Re: [PATCH v2] drm/amd/display: Fix potential null pointer dereference in dc_dmub_srv

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Reviewed-by: Tom Chung <chiahsuan.chung@xxxxxxx>

On 2/20/2024 5:06 PM, Srinivasan Shanmugam wrote:
Fixes potential null pointer dereference warnings in the
dc_dmub_srv_cmd_list_queue_execute() and dc_dmub_srv_is_hw_pwr_up()

In both functions, the 'dc_dmub_srv' variable was being dereferenced
before it was checked for null. This could lead to a null pointer
dereference if 'dc_dmub_srv' is null. The fix is to check if
'dc_dmub_srv' is null before dereferencing it.

Thus moving the null checks for 'dc_dmub_srv' to the beginning of the
functions to ensure that 'dc_dmub_srv' is not null when it is

Found by smatch & thus fixing the below:
drivers/gpu/drm/amd/amdgpu/../display/dc/dc_dmub_srv.c:133 dc_dmub_srv_cmd_list_queue_execute() warn: variable dereferenced before check 'dc_dmub_srv' (see line 128)
drivers/gpu/drm/amd/amdgpu/../display/dc/dc_dmub_srv.c:1167 dc_dmub_srv_is_hw_pwr_up() warn: variable dereferenced before check 'dc_dmub_srv' (see line 1164)

Fixes: 01fbdc34c687 ("drm/amd/display: decouple dmcub execution to reduce lock granularity")
Fixes: 65138eb72e1f ("drm/amd/display: Add DCN35 DMUB")
Cc: JinZe.Xu <jinze.xu@xxxxxxx>
Cc: Hersen Wu <hersenxs.wu@xxxxxxx>
Cc: Josip Pavic <josip.pavic@xxxxxxx>
Cc: Roman Li <>
Cc: Qingqing Zhuo <Qingqing.Zhuo@xxxxxxx>
Cc: Harry Wentland <Harry.Wentland@xxxxxxx>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@xxxxxxx>
Cc: Aurabindo Pillai <aurabindo.pillai@xxxxxxx>
Cc: Tom Chung <chiahsuan.chung@xxxxxxx>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@xxxxxxx>
  - For dc_dmub_srv_is_hw_pwr_up() move 'dc_ctx = dc_dmub_srv->ctx;'
    below 'if (dc_dmub_srv->ctx->dc->debug.dmcub_emulation)' (Tom)

  drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c | 7 +++++--
  1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c b/drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c
index 0bc32537e2eb..a115e1170ef5 100644
--- a/drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c
+++ b/drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c
@@ -128,7 +128,7 @@ bool dc_dmub_srv_cmd_list_queue_execute(struct dc_dmub_srv *dc_dmub_srv,
  		unsigned int count,
  		union dmub_rb_cmd *cmd_list)
-	struct dc_context *dc_ctx = dc_dmub_srv->ctx;
+	struct dc_context *dc_ctx;
  	struct dmub_srv *dmub;
  	enum dmub_status status;
  	int i;
@@ -136,6 +136,7 @@ bool dc_dmub_srv_cmd_list_queue_execute(struct dc_dmub_srv *dc_dmub_srv,
  	if (!dc_dmub_srv || !dc_dmub_srv->dmub)
  		return false;
+ dc_ctx = dc_dmub_srv->ctx;
  	dmub = dc_dmub_srv->dmub;
for (i = 0 ; i < count; i++) {
@@ -1169,7 +1170,7 @@ void dc_dmub_srv_subvp_save_surf_addr(const struct dc_dmub_srv *dc_dmub_srv, con
bool dc_dmub_srv_is_hw_pwr_up(struct dc_dmub_srv *dc_dmub_srv, bool wait)
-	struct dc_context *dc_ctx = dc_dmub_srv->ctx;
+	struct dc_context *dc_ctx;
  	enum dmub_status status;
if (!dc_dmub_srv || !dc_dmub_srv->dmub)
@@ -1177,6 +1178,8 @@ bool dc_dmub_srv_is_hw_pwr_up(struct dc_dmub_srv *dc_dmub_srv, bool wait)
if (dc_dmub_srv->ctx->dc->debug.dmcub_emulation)
  		return true;
+	dc_ctx = dc_dmub_srv->ctx;
if (wait) {
  		if (dc_dmub_srv->ctx->dc->debug.disable_timeout) {

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