So, it's okay to trap when indexing from one object to another and then dereferencing, or when constructing a non-derived pointer to an object in any other way and dereferencing it? That's what memory tagging will cause, since it aims to have the tags not match in those cases.
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No. Language says that there is no such thing as an object - it's all integer-addressed bytes. Language further acknowledges that virtual memory and trap-on-access exists. It's simple: you just write a spec of reality instead of playing silly games.
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Okay, so you don't want SPARC ADI and ARM MTE to be used as designed in a standards compliant C implementation which the current C standard permits. It's not playing games. Having at least a weak approximation of memory safety like tagging and various other features is important.
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I just made the opposite point: that MTE works fine if the language is spec'd the way I'm proposing. It allows them to be used as designed by removing the notion of malloc from the language.
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It doesn't only impact malloc. It's designed to be usable for stack frames instead of stack canaries too. It also impacts usage of the pointers derived from what gets returned by malloc even in an implementation only using it for malloc. It doesn't only impact the malloc memory.
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None of what I said relies on this being restricted to impacting malloc. You don't need UB in the language to say that stack canaries are a thing.
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I'm talking about memory tagging as a replacement for stack canaries, not stack canaries. I'm not sure why you're responding about stack canaries. Memory tagging the stack frame makes it so that trying to use pointers to the stack frame to access memory outside it will trap.
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Memory tagging works fine with the spec I'm proposing. So do stack canaries. I'm making the point that the security technologies that you are interested in (and that I'm also interested in) work fine if the language is more strongly specified.
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Sure, and as I've stated many times in this conversation, I would like for C to be more strongly specified. However, defining something like signed integer overflow as guaranteed to wrap would be a step backwards for implementations that want to make it safer such as trapping.
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But making it traps breaks real C code, so it can't be what the spec says.
Good specs respect their existing clients!
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Forbidding trapping also breaks widely deployed existing implementations, so you can't do that either per your own rules, sorry.
We have a case of clients disagreeing. I would put it to a vote. My clients will win it no problem.
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Oh, right, so you weren't actually being truthful about respecting existing implementations and deployments of the standard. It fits with how you've been arguing the entire time. You are being incredibly dishonest and manipulative along with misrepresenting what I've been saying.
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It's always implemented in software via hardware features. The features vary in performance. Jump-on-overflow is a lot worse than architectures with support for enabling a trapping mode, whether it's strict or propagates a poison value that can never be accessed (since it traps).
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