Stream: git-wasmtime

Topic: wasmtime / issue #9026 Handling pointer provenance in Pulley

Wasmtime GitHub notifications bot (Jul 26 2024 at 19:14):

alexcrichton opened issue #9026:

This started out as https://github.com/bytecodealliance/wasmtime/issues/9015 but I'm evolving this now to be about Pulley specifically. Current thinking is that Pulley will not be compatible with -Zmiri-strict-provenance, but changes are necessary to make it compatible with -Zmiri-permissive-provenance. I believe the concrete of changes are:

• The ptr: *mut u8 field of XRegValUnion must be replaced with a usize value
• The new_ptr constructor will use expose_provenance and load/store usize
• The get_ptr accessor will use with_exposed_provenance with the usize field
• When entering the interpreter Wasmtime will be require to call expose_provenance on any pointers that Pulley may access. This notably affects the VMContext field and any transitive pointers that it contains. This can probably be done during the construction of VMContext itself.

Right now expose_provenance and with_exposed_provenance are unstable so I don't believe that this is actionable at this time, but I wanted to write this down for later.

cc @fitzgen

Wasmtime GitHub notifications bot (Jul 26 2024 at 19:15):

alexcrichton commented on issue #9026:

Ralf also pointed to https://github.com/rust-lang/unsafe-code-guidelines/issues/497 which has some interesting discussion and I believe reaches a similar conclusion.

Wasmtime GitHub notifications bot (Jul 29 2024 at 15:57):

fitzgen commented on issue #9026:

Ralf also pointed to rust-lang/unsafe-code-guidelines#497 which has some interesting discussion and I believe reaches a similar conclusion.

This comment from Ralf, in particular, seems to summarize our recent discussions: https://github.com/rust-lang/unsafe-code-guidelines/issues/497#issuecomment-2003100550

Wasmtime GitHub notifications bot (Jan 13 2025 at 17:47):

alexcrichton added the pulley label to Issue #9026.

Wasmtime GitHub notifications bot (Jan 13 2025 at 17:47):

github-actions[bot] commented on issue #9026:

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cc @fitzgen

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Wasmtime GitHub notifications bot (Jan 24 2025 at 16:13):

alexcrichton closed issue #9026:

This started out as https://github.com/bytecodealliance/wasmtime/issues/9015 but I'm evolving this now to be about Pulley specifically. Current thinking is that Pulley will not be compatible with -Zmiri-strict-provenance, but changes are necessary to make it compatible with -Zmiri-permissive-provenance. I believe the concrete of changes are:

• The ptr: *mut u8 field of XRegValUnion must be replaced with a usize value
• The new_ptr constructor will use expose_provenance and load/store usize
• The get_ptr accessor will use with_exposed_provenance with the usize field
• When entering the interpreter Wasmtime will be require to call expose_provenance on any pointers that Pulley may access. This notably affects the VMContext field and any transitive pointers that it contains. This can probably be done during the construction of VMContext itself.

Right now expose_provenance and with_exposed_provenance are unstable so I don't believe that this is actionable at this time, but I wanted to write this down for later.

cc @fitzgen

Wasmtime GitHub notifications bot (Jan 24 2025 at 16:13):

alexcrichton commented on issue #9026:

This is now resolved with a combination of https://github.com/bytecodealliance/wasmtime/pull/10043 and https://github.com/bytecodealliance/wasmtime/pull/10096

Last updated: Dec 06 2025 at 06:05 UTC