_ioctl+0xf0/0x160
>>>>      system_call_exception+0xfc/0x1f0
>>>>      system_call_common+0xf8/0x200
>>>>
>>>> When run ethtool eth0, the BUG occurred, the code shows below,
>>>>
>>>>      data = vzalloc(array_size(gstrings.len, ETH_GSTRING_LEN));
>>>>      copy_to_user(useraddr, data, gstrings.len * ETH_GSTRING_LEN))
>>>>
>>>> The data is alloced by vmalloc(),  virt_addr_valid(ptr) will return true
>>>> on PowerPC64, which leads to the panic, add back the
>>>> is_vmalloc_or_module()
>>>> check to fix it.
>>> Is it expected that virt_addr_valid() returns true on PPC64 for
>>> vmalloc'ed memory ? If that's the case it also means that
>>> CONFIG_DEBUG_VIRTUAL won't work as expected either.
>> Our product reports this bug to me, after let them do some test,
>>
>> I found virt_addr_valid return true for vmalloc'ed memory on their board.
>>
>> I think DEBUG_VIRTUAL could not be work well too, but I can't test it.
>>
>>> If it is unexpected, I think you should fix PPC64 instead of adding this
>>> hack back. Maybe the ARM64 fix can be used as a starting point, see
>>> commit 68dd8ef32162 ("arm64: memory: Fix virt_addr_valid() using
>>> __is_lm_address()")
>> Yes， I check the history,  fix virt_addr_valid() on PowerPC is what I
>> firstly want to do,
>>
>> but I am not familiar with PPC, and also HARDENED_USERCOPY on other's
>> ARCHs could
>>
>> has this issue too, so I add the workaround back.
>>
>>
>> 1) PPC maintainer/expert, any suggestion ?
>>
>> 2) Maybe we could add some check to WARN this scenario.
>>
>> --- a/mm/usercopy.c
>> +++ b/mm/usercopy.c
>> @@ -229,6 +229,8 @@ static inline void check_heap_object(const void
>> *ptr, unsigned long n,
>>           if (!virt_addr_valid(ptr))
>>                   return;
>>
>> +       WARN_ON_ONCE(is_vmalloc_or_module_addr(ptr));

>>
>>> In the meantime, can you provide more information on your config,
>>> especially which memory model is used ?
>> Some useful configs,
>>
>> CONFIG_PPC64=y
>> CONFIG_PPC_BOOK3E_64=y
>> CONFIG_E5500_CPU=y
>> CONFIG_TARGET_CPU_BOOL=y
>> CONFIG_PPC_BOOK3E=y
>> CONFIG_E500=y
>> CONFIG_PPC_E500MC=y
>> CONFIG_PPC_FPU=y
>> CONFIG_FSL_EMB_PERFMON=y
>> CONFIG_FSL_EMB_PERF_EVENT=y
>> CONFIG_FSL_EMB_PERF_EVENT_E500=y
>> CONFIG_BOOKE=y
>> CONFIG_PPC_FSL_BOOK3E=y
>> CONFIG_PTE_64BIT=y
>> CONFIG_PHYS_64BIT=y
>> CONFIG_PPC_MMU_NOHASH=y
>> CONFIG_PPC_BOOK3E_MMU=y
>> CONFIG_SELECT_MEMORY_MODEL=y
>> CONFIG_FLATMEM_MANUAL=y
>> CONFIG_FLATMEM=y
>> CONFIG_FLAT_NODE_MEM_MAP=y
>> CONFIG_SPARSEMEM_VMEMMAP_ENABLE=y
>>
> OK so it is PPC64 book3e and with flatmem.
>
> The problem is virt_to_pfn() which uses __pa()
>
> __pa(x) on PPC64 is (x) & 0x0fffffffffffffffUL
>
> And on book3e/64 we have
>
> VMALLOC_START = KERN_VIRT_START = ASM_CONST(0x8000000000000000)
>
>
> It means that __pa() will return a valid PFN for VMALLOCed addresses.
>
>
> So an additional check is required in virt_addr_valid(), maybe check
> that (kaddr & PAGE_OFFSET) == PAGE_OFFSET
>
> Can you try that ?
>
> #define virt_addr_valid(kaddr)	((kaddr & PAGE_OFFSET) == PAGE_OFFSET &&
> pfn_valid(virt_to_pfn(kaddr)))

I got this commit,

commit 4dd7554a6456d124c85e0a4ad156625b71390b5c

Author: Nicholas Piggin <npiggin at gmail.com>
Date:   Wed Jul 24 18:46:37 2019 +1000

     powerpc/64: Add VIRTUAL_BUG_ON checks for __va and __pa addresses

     Ensure __va is given a physical address below PAGE_OFFSET, and __pa is
     given a virtual address above PAGE_OFFSET.

It has check the PAGE_OFFSET in __pa,  will test it and resend the 
patch(with above warning changes).

Thanks.

>
>
> Thanks
> Christophe