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This commit is contained in:
Chris Fallin
2022-02-02 10:03:31 -08:00
parent 84a8368e88
commit 94410a8d4b
1 changed files with 27 additions and 18 deletions
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45
crates/runtime/src/memfd.rs
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@@ -402,21 +402,30 @@ impl MemFdSlot {
//
// We map these inaccessible at first then mprotect() the
// whole of the initial heap size to R+W below.
//
// Special case: we can skip if the last instantiation had no
// image. This means that the whole slot is filled with an
// anonymous mmap backing (and it will have already been
// cleared by the madvise). We may however need to
// mprotect(NONE) the space above `initial_size_bytes` if the
// last use of this slot left it larger. This also lets us
// skip an mmap the first time a MemFdSlot is used, because we
// require the caller to give us a fixed address in an
// already-mmaped-with-anon-memory region. This is important
// for the on-demand allocator.
if self.image.is_some() {
self.map_anon_memory(rustix::io::ProtFlags::empty())
self.reset_with_anon_memory()
.map_err(|e| InstantiationError::Resource(e.into()))?;
} else if initial_size_bytes < self.initial_size {
// Special case: we can skip if the last instantiation had
// no image. This means that the whole slot is filled with
// an anonymous mmap backing (and it will have already
// been cleared by the madvise). We may however need to
// mprotect(NONE) the space above `initial_size_bytes` if
// the last use of this slot left it larger. This also
// lets us skip an mmap the first time a MemFdSlot is
// used, because we require the caller to give us a fixed
// address in an already-mmaped-with-anon-memory
// region. This is important for the on-demand allocator.
//
// So we come in with:
// - anon-zero memory, R+W, [0, self.initial_size)
// - anon-zero memory, none, [self.initial_size, self.static_size)
// and we want:
// - anon-zero memory, R+W, [0, initial_size_bytes)
// - anon-zero memory, none, [initial_size_bytes, self.static_size)
//
// so given initial_size_bytes < self.initial_size we
// mprotect(NONE) the zone from the first to the second.
self.set_protection(
initial_size_bytes,
self.initial_size,
@@ -428,6 +437,7 @@ impl MemFdSlot {
// The initial memory image, if given. If not, we just get a
// memory filled with zeroes.
if let Some(image) = maybe_image {
assert!(image.offset.checked_add(image.len).unwrap() <= initial_size_bytes);
if image.len > 0 {
let image = image.clone();
@@ -510,15 +520,14 @@ impl MemFdSlot {
self.dirty
}
/// Map anonymous zeroed memory across the whole slot, with the
/// given protections. Used both during instantiate and during
/// drop.
fn map_anon_memory(&self, prot: rustix::io::ProtFlags) -> Result<()> {
/// Map anonymous zeroed memory across the whole slot,
/// inaccessible. Used both during instantiate and during drop.
fn reset_with_anon_memory(&self) -> Result<()> {
unsafe {
let ptr = rustix::io::mmap_anonymous(
self.base as *mut c_void,
self.static_size,
prot,
rustix::io::ProtFlags::empty(),
rustix::io::MapFlags::PRIVATE | rustix::io::MapFlags::FIXED,
)?;
assert_eq!(ptr as usize, self.base);
@@ -560,7 +569,7 @@ impl Drop for MemFdSlot {
// this MemFdSlot has indicated that it will clean up in some
// other way.
if self.clear_on_drop {
let _ = self.map_anon_memory(rustix::io::ProtFlags::empty());
let _ = self.reset_with_anon_memory();
}
}
}