What is Fstack protector strong?

What is Fstack protector strong?

-fstack-protector-strong enables stack protection for vulnerable functions that contain: An array of any size and type. A call to alloca() . A local variable that has its address taken.

What is GCC stack protector?

GCC and -fstack-protector This includes functions that call alloca, and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits. If a guard check fails, an error message is printed and the program exits.

How does GCC stack protector work?

GCC has supported stack protection for some time. The basic idea behind stack protection is to push a “canary” (a randomly chosen integer) on the stack just after the function return pointer has been pushed. The canary value is then checked before the function returns; if it has changed, the program will abort.

Why do we need to include the command FNO stack protector while compiling?

If you compile with -fstack-protector , then there will be a little more space allocated on the stack and a little more overhead on entry to and return from a function while the code sets up the checks and then actually checks whether you’ve overwritten the stack while in the function.

What is __ Stack_chk_guard?

__stack_chk_guard which contains the initial value of the stack protector, and, __stack_chk_fail which is called when a stack smashing is detected. This function should never return.

What does Fstack protector all do?

-fstack-protector-all adds stack protection to all functions regardless of their vulnerability. -fstack-protector-strong enables stack protection for vulnerable functions that contain: An array of any size and type. A call to alloca() .

What is stack smashing in C?

Stack smashing occurs when a buffer overflow overwrites data in the memory allocated to the execution stack. More often, a buffer overflow in the stack segment can lead to an attacker executing arbitrary code by overwriting a pointer address to which control is (eventually) transferred.

Can StackGuard prevent stack smashing?

The StackGuard compiler provides robust automatic protection against the all-too-com- mon problem of stack smashing vulnerabili- ties.

What does stack protector do?

Here’s how it plays out: If you have a bug and make a buffer change based on something an attacker can control, that attacker can overwrite the return address or similar portions of the stack to cause it to execute their code instead of your code. Stack protection will abort your program if it detects this happening.

What is __ Stack_chk_fail?

__stack_chk_fail , a callback function that is invoked when a stack buffer overflow is detected. This function shall abort the function that called it with a message that a stack buffer overflow has been detected, and then halt the program via exit , abort , or a custom panic handler. This function must not return!

How do I use Fstack protector?

-fstack-protector This is done by adding a guard variable to functions with vulnerable objects. This includes functions that call alloca, and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits.

Is there a stack protector in GCC 4.9?

There will be a new option in gcc 4.9 named “ -fstack-protector-strong “, which offers an improved version of “ -fstack-protector ” without going all the way to “ -fstack-protector-all “. The stack protector feature itself adds a known canary to the stack during function preamble, and checks it when the function returns.

Which is the stack protection for fstack function?

-fstack-protector-all adds stack protection to all functions regardless of their vulnerability. -fstack-protector-strong enables stack protection for vulnerable functions that contain:

How big is the kernel with fstack protector turned on?

The kernel with -fstack-protector turned on is 0.33% larger and covers 2.81% of the functions in the kernel. For -fstack-protector-strong, those numbers are an increase of 2.4% in code size over an unprotected kernel, but 20.5% of the functions are covered.

How to avoid stack smashing attacks with GCC?

Emit extra code to check for buffer overflows, such as stack smashing attacks. This is done by adding a guard variable to functions with vulnerable objects. This includes functions that call alloca, and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits.