Messages in this thread | | | Subject | Re: [PATCH v4 06/21] hwmon: (mr75203) fix multi-channel voltage reading | Date | Wed, 7 Sep 2022 08:15:36 +0300 | From | "Farber, Eliav" <> |
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On 9/6/2022 5:10 PM, Andy Shevchenko wrote: > On Tue, Sep 06, 2022 at 08:33:41AM +0000, Eliav Farber wrote: >> Fix voltage allocation and reading to support all channels in all VMs. >> Prior to this change allocation and reading were done only for the first >> channel in each VM. >> This change counts the total number of channels for allocation, and >> takes >> into account the channel offset when reading the sample data register. > > ... > >> + total_ch = ch_num * vm_num; >> + in_config = devm_kcalloc(dev, total_ch + 1, >> sizeof(*in_config), GFP_KERNEL); > > Strictly speaking this should be `size_add(size_mul(...) ...)` > construction > from overflow.h. > > total_ch = size_mul(ch_num, vm_num); > in_config = devm_kcalloc(dev, size_add(total_ch, 1), > sizeof(*in_config), GFP_KERNEL); > > Alternatively before doing all these, add a check > > if (array3_size(ch_num, vm_num, sizeof(*in_config)) < > SIZE_MAX - sizeof(*in_config)) > return -EOVERFLOW; > > But this is a bit monstrous. Seems like the above looks and feels better. > > Also for backporting purposes perhaps it's fine to do without using > those macro > helpers. According to the driver code total_ch is a u32 variable while vm_num and ch_num are both limited to a value of 31:
#define VM_NUM_MSK GENMASK(20, 16) #define VM_NUM_SFT 16 #define CH_NUM_MSK GENMASK(31, 24) #define CH_NUM_SFT 24
In addition the PVT Controller Series 3+ Specification mentions that the actual maximum values are even smaller – 8 for vm_num and 16 for ch_num. Therefore we are very far from a scenario of an overflow. Do you still think overflow protection in necessary?
-- Thanks, Eliav
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