59 lines
2.0 KiB
Markdown
59 lines
2.0 KiB
Markdown
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# Metal Shader Security Tests (Issue #57)
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## Bounds Checking Verification
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This document describes the security fixes applied to `ggml-metal-turbo.metal` and how to verify them.
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## Changes Made
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### 1. `kernel_fwht_128`
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- **Before:** No bounds checking on `tid`
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- **After:** Added `n_elements` parameter, early exit if `tid >= n_elements`
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- **Impact:** Prevents GPU out-of-bounds reads when grid size exceeds data elements
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### 2. `kernel_turbo4_dequant`
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- **Before:** No validation of `src` or `norms` buffer sizes
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- **After:** Added `src_size` and `norms_size` parameters, validates all buffer accesses
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- **Impact:** Prevents reading beyond allocated buffers
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### 3. `kernel_attention_turbo4`
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- **Before:** Empty body (incomplete implementation)
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- **After:** Fully implemented with bounds checking for Q, K, and scores buffers
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- **Impact:** Proper attention computation with security guarantees
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### 4. `kernel_softmax` (new)
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- Added softmax kernel for attention pipeline
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- Includes bounds checking for row/column indices
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## Testing
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### Manual Testing (Metal)
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```metal
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// Test with oversized grid
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MTLSize grid = MTLSizeMake(1000, 1, 1); // More threads than elements
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[encoder dispatchThreads:grid threadsPerThreadgroup:MTLSizeMake(128, 1, 1)];
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```
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### Validation Checklist
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- [ ] `kernel_fwht_128`: Threads beyond `n_elements` return immediately
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- [ ] `kernel_turbo4_dequant`: Buffer sizes validated before access
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- [ ] `kernel_attention_turbo4`: All buffer accesses bounded
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- [ ] `kernel_softmax`: Row index validated
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- [ ] No GPU crashes with oversized dispatch grids
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- [ ] No memory leaks from OOB reads
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## Performance Impact
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Bounds checking adds minimal overhead:
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- One comparison per thread (negligible)
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- Early exit saves computation for invalid threads
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- No impact on valid (within-bounds) execution paths
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## Security Assessment
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**Before:** Medium risk — GPU OOB reads could leak memory or crash
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**After:** Low risk — All buffer accesses validated
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**Severity:** Medium → Low
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