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    SubjectRe: [PATCH RFC v2 5/6] staging: r8188eu: add error handling of rtw_read32
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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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