[coreboot-gerrit] Change in coreboot[master]: soc/intel/baytrail: Prevent unintended sign extensions

[Patrick Georgi (Code Review)]

Patrick Georgi has submitted this change and it was merged. ( https://review.coreboot.org/c/coreboot/+/34487 )

Change subject: soc/intel/baytrail: Prevent unintended sign extensions
......................................................................

soc/intel/baytrail: Prevent unintended sign extensions

Consider the following assignment:

u64 = s32

For positive values this is fine, but if the s32 is negative, it will be
sign-extended in the conversion to a very large unsigned integer. This
manifests itself in two ways in the following code:

First, gpu_pipe{a,b}_port_select are defined as int, and can have the
values 1 or 2. In the case when they have the value 2, the shift 2 << 30
will be a negative number, making it susceptible to the sign-extension
problem above. Change these variables to something more reasonable like
a uint8_t, which is unsigned.

Second, in any bit shift, any variable with width less than an int will
be implicitly promoted to an int before performing the bit shift.
For example, the variable gpu_pipea_power_on_delay is a uint16_t, and if its
highest bit is set, the shift gpu_pipea_power_on_delay << 16 will become
negative, again introducing the above problem. To prevent this, cast all
smaller variables to a u32 before the shift, which will prevent the
implicit promotions and sign extensions.

Change-Id: Ic5db6001504cefb501dee199590a0e961a15771b
Signed-off-by: Jacob Garber 
Found-by: Coverity CID 1229699, 1229700, 1229701, 1229702
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34487
Reviewed-by: Angel Pons 
Reviewed-by: Alexander Couzens 
Tested-by: build bot (Jenkins) 
---
M src/soc/intel/baytrail/chip.h
M src/soc/intel/baytrail/gfx.c
2 files changed, 12 insertions(+), 12 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Alexander Couzens: Looks good to me, approved
  Angel Pons: Looks good to me, approved

diff --git a/src/soc/intel/baytrail/chip.h b/src/soc/intel/baytrail/chip.h
index 7736e72..00e7fd6 100644
--- a/src/soc/intel/baytrail/chip.h
+++ b/src/soc/intel/baytrail/chip.h
@@ -69,7 +69,7 @@
    /* Allow PCIe devices to wake system from suspend. */
    int pcie_wake_enable;

-	int gpu_pipea_port_select;	/* Port select: 1=DP_B 2=DP_C */
+	uint8_t gpu_pipea_port_select;	/* Port select: 1=DP_B 2=DP_C */
    uint16_t gpu_pipea_power_on_delay;
    uint16_t gpu_pipea_light_on_delay;
    uint16_t gpu_pipea_power_off_delay;
@@ -77,7 +77,7 @@
    uint16_t gpu_pipea_power_cycle_delay;
    int gpu_pipea_pwm_freq_hz;

-	int gpu_pipeb_port_select;	/* Port select: 1=DP_B 2=DP_C */
+	uint8_t gpu_pipeb_port_select;	/* Port select: 1=DP_B 2=DP_C */
    uint16_t gpu_pipeb_power_on_delay;
    uint16_t gpu_pipeb_light_on_delay;
    uint16_t gpu_pipeb_power_off_delay;
diff --git a/src/soc/intel/baytrail/gfx.c b/src/soc/intel/baytrail/gfx.c
index 4a79991..5100c8e 100644
--- a/src/soc/intel/baytrail/gfx.c
+++ b/src/soc/intel/baytrail/gfx.c
@@ -320,13 +320,13 @@
    			PP_CONTROL_UNLOCK | PP_CONTROL_EDP_FORCE_VDD),
    	/* POWER ON */
    	REG_RES_WRITE32(PCI_BASE_ADDRESS_0, PIPEA_REG(PP_ON_DELAYS),
-				(config->gpu_pipea_port_select << 30 |
-				 config->gpu_pipea_power_on_delay << 16 |
-				 config->gpu_pipea_light_on_delay)),
+				((u32)config->gpu_pipea_port_select << 30 |
+				 (u32)config->gpu_pipea_power_on_delay << 16 |
+				 (u32)config->gpu_pipea_light_on_delay)),
    	/* POWER OFF */
    	REG_RES_WRITE32(PCI_BASE_ADDRESS_0, PIPEA_REG(PP_OFF_DELAYS),
-				(config->gpu_pipea_power_off_delay << 16 |
-				 config->gpu_pipea_light_off_delay)),
+				((u32)config->gpu_pipea_power_off_delay << 16 |
+				 (u32)config->gpu_pipea_light_off_delay)),
    	/* DIVISOR */
    	REG_RES_RMW32(PCI_BASE_ADDRESS_0, PIPEA_REG(PP_DIVISOR),
    		      ~0x1f, config->gpu_pipea_power_cycle_delay),
@@ -338,13 +338,13 @@
    			PP_CONTROL_UNLOCK | PP_CONTROL_EDP_FORCE_VDD),
    	/* POWER ON */
    	REG_RES_WRITE32(PCI_BASE_ADDRESS_0, PIPEB_REG(PP_ON_DELAYS),
-				(config->gpu_pipeb_port_select << 30 |
-				 config->gpu_pipeb_power_on_delay << 16 |
-				 config->gpu_pipeb_light_on_delay)),
+				((u32)config->gpu_pipeb_port_select << 30 |
+				 (u32)config->gpu_pipeb_power_on_delay << 16 |
+				 (u32)config->gpu_pipeb_light_on_delay)),
    	/* POWER OFF */
    	REG_RES_WRITE32(PCI_BASE_ADDRESS_0, PIPEB_REG(PP_OFF_DELAYS),
-				(config->gpu_pipeb_power_off_delay << 16 |
-				 config->gpu_pipeb_light_off_delay)),
+				((u32)config->gpu_pipeb_power_off_delay << 16 |
+				 (u32)config->gpu_pipeb_light_off_delay)),
    	/* DIVISOR */
    	REG_RES_RMW32(PCI_BASE_ADDRESS_0, PIPEB_REG(PP_DIVISOR),
    		      ~0x1f, config->gpu_pipeb_power_cycle_delay),