Table of Contents
What does Fstack protector do?
-fstack-protector enables stack protection for vulnerable functions that contain: A character array larger than 8 bytes. An 8-bit integer array larger than 8 bytes. A call to alloca() with either a variable size or a constant size bigger than 8 bytes.
What is __ Stack_chk_guard?
The checking code of the stack protection mechanism stores a copy of __stack_chk_guard in a register or on the stack. This copy is used to check the value of the guard variable. Therefore, the value of __stack_chk_guard can be changed during the life of the program.
How do stack canaries work?
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 __ 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.
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.
What is stack canary & Why do we use it?
Stack canaries or security cookies are tell-tale values added to binaries during compilation to protect critical stack values like the Return Pointer against buffer overflow attacks.
How canary prevent buffer overflow?
Typically, buffer overflow protection modifies the organization of data in the stack frame of a function call to include a “canary” value that, when destroyed, shows that a buffer preceding it in memory has been overflowed. This provides the benefit of preventing an entire class of attacks.
How do I overcome stack overflow?
One method to prevent stack overflow is to track the stack pointer with test and measurement methods. Use timer interrupts that periodically check the location of the stack pointer, record the largest value, and watch that it does not grow beyond that value.
What is stack smashing in Linux?
Stack smashing is a form of vulnerability where the stack of a computer application or OS is forced to overflow. This may lead to subverting the program/system and crashing it. A stack, a first-in last-out circuit, is a form of buffer holding intermediate results of operations within it.
Why is stack non-executable?
Non-executable stack (NX) is a virtual memory protection mechanism to block shell code injection from executing on the stack by restricting a particular memory and implementing the NX bit. But this technique is not really worthy against return to lib attacks, although they do not need executable stacks.
What is an executable stack?
Executable stack is necessary in some cases such as GCC trampoline for nested functions. A trampoline is a small piece of code that is created at run time when the address of a nested function is taken. It normally resides on the stack, in the stack frame of the containing function.
Do stack canaries prevent overflow?
Where is stack canary placed?
Stack Canaries are a secret value placed on the stack which changes every time the program is started. Prior to a function return, the stack canary is checked and if it appears to be modified, the program exits immeadiately.
What is a canary buffer overflow?
What happens when stack is full?
If the stack is full, then it is said to be an Overflow condition. Pop: Removes an item from the stack. The items are popped in the reversed order in which they are pushed. If the stack is empty, then it is said to be an Underflow condition.
How to disable -fstack-protection in kernel?
While configuring the kernel., Under Kernel Feature —> Disabling “Enable -fstack-protector buffer overflow detection” fixed this problem. It was because my toolchain gcc 4.0.1 did not have -fstack-protection feature.
What is “-fstack-protector-strong”?
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.
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 default-fstack-protector?
Since traditionally stack overflows happen with string-based manipulations, the default ( -fstack-protector ), only includes the canary code when a function defines an 8 ( –param=ssp-buffer-size=N, N=8 by default) or more byte local character array.