memory tagging should be a game changer for C and C++; get with the program, @intel and @apple!!pic.twitter.com/z2vXAtTb7z
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memory tagging should be a game changer for C and C++; get with the program, @intel and @apple!!pic.twitter.com/z2vXAtTb7z
I'm going to be that jerkface and predict that MTE won't do all that much. It's a pretty weak mitigation that requires a lot of work to adopt.
MTE requires relatively little work to adopt (I say this as someone who's adamant about not adopting invasive "hardening" snakeoil like CET) and completely closes off huge classes of vulns.
Sequential buffer overflows (out of object) are completely impossible. Attack of heap metadata is impossible without ability to craft upper ptr bits. Clobbering new object via UAF is impossible to prevent 100% but statistically very likely to trap.
…unless the attacker can get the tag of the freed area somehow, which is one instruction away. That’s the scary part.
If they have code execution already, you're outside the scope of what MTE is protecting against. That's the scope of anti-ROP snakeoil like CET. The point of MTE is to prevent getting there in the first place.
Scenario: Attacker has a UAF vuln and some ability to read the address of newly allocated pointers via a leak. Attacker causes object to be freed with a dangling pointer. Attacker repeatedly reallocates and frees objects in that area, checking pointers, until tag matches.
Then UAF becomes exploitable again. This shows the weakness of 4-bit tag: doesn’t take many allocations to get a collision.
Or just get lucky. A drive-by exploit that "only" takes over 1 in 16 devices is pretty bad.
Well, presumably the allocator makes sure that new allocations don’t have the same tag as the old one, so you’d need at least two free->realloc->realloc cycles, but yeah.
Exactly. Likely you increment it mod 14 or 15 each time around (reserving 1-2 tags for special uses), to maximize number of generations needed for a collision.
If your allocator also always serves up LRU free chunk, you can make the period for reuse of the same pointer+tag considerably larger.
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