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mpk: maintain mapping of pkey ID to stripe ID #7353

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merged 1 commit into from
Oct 24, 2023
Merged

mpk: maintain mapping of pkey ID to stripe ID #7353

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27 changes: 15 additions & 12 deletions crates/runtime/src/mpk/enabled.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,11 +26,12 @@ pub fn keys() -> &'static [ProtectionKey] {
if is_supported() {
while let Ok(key_id) = sys::pkey_alloc(0, 0) {
debug_assert!(key_id < 16);
// UNSAFETY: here we unsafely assume that the system-allocated pkey
// will exist forever.
let pkey = ProtectionKey(key_id);
debug_assert_eq!(pkey.as_stripe(), allocated.len());
allocated.push(pkey);
// UNSAFETY: here we unsafely assume that the system-allocated
// pkey will exist forever.
allocated.push(ProtectionKey {
id: key_id,
stripe: allocated.len().try_into().unwrap(),
});
}
}
allocated
Expand Down Expand Up @@ -58,7 +59,10 @@ pub fn allow(mask: ProtectionMask) {
/// [`ProtectionMask`]; any accesses to unmarked pages result in a fault
/// - drop the key
#[derive(Clone, Copy, Debug)]
pub struct ProtectionKey(u32);
pub struct ProtectionKey {
id: u32,
stripe: u32,
}

impl ProtectionKey {
/// Mark a page as protected by this [`ProtectionKey`].
Expand All @@ -75,7 +79,7 @@ impl ProtectionKey {
let addr = region.as_mut_ptr() as usize;
let len = region.len();
let prot = sys::PROT_READ | sys::PROT_WRITE;
sys::pkey_mprotect(addr, len, prot, self.0).with_context(|| {
sys::pkey_mprotect(addr, len, prot, self.id).with_context(|| {
format!(
"failed to mark region with pkey (addr = {addr:#x}, len = {len}, prot = {prot:#b})"
)
Expand All @@ -87,8 +91,7 @@ impl ProtectionKey {
///
/// This function assumes that the kernel has allocated key 0 for itself.
pub fn as_stripe(&self) -> usize {
debug_assert!(self.0 != 0);
self.0 as usize - 1
self.stripe as usize
}
}

Expand Down Expand Up @@ -117,7 +120,7 @@ impl ProtectionMask {
/// Include `pkey` as another allowed protection key in the mask.
#[inline]
pub fn or(self, pkey: ProtectionKey) -> Self {
let mask = pkru::DISABLE_ACCESS ^ 0b11 << (pkey.0 * 2);
let mask = pkru::DISABLE_ACCESS ^ 0b11 << (pkey.id * 2);
Self(self.0 & mask)
}
}
Expand Down Expand Up @@ -178,13 +181,13 @@ mod tests {
allow(ProtectionMask::all());
assert_eq!(0, pkru::read());

allow(ProtectionMask::all().or(ProtectionKey(5)));
allow(ProtectionMask::all().or(ProtectionKey { id: 5, stripe: 0 }));
assert_eq!(0, pkru::read());

allow(ProtectionMask::zero());
assert_eq!(0b11111111_11111111_11111111_11111100, pkru::read());

allow(ProtectionMask::zero().or(ProtectionKey(5)));
allow(ProtectionMask::zero().or(ProtectionKey { id: 5, stripe: 0 }));
assert_eq!(0b11111111_11111111_11110011_11111100, pkru::read());

// Reset the PKRU state to what we originally observed.
Expand Down
3 changes: 2 additions & 1 deletion crates/wasmtime/src/config.rs
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Expand Up @@ -2374,7 +2374,8 @@ impl PoolingAllocationConfig {
/// supported
/// - `disable`: never use MPK
///
/// By default this value is `disabled`, but may become `auto` in future releases.
/// By default this value is `disabled`, but may become `auto` in future
/// releases.
///
/// __WARNING__: this configuration options is still experimental--use at
/// your own risk! MPK uses kernel and CPU features to protect memory
Expand Down