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

Abdellatif El Khlifi
2023-10-20T11:58:04Z

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.

> ...
> ________________________________________________________________________________________________________
> *** 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.

> ...
> ________________________________________________________________________________________________________
> *** 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

> 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.

Cheers,
Abdellatif