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

[Tom Rini <trini@konsulko.com>]

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On Fri, Oct 20, 2023 at 12:57:47PM +0100, Abdellatif El Khlifi wrote:
> 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 ?

> > ... 
> > ________________________________________________________________________________________________________
> > *** 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.

-- 
Tom

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