threat-modeling.md

Threat Model Analysis for gfx-rs/gfx

Threat: Shader Injection

• Threat: Shader Injection

  • Description: An attacker provides malicious shader code (GLSL, HLSL, SPIR-V, etc.) to the application. This is possible if the application loads shaders from untrusted sources or fails to properly sanitize them. The attacker could craft a shader to cause a crash, read from unauthorized memory (if the API allows), or perform computationally expensive operations. The success and impact depend heavily on the specific graphics backend and driver, but the entry point is through gfx-rs.
  • Impact: Denial of service (application crash or GPU hang), potential information disclosure (reading from unintended memory), potential arbitrary code execution (rare, but possible with some driver vulnerabilities exploited through the injected shader).
  • Affected Component: gfx_hal::device::Device::create_shader_module, shader loading/compilation pipeline, and the backend-specific shader compiler interaction (e.g., with shaderc for SPIR-V).
  • Risk Severity: High to Critical (depending on the backend and driver vulnerabilities that could be triggered by the shader).
  • Mitigation Strategies:
    • Strict Input Validation: Validate all shader source code against a strict whitelist of allowed operations and data types. Reject any shader with suspicious constructs.
    • Checksums/Digital Signatures: If loading pre-compiled shaders, verify integrity using checksums or digital signatures.
    • Offline Compilation: Compile shaders offline whenever possible, and only load pre-compiled, verified binaries.
    • SPIR-V Validation: If using Vulkan and SPIR-V, always use spirv-val (Vulkan SDK) to validate the generated SPIR-V before passing it to gfx-rs.

Threat: Resource Exhaustion (Texture/Buffer Overflow)

• Threat: Resource Exhaustion (Texture/Buffer Overflow)

  • Description: An attacker provides excessively large texture dimensions, vertex counts, or other resource allocation requests through the gfx-rs API. This causes the application to attempt to allocate an unreasonable amount of GPU memory, leading to a denial of service. The gfx-rs library itself should have some safeguards, but ultimately relies on the application to provide reasonable values.
  • Impact: Denial of service (application crash, GPU hang, potential system-wide instability).
  • Affected Component: gfx_hal::device::Device::create_buffer, gfx_hal::device::Device::create_image, gfx_hal::memory::Requirements, and the memory allocation functions within the chosen gfx-rs backend.
  • Risk Severity: High
  • Mitigation Strategies:
    • Strict Resource Limits: Impose hard limits on the size and number of graphics resources that can be created via the gfx-rs API (e.g., maximum texture dimensions, maximum vertex count). These limits should be enforced before calling gfx-rs functions.
    • Input Validation: Validate all user-provided or externally-sourced data that influences resource allocation (e.g., image dimensions, model complexity) before passing it to gfx-rs.
    • Memory Budget: Implement a memory budget and track memory usage as reported by gfx-rs. Reject allocation requests that would exceed the budget.

Threat: Invalid Command Buffer Manipulation

• Threat: Invalid Command Buffer Manipulation

  • Description: An attacker crafts invalid command buffer submissions through the gfx-rs API. This could involve submitting commands out of order, using invalid resource handles, or violating API constraints. This is more likely if the application has vulnerabilities that allow an attacker to influence the command buffer generation process, but the actual invalid commands are executed via gfx-rs.
  • Impact: Denial of service (application crash or GPU hang), undefined behavior, potentially leading to data corruption or information disclosure (depending on the specific API violation and the backend's handling of it).
  • Affected Component: gfx_hal::command::CommandBuffer, gfx_hal::queue::Queue::submit, and the command buffer recording and submission functions within gfx-rs.
  • Risk Severity: High
  • Mitigation Strategies:
    • Robust API Usage: Carefully follow the gfx-rs API documentation and best practices for command buffer creation and submission. This is the primary defense.
    • Validation Layers (Vulkan): When using Vulkan, always enable the validation layers during development. These layers can catch many common errors in gfx-rs API usage before they reach the driver.
    • Input Validation: If any external data influences the command buffer generation (e.g., user input controlling rendering parameters), thoroughly validate that data before using it to construct gfx-rs commands.
    • Error Handling: Implement robust error handling for all gfx-rs API calls, especially those related to command buffer submission. Do not continue rendering if an error is reported by gfx-rs.

Threat: Integer Overflow/Underflow in Resource Calculations Passed to gfx-rs

• Threat: Integer Overflow/Underflow in Resource Calculations Passed to gfx-rs

  • Description: The application performs calculations to determine resource sizes (e.g., buffer sizes, texture dimensions). If these calculations are susceptible to integer overflows or underflows, and the resulting incorrect values are passed to gfx-rs, it could lead to incorrect memory allocation or access within gfx-rs or the underlying backend, potentially causing crashes or vulnerabilities. The vulnerability originates in the application code, but manifests through gfx-rs.
  • Impact: Denial of service (crash), potential memory corruption within gfx-rs or the backend, potential arbitrary code execution (rare, but possible depending on the backend).
  • Affected Component: Application code that calculates resource sizes, specifically the values passed to gfx_hal::memory::Requirements and resource creation functions like create_buffer and create_image.
  • Risk Severity: High
  • Mitigation Strategies:
    • Checked Arithmetic: Use checked arithmetic operations (e.g., Rust's checked_add, checked_mul) to detect and handle overflows/underflows before passing values to gfx-rs.
    • Input Validation: Validate all input values that are used in resource size calculations to ensure they are within reasonable bounds before using them in calculations passed to gfx-rs.
    • Saturating Arithmetic: Consider using saturating arithmetic (e.g., Rust's saturating_add, saturating_mul) as an alternative, if appropriate, to prevent unexpected values from being passed to gfx-rs.