How does stack protector work?

How does stack protector work?

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. Thus, the stack protection allows the program to abort when that happens rather than return to wherever the attacker wanted it to go.

What is stack guard?

StackGuard is a compiler extension that enhances the executable code produced by the compiler so that it detects and thwarts buffer-overflow attacks against the stack. The effect is transparent to the normal function of programs.

What is FNO stack protector?

Operation. -fno-stack-protector disables stack protection. -fstack-protector enables stack protection for vulnerable functions that contain: A character array larger than 8 bytes. A call to alloca() with either a variable size or a constant size bigger than 8 bytes.

What is GCC stack protector?

GCC and -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.

How are stack canaries vulnerable?

Stack canaries remain a widely deployed defense against memory corruption attacks. Despite their practical useful- ness, canaries are vulnerable to memory disclosure and brute-forcing attacks. We propose PCan, a new approach based on ARMv8.

What is Libssp?

libssp is one of the GNU removal show stoppers: it is used for stack. protection but it is fundamentally a compiler library. Checking r333398 and r333399 have dropped the requirement to build rtld. with an SSP-enabled libc.

What are stack cookies?

In general, a stack cookie is a randomly chosen value (4 or 8 bytes long) which is always put before the saved base pointer on the stack. Before a function returns the stack cookie will always be checked for correctness. If it is modified a program will just crash and a possible malicious code won’t be executed.

How do stack canaries work?

A stack canary is a value placed on the stack so that it will be overwritten by a stack buffer that overflows to the return address. It allows detection of overflows by verifying the integrity of the canary before function return.

What will happen once we use the option FNO stack protector in compiling ac program?

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.

Do stack canaries detect overflow?

What is a stack Canary intended to prevent?

Stack canaries, named for their analogy to a canary in a coal mine, are used to detect a stack buffer overflow before execution of malicious code can occur. This method works by placing a small integer, the value of which is randomly chosen at program start, in memory just before the stack return pointer.

What is Canary stack?

How does the stack protector feature work?

The stack protector feature itself adds a known canary to the stack during function preamble, and checks it when the function returns. If it changed, there was a stack overflow, and the program aborts. This is fine, but figuring out when to include it is the reason behind the various options.

What is the Stack Smashing Protector (SSP) compiler feature?

The Stack Smashing Protector(SSP) compiler feature helps detect stack buffer overrun by aborting if a secret value on the stack is changed. This serves a dual purpose in making the occurrence of such bugs visible and as exploit mitigation against return-oriented programming. SSP merely detects stack buffer overruns, they are not prevented.

Should I compile with -fstack-protector?

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. It will make a difference to your application.

Should stack protector be enabled by default in GCC?

In the standard/stock GCC, stack protector is off by default. However, some Linux distributions have patched GCC to turn it on by default. In my opinion, this is rather harmful, as it breaks the ability to compile anything that’s not linked against the standard userspace libraries unless the Makefile specifically disables stack protector.