Re: [PATCH kernel] KVM: PPC: Book3S: Suppress warnings when allocating too big memory slots

On 02/09/2021 00:59, Fabiano Rosas wrote:
> Alexey Kardashevskiy <[email protected]> writes:
> 
>> The userspace can trigger "vmalloc size %lu allocation failure: exceeds
>> total pages" via the KVM_SET_USER_MEMORY_REGION ioctl.
>>
>> This silences the warning by checking the limit before calling vzalloc()
>> and returns ENOMEM if failed.
>>
>> This does not call underlying valloc helpers as __vmalloc_node() is only
>> exported when CONFIG_TEST_VMALLOC_MODULE and __vmalloc_node_range() is not
>> exported at all.
>>
>> Spotted by syzkaller.
>>
>> Signed-off-by: Alexey Kardashevskiy <[email protected]>
>> ---
>>   arch/powerpc/kvm/book3s_hv.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index 474c0cfde384..a59f1cccbcf9 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -4830,8 +4830,12 @@ static int kvmppc_core_prepare_memory_region_hv(struct kvm *kvm,
>>   	unsigned long npages = mem->memory_size >> PAGE_SHIFT;
>>
>>   	if (change = KVM_MR_CREATE) {
>> -		slot->arch.rmap = vzalloc(array_size(npages,
>> -					  sizeof(*slot->arch.rmap)));
>> +		unsigned long cb = array_size(npages, sizeof(*slot->arch.rmap));
> 
> What does cb mean?

"count of bytes"

This is from my deep Windows past :)

https://docs.microsoft.com/en-us/windows/win32/stg/coding-style-conventions


> 
>> +
>> +		if ((cb >> PAGE_SHIFT) > totalram_pages())
>> +			return -ENOMEM;
>> +
>> +		slot->arch.rmap = vzalloc(cb);
>>   		if (!slot->arch.rmap)
>>   			return -ENOMEM;
>>   	}

-- 
Alexey