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mpk: reenable MPK support with vendor string check #7513

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merged 2 commits into from
Nov 9, 2023
Merged

mpk: reenable MPK support with vendor string check #7513

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998c766
mpk: reenable MPK support with vendor string check
abrown Nov 9, 2023
ae96efc
review: use `u32::from_le_bytes` to self-document the string check
abrown Nov 9, 2023
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24 changes: 16 additions & 8 deletions crates/runtime/src/mpk/pkru.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,16 +53,24 @@ pub fn write(pkru: u32) {
}
}

/// Check the `ECX.PKU` flag (bit 3) of the `07h` `CPUID` leaf; see the
/// Intel Software Development Manual, vol 3a, section 2.7.
/// Check the `ECX.PKU` flag (bit 3) of the `07h` `CPUID` leaf; see the Intel
/// Software Development Manual, vol 3a, section 2.7. This flag is only set on
/// Intel CPUs, so this function also checks the `CPUID` vendor string.
pub fn has_cpuid_bit_set() -> bool {
// TODO: disable MPK support until the following issue is resolved:
// https://github.com/bytecodealliance/wasmtime/issues/7445
if true {
return false;
}
let result = unsafe { std::arch::x86_64::__cpuid(0x07) };
(result.ecx & 0b100) != 0
is_intel_cpu() && (result.ecx & 0b100) != 0
}

/// Check the `CPUID` vendor string for `GenuineIntel`; see the Intel Software
/// Development Manual, vol 2a, `CPUID` description.
pub fn is_intel_cpu() -> bool {
// To read the CPU vendor string, we pass 0 in EAX and read 12 ASCII bytes
// from EBX, EDX, and ECX (in that order).
let result = unsafe { std::arch::x86_64::__cpuid(0) };
// Then we check if the vendor string matches "GenuineIntel".
result.ebx == u32::from_le_bytes(*b"Genu")
&& result.edx == u32::from_le_bytes(*b"ineI")
&& result.ecx == u32::from_le_bytes(*b"ntel")
}

#[cfg(test)]
Expand Down