Batched user access support
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Cover letter [PATCH 0/3] Batched user access support
Quoted 8 lines · Will Deacon
From an implementation and performance point of view, this can certainly be used by arm64. My only concern is that we increase the region where PAN is disabled (that is, user accesses are permitted). Currently, that's carefully restricted to the single userspace access, but now it could easily include accesses to the kernel stack, perhaps even generated as a result of compiler spills.
Quoted 4 lines
I'm pretty unimaginative when it comes to security exploits, but that does sound worse than the current implementation from a security perspective.
It is, but it is a tradeoff. It is way better than opening it up for the entire kernel. In the end the only real way to avoid this is compiler support, which I *have* discussed for x86 with the gcc people.
gcc could avoid the back-to-back on and off and even batch accesses by
moving them into registers.
-hpa