mpk: protect memory with PROT_NONE
#7363
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This change fixes a bug with `ProtectionKey::protect`: previously it initialized each stripe with read and write permissions (i.e., `pkey_mprotect(..., PROT_READ | PROT_WRITE)` under the mistaken assumption that these permissions were MPK-specific, "what MPK permissions will we be allowed to set in the PKRU for these regions in the future?". This assumption is incorrect: the regions were immediately made accessible for reading and writing. The fix is to initially protect the regions with `PROT_NONE` and allow Wasmtime's `memory.grow` implementation to mark pages with `mprotect(..., PROT_READ | PROT_WRITE)` as usual. Whether a store can access a slice is still determined by the CPU state set in `mpk::allow`.
alexcrichton
requested review from
alexcrichton
and removed request for
pchickey
alexcrichton
approved these changes
Oct 25, 2023
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Yes, I'm working on a test to push soon. The spec tests caught this accidental read/write once I was able to actually run them. |
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This change fixes a bug with
ProtectionKey::protect: previously it initialized each stripe with read and write permissions (i.e.,pkey_mprotect(..., PROT_READ | PROT_WRITE)under the mistaken assumption that these permissions were MPK-specific, "what MPK permissions will we be allowed to set in the PKRU for these regions in the future?". This assumption is incorrect: the regions were immediately made accessible for reading and writing. The fix is to initially protect the regions withPROT_NONEand allow Wasmtime'smemory.growimplementation to mark pages withmprotect(..., PROT_READ | PROT_WRITE)as usual. Whether a store can access a slice is still determined by the CPU state set inmpk::allow.