From: Saurabh Singh Sengar <ssengar@xxxxxxxxxxxxx> Sent: Tuesday, August 15, 2023 7:59 AM > > > -----Original Message----- > > From: Michael Kelley (LINUX) <mikelley@xxxxxxxxxxxxx> > > Sent: Tuesday, August 15, 2023 1:46 AM > > To: Michael Kelley (LINUX) <mikelley@xxxxxxxxxxxxx>; Saurabh Singh Sengar > > <ssengar@xxxxxxxxxxxxx>; Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>; > > KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang > > <haiyangz@xxxxxxxxxxxxx>; wei.liu@xxxxxxxxxx; Dexuan Cui > > <decui@xxxxxxxxxxxxx> > > Cc: linux-hyperv@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > > Subject: RE: [PATCH] hv: hyperv.h: Replace one-element array with flexible- > > array member > > > > From: Michael Kelley (LINUX) <mikelley@xxxxxxxxxxxxx> Sent: Monday, > > August 14, 2023 1:10 PM > > > From: Saurabh Singh Sengar <ssengar@xxxxxxxxxxxxx> Sent: Tuesday, > > > August 8, 2023 2:49 AM > > > > > > > > [snip] > > > > > > > > > > Thanks for your comment, I wanted to have this discussion. > > > > > > > > Before sending this patch, I was contemplating whether or not to make this change. > > > > Through my analysis, I arrived at the conclusion that the initial > > > > validation code wasn't entirely accurate. And with the proposed changes it gets more accurate. > > > > IMHO it is more accurate to exclude the size of 'ranges' in the header. > > > > > > > > With my limited understanding of this driver, the current "header size validation" > > > > is only to make sure that header is correct. So, that we fetch the > > > > range_cnt and xfer_pageset_id correctly from it. For this to be done > > > > I don't find any reason to include the size of ranges in this check. > > > > With inclusion of ranges we are checking the first 'struct > > > > vmtransfer_page_range' size as well which is not required for fetching above two values. > > > > > > > > Once we have the count of ranges we will anyway check the sanity of > > > > ranges with NETVSC_XFER_HEADER_SIZE. This will check "count * (struct vmtransfer_page_range)" > > > > Which is present few lines after. > > > > > > > > For a ranges count = 1, I don't see there is any difference between > > > > both the checks as of today. > > > > > > > > Please let me know you opinion if you don't find my explanation reasonable. > > > > > > > > I don't see any other place this structure's size change will affect. > > > > > > > > > > Got it. I have now carefully looked at the netvsc_receive() code > > > myself, and I agree with you. With the 1 element array, the validation in > > > netvsc_receive() could have generated a false positive if the > > > range_cnt is zero. But I don't think a zero range_cnt ever happens, > > > so the false positive never happens. With the change to use a > > > flexible array, the validation is now correct even with a range_cnt of zero. > > > > > > Please add a note to the commit message for this patch: The > > > validation code in the netvsc driver is affected by changing the > > > struct size, but the effects have been examined and have been determined > > to be appropriate. > > > > > > > One other thought: Could this change affect user space DPDK code that is > > processing netvsc packets? > > + Long Li > > I am aware that DPDK code uses uio_hv_generic driver to have its own > implementation of userspace netvsc and the changes here are only confined > to kernel's netvsc driver. Thus, I believe this code shouldn't affect anything > in userspace netvsc implementation. > > I also browsed the DPDK code and found that DPDK has this struct implemented as > struct vmbus_chanpkt_rxbuf and that already has flexible array member. > > https://github.com/DPDK/dpdk/blob/v23.07/drivers/bus/vmbus/rte_vmbus_reg.h#L182 > Sounds good to me. Thanks for checking. Michael
