CWE-480: Use of Incorrect Operator

Intro: The following C/C++ and C# examples attempt to validate an int input parameter against the integer value 100.

Body: However, the expression to be evaluated in the if statement uses the assignment operator "=" rather than the comparison operator "==". The result of using the assignment operator instead of the comparison operator causes the int variable to be reassigned locally and the expression in the if statement will always evaluate to the value on the right hand side of the expression. This will result in the input value not being properly validated, which can cause unexpected results.

int isValid(int value) { if (value=100) { printf("Value is valid\n"); return(1); } printf("Value is not valid\n"); return(0); }

Intro: The following C/C++ example shows a simple implementation of a stack that includes methods for adding and removing integer values from the stack. The example uses pointers to add and remove integer values to the stack array variable.

Body: The push method includes an expression to assign the integer value to the location in the stack pointed to by the pointer variable.

#define SIZE 50 int *tos, *p1, stack[SIZE]; void push(int i) { p1++; if(p1==(tos+SIZE)) { // Print stack overflow error message and exit } *p1 == i; } int pop(void) { if(p1==tos) { // Print stack underflow error message and exit } p1--; return *(p1+1); } int main(int argc, char *argv[]) { // initialize tos and p1 to point to the top of stack tos = stack; p1 = stack; // code to add and remove items from stack ... return 0; }

Intro: The example code below is taken from the CVA6 processor core of the HACK@DAC'21 buggy OpenPiton SoC. Debug access allows users to access internal hardware registers that are otherwise not exposed for user access or restricted access through access control protocols. Hence, requests to enter debug mode are checked and authorized only if the processor has sufficient privileges. In addition, debug accesses are also locked behind password checkers. Thus, the processor enters debug mode only when the privilege level requirement is met, and the correct debug password is provided.

Body: The following code [REF-1377] illustrates an instance of a vulnerable implementation of debug mode. The core correctly checks if the debug requests have sufficient privileges and enables the debug_mode_d and debug_mode_q signals. It also correctly checks for debug password and enables umode_i signal.

module csr_regfile #( ... // check that we actually want to enter debug depending on the privilege level we are currently in unique case (priv_lvl_o) riscv::PRIV_LVL_M: begin debug_mode_d = dcsr_q.ebreakm; ... riscv::PRIV_LVL_U: begin debug_mode_d = dcsr_q.ebreaku; ... assign priv_lvl_o = (debug_mode_q || umode_i) ?  riscv::PRIV_LVL_M : priv_lvl_q; ... debug_mode_q  <= debug_mode_d; ...