* Add guard pages to the front of linear memories
This commit implements a safety feature for Wasmtime to place guard
pages before the allocation of all linear memories. Guard pages placed
after linear memories are typically present for performance (at least)
because it can help elide bounds checks. Guard pages before a linear
memory, however, are never strictly needed for performance or features.
The intention of a preceding guard page is to help insulate against bugs
in Cranelift or other code generators, such as CVE-2021-32629.
This commit adds a `Config::guard_before_linear_memory` configuration
option, defaulting to `true`, which indicates whether guard pages should
be present both before linear memories as well as afterwards. Guard
regions continue to be controlled by
`{static,dynamic}_memory_guard_size` methods.
The implementation here affects both on-demand allocated memories as
well as the pooling allocator for memories. For on-demand memories this
adjusts the size of the allocation as well as adjusts the calculations
for the base pointer of the wasm memory. For the pooling allocator this
will place a singular extra guard region at the very start of the
allocation for memories. Since linear memories in the pooling allocator
are contiguous every memory already had a preceding guard region in
memory, it was just the previous memory's guard region afterwards. Only
the first memory needed this extra guard.
I've attempted to write some tests to help test all this, but this is
all somewhat tricky to test because the settings are pretty far away
from the actual behavior. I think, though, that the tests added here
should help cover various use cases and help us have confidence in
tweaking the various `Config` settings beyond their defaults.
Note that this also contains a semantic change where
`InstanceLimits::memory_reservation_size` has been removed. Instead this
field is now inferred from the `static_memory_maximum_size` and guard
size settings. This should hopefully remove some duplication in these
settings, canonicalizing on the guard-size/static-size settings as the
way to control memory sizes and virtual reservations.
* Update config docs
* Fix a typo
* Fix benchmark
* Fix wasmtime-runtime tests
* Fix some more tests
* Try to fix uffd failing test
* Review items
* Tweak 32-bit defaults
Makes the pooling allocator a bit more reasonable by default on 32-bit
with these settings.
Implement Wasmtime's new API as designed by RFC 11. This is quite a large commit which has had lots of discussion externally, so for more information it's best to read the RFC thread and the PR thread.
* wasmtime-wasi: re-exporting this WasiCtxBuilder was shadowing the right one
wasi-common's WasiCtxBuilder is really only useful wasi_cap_std_sync and
wasi_tokio to implement their own Builder on top of.
This re-export of wasi-common's is 1. not useful and 2. shadow's the
re-export of the right one in sync::*.
* wasi-common: eliminate WasiCtxBuilder, make the builder methods on WasiCtx instead
* delete wasi-common::WasiCtxBuilder altogether
just put those methods directly on &mut WasiCtx.
As a bonus, the sync and tokio WasiCtxBuilder::build functions
are no longer fallible!
* bench fixes
* more test fixes
This adds benchmarks around module instantiation using criterion.
Both the default (i.e. on-demand) and pooling allocators are tested
sequentially and in parallel using a thread pool.
Instantiation is tested with an empty module, a module with a single page
linear memory, a larger linear memory with a data initializer, and a "hello
world" Rust WASI program.
Alex Crichton
Pat Hickey
Pat Hickey
Peter Huene