[PATCH] drm/amdgpu: check ras and obj before dereference

[Dmitriy Chumachenko]

nbio_v7_9_handle_ras_controller_intr_no_bifring() dereferences ras and obj
without checking either for NULL. Both amdgpu_ras_get_context() and 
amdgpu_ras_find_obj() can return NULL, e.g. during the window between 
adev->nbio.ras being set (early in amdgpu_ras_init(), by design, to 
enable the fatal-error interrupt as soon as possible) and the PCIE_BIF 
ras object actually being created in RAS late_init. Any interrupt in that 
window crashes in hard-IRQ context.

This is analogous to commit d190b459b2a4 ("drm/amdgpu: the warning
dereferencing obj for nbio_v7_4"), which fixed the same issue in the
nbio_v7_4 handler.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 7692e1ee2446 ("drm/amdgpu: add RAS fatal error handler for NBIO v7.9")
Signed-off-by: Dmitriy Chumachenko <Dmitry.Chumachenko@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/amd/amdgpu/nbio_v7_9.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/nbio_v7_9.c b/drivers/gpu/drm/amd/amdgpu/nbio_v7_9.c
index 8e401f8b2a05..2b3a1b9f8efc 100644
--- a/drivers/gpu/drm/amd/amdgpu/nbio_v7_9.c
+++ b/drivers/gpu/drm/amd/amdgpu/nbio_v7_9.c
@@ -518,7 +518,7 @@ static void nbio_v7_9_handle_ras_controller_intr_no_bifring(struct amdgpu_device
 						RAS_CNTLR_INTERRUPT_CLEAR, 1);
 		WREG32_SOC15(NBIO, 0, regBIF_BX0_BIF_DOORBELL_INT_CNTL, bif_doorbell_intr_cntl);
 
-		if (!ras->disable_ras_err_cnt_harvest) {
+		if (ras && !ras->disable_ras_err_cnt_harvest && obj) {
 			/*
 			 * clear error status after ras_controller_intr
 			 * according to hw team and count ue number
-- 
2.49.0