Re: Fwd: New Defects reported by Coverity Scan for Das U-Boot

Abdellatif El Khlifi
2023-10-25T15:12:56Z

Hi Tom,

> > > ________________________________________________________________________________________________________
> > > *** CID 464361: Control flow issues (DEADCODE)
> > > /drivers/firmware/arm-ffa/arm-ffa-uclass.c: 148 in ffa_print_error_log()
> > > 142
> > > 143 if (ffa_id < FFA_FIRST_ID || ffa_id > FFA_LAST_ID)
> > > 144 return -EINVAL;
> > > 145
> > > 146 abi_idx = FFA_ID_TO_ERRMAP_ID(ffa_id);
> > > 147 if (abi_idx < 0 || abi_idx >= FFA_ERRMAP_COUNT)
> > > >>> CID 464361: Control flow issues (DEADCODE)
> > > >>> Execution cannot reach this statement: "return -22;".
> > > 148 return -EINVAL;
> >
> > This is a false positive.
> >
> > abi_idx value could end up matching this condition "(abi_idx < 0 || abi_idx >= FFA_ERRMAP_COUNT)".
> >
> > This happens when ffa_id value is above the allowed bounds. Example: when ffa_id is 0x50 or 0x80
> >
> > ffa_print_error_log(0x50, ...); /* exceeding lower bound */
> > ffa_print_error_log(0x80, ...); /* exceeding upper bound */
> >
> > In these cases "return -EINVAL;" is executed.
>
> So those invalid values aren't caught by the previous check that ffa_id
> falls within FFA_FIRST_ID to FFA_LAST_ID ?

I had a closer look at that and I agree that the deadcode defect is legitimate.
I already provided a fix [1].

[1]: https://lore.kernel.org/all/20231020131533.239591-1-abdellatif.elkhlifi@arm.com/

>
> > > ...
> > > ________________________________________________________________________________________________________
> > > *** CID 464360: Control flow issues (NO_EFFECT)
> > > /drivers/firmware/arm-ffa/arm-ffa-uclass.c: 207 in ffa_get_version_hdlr()
> > > 201 major = GET_FFA_MAJOR_VERSION(res.a0);
> > > 202 minor = GET_FFA_MINOR_VERSION(res.a0);
> > > 203
> > > 204 log_debug("FF-A driver %d.%d\nFF-A framework %d.%d\n",
> > > 205 FFA_MAJOR_VERSION, FFA_MINOR_VERSION, major, minor);
> > > 206
> > > >>> CID 464360: Control flow issues (NO_EFFECT)
> > > >>> This greater-than-or-equal-to-zero comparison of an unsigned value is always true. "minor >= 0".
> > > 207 if (major == FFA_MAJOR_VERSION && minor >= FFA_MINOR_VERSION) {
> >
> > Providing the facts that:
> >
> > #define FFA_MINOR_VERSION (0)
> > u16 minor;
> >
> > Yes, currently this condition is always true: minor >= FFA_MINOR_VERSION
> >
> > However, we might upgrade FFA_MINOR_VERSION in the future. If we remove the "minor >= FFA_MINOR_VERSION" ,
> > non compatible versions could pass which we don't want.
> >
> > To keep this code scalable, I think it's better to keep this condition.
>
> OK, thanks this makes sense as an intentional change for future sanity
> checking.
>
> > > ________________________________________________________________________________________________________
> > > *** CID 464359: (PASS_BY_VALUE)
> > > /drivers/firmware/arm-ffa/arm-ffa-uclass.c: 168 in invoke_ffa_fn()
> > > 162 * @args: FF-A ABI arguments to be copied to Xn registers
> > > 163 * @res: FF-A ABI return data to be copied from Xn registers
> > > 164 *
> > > 165 * Calls low level SMC implementation.
> > > 166 * This function should be implemented by the user driver.
> > > 167 */
> > > >>> CID 464359: (PASS_BY_VALUE)
> > > >>> Passing parameter args of type "ffa_value_t" (size 144 bytes) by value, which exceeds the low threshold of 128 bytes.
> > > 168 void __weak invoke_ffa_fn(ffa_value_t args, ffa_value_t *res)
> >
> > We are using invoke_ffa_fn with the same arguments as in linux. The aim is to use the same interfaces as in the Linux FF-A
> > driver to make porting code easier.
> >
> > In Linux, args is passed by value [1].
> > ffa_value_t is a structure with 18 "unsigned long" fields. So, the size is fixed.
> >
> > [1]: invoke_ffa_fn arguments in the Linux FF-A driver
> >
> > https://elixir.bootlin.com/linux/v6.6-rc6/source/drivers/firmware/arm_ffa/driver.c#L115
> > https://elixir.bootlin.com/linux/v6.6-rc6/source/drivers/firmware/arm_ffa/driver.c#L54
> > https://elixir.bootlin.com/linux/v6.6-rc6/source/drivers/firmware/arm_ffa/common.h#L15
> >
> > [2]: include/linux/arm-smccc.h
>
> So this is intentional, OK.
>
> >
> > > 169 {
> > > 170 }
> > > 171
> > > 172 /**
> > > 173 * ffa_get_version_hdlr() - FFA_VERSION handler function
> > > /drivers/firmware/arm-ffa/ffa-emul-uclass.c: 673 in invoke_ffa_fn()
> > > 667 * invoke_ffa_fn() - SMC wrapper
> > > 668 * @args: FF-A ABI arguments to be copied to Xn registers
> > > 669 * @res: FF-A ABI return data to be copied from Xn registers
> > > 670 *
> > > 671 * Calls the emulated SMC call.
> > > 672 */
> > > >>> CID 464359: (PASS_BY_VALUE)
> > > >>> Passing parameter args of type "ffa_value_t" (size 144 bytes) by value, which exceeds the low threshold of 128 bytes.
> > > 673 void invoke_ffa_fn(ffa_value_t args, ffa_value_t *res)
> >
> > Same feedback as above.
>
> Thanks. I'll update the last 3 CIDs shortly.

Thanks Tom :)

Cheers,
Abdellatif