drm/amdgpu/sdma4: replace BUG_ON with WARN_ON in fence emission

commit 78d2e62 upstream.

sdma_v4_0_ring_emit_fence() contains two BUG_ON(addr & 0x3) assertions
that verify fence writeback addresses are dword-aligned.  These
assertions can be reached from unprivileged userspace via crafted
DRM_IOCTL_AMDGPU_CS submissions, causing a fatal kernel panic in a
scheduler worker thread.

Replace both BUG_ON() calls with WARN_ON() to log the condition without
crashing the kernel.  A misaligned fence address at this point indicates
a driver bug, but crashing the kernel is never the correct response when
the assertion is reachable from userspace.

The CS IOCTL path is the correct place to filter invalid submissions;
the ring emission callback is too late to do anything about it.

Fixes: 2130f89 ("drm/amdgpu: add SDMA v4.0 implementation (v2)")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: John B. Moore <jbmoore61@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit b90250b)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: jbmoore61

drivers/gpu/drm/amd/amdgpu/sdma_v4_0.c

@@ -890,7 +890,7 @@ static void sdma_v4_0_ring_emit_fence(struct amdgpu_ring *ring, u64 addr, u64 se
 	/* write the fence */
 	amdgpu_ring_write(ring, SDMA_PKT_HEADER_OP(SDMA_OP_FENCE));
 	/* zero in first two bits */
-	BUG_ON(addr & 0x3);
+	WARN_ON(addr & 0x3);
 	amdgpu_ring_write(ring, lower_32_bits(addr));
 	amdgpu_ring_write(ring, upper_32_bits(addr));
 	amdgpu_ring_write(ring, lower_32_bits(seq));
@@ -900,7 +900,7 @@ static void sdma_v4_0_ring_emit_fence(struct amdgpu_ring *ring, u64 addr, u64 se
 		addr += 4;
 		amdgpu_ring_write(ring, SDMA_PKT_HEADER_OP(SDMA_OP_FENCE));
 		/* zero in first two bits */
-		BUG_ON(addr & 0x3);
+		WARN_ON(addr & 0x3);
 		amdgpu_ring_write(ring, lower_32_bits(addr));
 		amdgpu_ring_write(ring, upper_32_bits(addr));
 		amdgpu_ring_write(ring, upper_32_bits(seq));