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Miscompilation of `i8x16.swizzle` and `select` with v128 inputs

Moderate severity GitHub Reviewed Published Jun 27, 2022 in bytecodealliance/wasmtime • Updated Mar 14, 2024

Package

cargo cranelift-codegen (Rust)

Affected versions

< 0.85.1

Patched versions

0.85.1
cargo wasmtime (Rust)
< 0.38.1
0.38.1

Description

Impact

Wasmtime's implementation of the SIMD proposal for WebAssembly on x86_64 contained two distinct bugs in the instruction lowerings implemented in Cranelift. The aarch64 implementation of the simd proposal is not affected. The bugs were presented in the i8x16.swizzle and select WebAssembly instructions. The select instruction is only affected when the inputs are of v128 type. The correspondingly affected Cranelift instructions were swizzle and select.

The swizzle instruction lowering in Cranelift erroneously overwrote the mask input register which could corrupt a constant value, for example. This means that future uses of the same constant may see a different value than the constant itself.

The select instruction lowering in Cranelift wasn't correctly implemented for vector types that are 128-bits wide. When the condition was 0 the wrong instruction was used to move the correct input to the output of the instruction meaning that only the low 32 bits were moved and the upper 96 bits of the result were left as whatever the register previously contained (instead of the input being moved from). The select instruction worked correctly if the condition was nonzero, however.

This bug in Wasmtime's implementation of these instructions on x86_64 represents an incorrect implementation of the specified semantics of these instructions according to the WebAssembly specification. The impact of this is benign for hosts running WebAssembly but represents possible vulnerabilities within the execution of a guest program. For example a WebAssembly program could take unintended branches or materialize incorrect values internally which runs the risk of exposing the program itself to other related vulnerabilities which can occur from miscompilations.

Patches

We have released Wasmtime 0.38.1 and cranelift-codegen (and other associated cranelift crates) 0.85.1 which contain the corrected implementations of these two instructions in Cranelift.

Workarounds

If upgrading is not an option for you at this time, you can avoid the vulnerability by disabling the Wasm simd proposal

config.wasm_simd(false);

Additionally the bug is only present on x86_64 hosts. Other aarch64 hosts are not affected. Note that s390x hosts don't yet implement the simd proposal and are not affected.

References

For more information

If you have any questions or comments about this advisory:

References

@alexcrichton alexcrichton published to bytecodealliance/wasmtime Jun 27, 2022
Published by the National Vulnerability Database Jun 28, 2022
Published to the GitHub Advisory Database Jun 29, 2022
Reviewed Jun 29, 2022
Last updated Mar 14, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L

EPSS score

0.299%
(70th percentile)

Weaknesses

CVE ID

CVE-2022-31104

GHSA ID

GHSA-jqwc-c49r-4w2x

Credits

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