Messages in this thread | | | Subject | Re: [PATCH RFC v2 5/6] staging: r8188eu: add error handling of rtw_read32 | From | Pavel Skripkin <> | Date | Tue, 24 Aug 2021 11:47:12 +0300 |
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On 8/24/21 11:38 AM, Fabio M. De Francesco wrote: > On Tuesday, August 24, 2021 8:40:18 AM CEST Pavel Skripkin wrote: >> On 8/24/21 3:10 AM, Fabio M. De Francesco wrote: >> > On Tuesday, August 24, 2021 1:33:46 AM CEST Phillip Potter wrote: >> >> On Sun, 22 Aug 2021 at 15:36, Pavel Skripkin <paskripkin@gmail.com> wrote: >> >> > -static u32 usb_read32(struct intf_hdl *pintfhdl, u32 addr) >> >> > +static int usb_read32(struct intf_hdl *pintfhdl, u32 addr, u32 *data) >> >> > { >> >> > u8 requesttype; >> >> > u16 wvalue; >> >> > u16 len; >> >> > - __le32 data; >> >> > + int res; >> >> > + __le32 tmp; >> >> > + >> >> > + if (WARN_ON(unlikely(!data))) >> >> > + return -EINVAL; >> >> > >> >> > requesttype = 0x01;/* read_in */ >> >> > >> >> > wvalue = (u16)(addr & 0x0000ffff); >> >> > len = 4; >> >> > >> >> > - usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype); >> >> > + res = usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype); >> >> > + if (res < 0) { >> >> > + dev_err(dvobj_to_dev(pintfhdl->pintf_dev), "Failed to read 32 bytes: %d\n", res); >> >> > + } else { >> >> > + /* Noone cares about positive return value */ >> >> > + *data = le32_to_cpu(tmp); >> >> > + res = 0; >> >> > + } >> >> > >> >> > - return le32_to_cpu(data); >> >> > + return res; >> >> > } >> >> >> >> Dear Pavel, >> >> >> >> OK, found the issue with decoded stack trace after reviewing this >> >> usb_read32 function. Your line: >> >> res = usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype); >> >> >> >> should read: >> >> res = usbctrl_vendorreq(pintfhdl, wvalue, &tmp, len, requesttype); >> > >> > Dear Philip, >> > >> > No, it should read: >> > >> > res = usbctrl_vendorreq(pintfhdl, wvalue, data, len, requesttype); >> > >> > I suspect that Pavel didn't notice he was reusing a line of the old code >> > wth no due changes. >> > >> >> With this change, the driver runs fine with no crashes/oopses. I will >> >> explain the issue but you can probably see already, so I hope I'm not >> >> coming across as patronising, just trying to be helpful :-) >> >> >> >> Essentially, you are taking the address of the data function parameter >> >> on this line with &data, a pointer to u32, which is giving you a >> >> pointer to a pointer to u32 (u32 **) for this function parameter >> >> variable. When passed to usbctrl_vendorreq, it is being passed to >> >> memcpy inside this function as a void *, meaning that memcpy >> >> subsequently overwrites the value of the memory address inside data to >> >> point to a different location, which is problem when it is later >> >> deferenced at: >> >> *data = le32_to_cpu(tmp); >> >> causing the OOPS >> >> >> >> Also, as written, you can probably see that tmp is uninitialised. This >> >> looks like a typo, so guessing this wasn't your intention. Anyhow, >> >> with that small change, usbctrl_vendorreq reads into tmp, which is >> >> then passed to le32_to_cpu whose return value is stored via the >> >> deferenced data ptr (which now has its original address within and not >> >> inadvertently modified). Hope this helps, and I'd be happy to Ack the >> >> series if you want to resend this patch. Many thanks. >> > >> > I think that another typo is having 'tmp', because that variable is unnecessary >> > and "*data = le32_to_cpu(tmp);" is wrong too. >> > >> > Now I also see that also usb_read16() is wrong, while usb_read8() (the one that >> > I had read yesterday) is the only correct function of the three usb_read*(). >> > >> >> Hi, guys! >> >> >> Sorry for breaking your system, Phillip. This code was part of "last >> minute" changes and yes, it's broken :) >> >> I get what Phillip said, because I _should_ read into tmp variable >> instead of directly to data, but I don't get Fabio's idea, sorry. > > Hi Pavel, > > I (wrongly?) assumed from the prototype of usb_read32() that u32 *data is in native > endianness. So, I didn't see the necessity of using _le32 tmp and then convert that tmp > with le32_to_cpu(). > > I simply thought that data could be passed to usbctrl_vendorreq as it-is. > >> Data from chip comes in little-endian, so we _should_ convert it to >> cpu's endian. Temp variable is needed to make smatch and all other >> static anylis tools happy about this code. > > Now that you explained that "Data from chip comes in little-endian", obviously > I must agree with you that the code needs tmp and that tmp must be > swapped by le32_to_cpu(), ahead of assigning it to *data. > > Just a curiosity... Since I was not able to see that *data is returned in little endian, > can you please point me where in the code you found out that it is? There must > be some place in the code that I'm unable to find and see that *data is LE. > > Thanks in advance, > > Fabio
Hi, Fabio!
previous usb_read16() realization, which is 100% right:
static u16 usb_read16(struct intf_hdl *pintfhdl, u32 addr) { u8 requesttype; u16 wvalue; u16 len; __le32 data;
requesttype = 0x01;/* read_in */ wvalue = (u16)(addr & 0x0000ffff); len = 2; usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype);
return (u16)(le32_to_cpu(data) & 0xffff); }
Bases on this code, I think, it's oblivious, that data comes in little-endian. That's why I leaved temp variable for casting le32 to cpu's endianess.
I could just read into u{16,32} * and then make smth like
*data = le32_to_cpu(*data)
but static analysis tools will complain about wrong data type passed to le32_to_cpu()
+ Phillip tested fixed v2 version and it worked well for him. I guess, Phillip was able to spot weird driver behavior, if this cast is wrong.
With regards, Pavel Skripkin
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