Re: [PATCH v2] powerpc/mm: Use is_vmalloc_addr to validate addr

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 04/07/2022 à 09:45, Aneesh Kumar K V a écrit :
> On 7/4/22 12:43 PM, Christophe Leroy wrote:
>>
>>
>> Le 04/07/2022 à 08:39, Aneesh Kumar K.V a écrit :
>>> Instead of high_memory use is_vmalloc_addr to validate that the address is
>>> not in the vmalloc range.
>>
>>
>> Do we really need even more extra checks, and a function that is not
>> inlined anymore ?
>>
>> virt_addr_valid() used to be pretty simple. Some extra tests were added
>> by commit ffa0b64e3be5 ("powerpc: Fix virt_addr_valid() for 64-bit
>> Book3E & 32-bit") in order to work around some corner cases, and the
>> commit message say they are temporary.
>>
>> virt_addr_valid() is there to check that an address is a valid linear
>> mapping, not that an address IS NOT a vmalloc address. What will happen
>> with your check if you pass an address that is from an ioremap done
>> prior to the start of the vmalloc system ?
>>
> 
> I was expecting the io range to be handled by pfn_valid(). IS there a memory layout
> ascii diagram of book3e/64 like asm/book3s/64/radix.h:51 ? My goal with the
> change was to make it more explicit what is it being validated.


Yes you are right it should be handled by pfn_valid(), just like the 
entire VMALLOC range indeed. But on PPC32 a valid pfn might hit above 
vmalloc space as well.

You can find the new layout here : 
https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?id=c7b9ed7c34a9f5dbf8222d63e3e313cef9f3150b

The only problem we have with pfn_valid() is for PPC32 because 
pfn_valid() also include highmem memory. That's the reason why we need 
to check that the address is below high_memory in addition.

For everything else, pfn_valid() should be enough.

For PPC64, we may want to add a verification that we are in the 0xc.... 
range, because of the way __pa/__va work. On PPC32 that's not needed.


> 
>> WIth the series I send last week to add KASAN to book3e/64, we now have
>> VMALLOC above PAGE_OFFSET on all platforms so we should be able to come
>> back to the original virt_addr_valid(), based exclusively on pfn_valid()
>> for PPC64, and pfn_valid() && high_memory for PPC32 (Or maybe only for
>> PPC32 having HIGHMEM)
>>
>>
>> Christophe
>>
>>
>>>
>>> Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
>>> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>> -
>>> ---
>>>    arch/powerpc/include/asm/page.h | 10 ++++------
>>>    arch/powerpc/mm/mem.c           | 11 +++++++++++
>>>    2 files changed, 15 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
>>> index e5f75c70eda8..977835570db3 100644
>>> --- a/arch/powerpc/include/asm/page.h
>>> +++ b/arch/powerpc/include/asm/page.h
>>> @@ -131,12 +131,10 @@ static inline bool pfn_valid(unsigned long pfn)
>>>    #define virt_to_pfn(kaddr)	(__pa(kaddr) >> PAGE_SHIFT)
>>>    #define virt_to_page(kaddr)	pfn_to_page(virt_to_pfn(kaddr))
>>>    #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)
>>> -
>>> -#define virt_addr_valid(vaddr)	({					\
>>> -	unsigned long _addr = (unsigned long)vaddr;			\
>>> -	_addr >= PAGE_OFFSET && _addr < (unsigned long)high_memory &&	\
>>> -	pfn_valid(virt_to_pfn(_addr));					\
>>> -})
>>> +#ifndef __ASSEMBLY__
>>> +extern bool __virt_addr_valid(unsigned long kaddr);
>>> +#endif
>>> +#define virt_addr_valid(kaddr)	__virt_addr_valid((unsigned long) (kaddr))
>>>    
>>>    /*
>>>     * On Book-E parts we need __va to parse the device tree and we can't
>>> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
>>> index 7b0d286bf9ba..622f8bac808b 100644
>>> --- a/arch/powerpc/mm/mem.c
>>> +++ b/arch/powerpc/mm/mem.c
>>> @@ -406,3 +406,14 @@ int devmem_is_allowed(unsigned long pfn)
>>>     * the EHEA driver. Drop this when drivers/net/ethernet/ibm/ehea is removed.
>>>     */
>>>    EXPORT_SYMBOL_GPL(walk_system_ram_range);
>>> +
>>> +bool __virt_addr_valid(unsigned long kaddr)
>>> +{
>>> +	if (kaddr < PAGE_OFFSET)
>>> +		return false;
>>> +	if (is_vmalloc_addr((void *) kaddr))
>>> +		return false;
>>> +	return pfn_valid(virt_to_pfn(kaddr));
>>> +}
>>> +EXPORT_SYMBOL(__virt_addr_valid);
>>> +
>