Fix out-of-bounds memory access in Galore dequant kernel (#1125)

Author: gau-nernst

torchao/prototype/galore/kernels/quant.py

@@ -11,6 +11,8 @@ def _dequant_kernel(
     dq_ptr,
     stride_qm,
     stride_qn,
+    M,
+    N,
     GROUP_SIZE: tl.constexpr,
     BLOCK_M: tl.constexpr,
     BLOCK_N: tl.constexpr,
@@ -22,17 +24,18 @@ def _dequant_kernel(
     # rm = tl.max_contiguous(tl.multiple_of(rm % M, BLOCK_M), BLOCK_M)
     # rn = tl.max_contiguous(tl.multiple_of(rn % N, BLOCK_N), BLOCK_N)
     offsets = rm[:, None] * stride_qm + rn[None, :] * stride_qn
+    mask = (rm[:, None] < M) & (rn[None, :] < N)
     tl.static_print(offsets)
     group_offsets = offsets // GROUP_SIZE
     tl.static_print("group_offsets", group_offsets)
-    q_idx = tl.load(q_idx_ptr + offsets)
+    q_idx = tl.load(q_idx_ptr + offsets, mask=mask)
     tl.static_print(q_idx)
     # NOTE: Must upcast q_idx to int32 (q_idx is tl.uint8, which does not work for pointer indexing)
     q_vals = tl.load(qmap_ptr + q_idx.to(tl.int32))
-    absmax = tl.load(absmax_ptr + group_offsets)
+    absmax = tl.load(absmax_ptr + group_offsets, mask=group_offsets < (M * N // GROUP_SIZE))
 
     dq = q_vals * absmax
-    tl.store(dq_ptr + offsets, dq)
+    tl.store(dq_ptr + offsets, dq, mask=mask)
 
 
 def triton_dequant_blockwise(
@@ -51,6 +54,8 @@ def triton_dequant_blockwise(
         dq,
         q.stride(0),
         q.stride(1),
+        M,
+        N,
         BLOCK_M=1,
         BLOCK_N=group_size,
         GROUP_SIZE=group_size,