Sure, and most C code is full of memory corruption bugs even including lots of latent memory corruption that occurs in regular usage rather than just edge cases (like an exploit). I'm well aware that real world C code is filled with lots of undefined behavior. It hinders my work.
Conversation
That's not how undefined behavior is defined. That's your own definition, and it's not clear to me how your definition is meant to work. For example, you seem okay with uninitialized memory from malloc changing value, but yet not local variables, which is very arbitrary.
1
Since you want to permit out-of-bounds accesses, you want to forbid real world partial / full memory safety implementations that are being deployed. You would even forbid _FORTIFY_SOURCE, not just -fsanitize=object-size. Another good example would be function pointer typing.
1
The C standard forbids calling a function pointer that has a mismatched type with the function. So for example, calling a function `void foo(char *)` via `void (*foo)(void *)` is undefined. This is what type-based Control Flow Integrity (CFI) enforces to mitigate exploitation.
1
That's the reality of C. People use implementations including runtime optimizations like MADV_FREE and assorted mitigations that enforce subsets of type and memory safety. There are also implementations without a fixed stack, with garbage collection, etc. It permits all this.
1
It's a large part of why people use C in the first place. It's extremely portable and permits all kinds of different implementations. It can be compiled to the JVM with GC or WebAssembly. It supports architectures with different kinds of stacks or without traditional stacks, etc.
1
When an architecture / platform introduces a change like using shadow stacks (Intel CET, LLVM ShadowCallStack) to protect control flow, it's broadly compatible, because C doesn't permit programs to make all kinds of assumptions about how the stack and function calls work.
2
And by the way, I think the vast majority of C applications / libraries compiled for Linux have _FORTIFY_SOURCE enabled. If you define indexing from one object to another and dereferencing the pointer, you're declaring that to be broken, along with tooling like ASan, etc.
1
So you can define that to be broken if you like. That doesn't mean that the spec has to be maximally permissive. It's OK to say that more secure variants of C deviate from whatever the spec says. A well-defined spec would make it easier to talk about how tools change behavior.
1
They don't deviate from the specification though. They're standard and code is required to work with them. You want to make it more difficult to make secure implementations of C, and to permit code not to be portable to them, which is a major step backwards for security.
Architectures are providing more of these things in hardware, like shadow stacks, memory tagging and hardware-based call frames. It's reducing portability of the language to both existing and future implementations too. One of the main strengths of C is that kind of portability.
1
Show replies
No, I want a -fno-bullshit flag so that you can write the systems code that underpins all the other stuff. Defining behavior precisely doesn’t mean others can’t define it differently.
1
No, you definitely want a lot more of that, and you've got your own very arbitrary and subjective rules for what should be allowed. You want to disallow many safety / security features that are broadly used in production today. You want to disallow many optimizations. And more.
1
Show replies