drm/amd/pm: Fix out-of-bounds bug

Create new structure SISLANDS_SMC_SWSTATE_SINGLE, as initialState.levels
and ACPIState.levels are never actually used as flexible arrays. Those
arrays can be used as simple objects of type
SISLANDS_SMC_HW_PERFORMANCE_LEVEL, instead.

Currently, the code fails because flexible array _levels_ in
struct SISLANDS_SMC_SWSTATE doesn't allow for code that accesses
the first element of initialState.levels and ACPIState.levels
arrays:

drivers/gpu/drm/amd/pm/powerplay/si_dpm.c:
4820: table->initialState.levels[0].mclk.vDLL_CNTL =
4821:         cpu_to_be32(si_pi->clock_registers.dll_cntl);
...
5021: table->ACPIState.levels[0].mclk.vDLL_CNTL =
5022:         cpu_to_be32(dll_cntl);

because such element cannot be accessed without previously allocating
enough dynamic memory for it to exist (which never actually happens).
So, there is an out-of-bounds bug in this case.

That's why struct SISLANDS_SMC_SWSTATE should only be used as type
for object driverState and new struct SISLANDS_SMC_SWSTATE_SINGLE is
created as type for objects initialState, ACPIState and ULVState.

Also, with the change from one-element array to flexible-array member
in commit 0e1aa13c ("drm/amd/pm: Replace one-element array with
flexible-array in struct SISLANDS_SMC_SWSTATE"), the size of
dpmLevels in struct SISLANDS_SMC_STATETABLE should be fixed to be
SISLANDS_MAX_SMC_PERFORMANCE_LEVELS_PER_SWSTATE instead of
SISLANDS_MAX_SMC_PERFORMANCE_LEVELS_PER_SWSTATE - 1.

Fixes: 0e1aa13c ("drm/amd/pm: Replace one-element array with flexible-array in struct SISLANDS_SMC_SWSTATE")
Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/powerplay/sislands_smc.h

@@ -191,6 +191,14 @@ struct SISLANDS_SMC_SWSTATE
 
 typedef struct SISLANDS_SMC_SWSTATE SISLANDS_SMC_SWSTATE;
 
+struct SISLANDS_SMC_SWSTATE_SINGLE {
+	uint8_t                             flags;
+	uint8_t                             levelCount;
+	uint8_t                             padding2;
+	uint8_t                             padding3;
+	SISLANDS_SMC_HW_PERFORMANCE_LEVEL   level;
+};
+
 #define SISLANDS_SMC_VOLTAGEMASK_VDDC  0
 #define SISLANDS_SMC_VOLTAGEMASK_MVDD  1
 #define SISLANDS_SMC_VOLTAGEMASK_VDDCI 2
@@ -216,11 +224,11 @@ struct SISLANDS_SMC_STATETABLE
 	SISLANDS_SMC_VOLTAGEMASKTABLE		voltageMaskTable;
 	SISLANDS_SMC_VOLTAGEMASKTABLE		phaseMaskTable;
 	PP_SIslands_DPM2Parameters		dpm2Params;
-    SISLANDS_SMC_SWSTATE                initialState;
-    SISLANDS_SMC_SWSTATE                ACPIState;
-    SISLANDS_SMC_SWSTATE                ULVState;
+	struct SISLANDS_SMC_SWSTATE_SINGLE	initialState;
+	struct SISLANDS_SMC_SWSTATE_SINGLE	ACPIState;
+	struct SISLANDS_SMC_SWSTATE_SINGLE	ULVState;
 	SISLANDS_SMC_SWSTATE			driverState;
-    SISLANDS_SMC_HW_PERFORMANCE_LEVEL   dpmLevels[SISLANDS_MAX_SMC_PERFORMANCE_LEVELS_PER_SWSTATE - 1];
+	SISLANDS_SMC_HW_PERFORMANCE_LEVEL	dpmLevels[SISLANDS_MAX_SMC_PERFORMANCE_LEVELS_PER_SWSTATE];
 };
 
 typedef struct SISLANDS_SMC_STATETABLE SISLANDS_SMC_STATETABLE;