[PATCH v3 2/3] hw/gpio/aspeed: Don't let guests modify input pins

[Peter Delevoryas <peter@pjd.dev>]

Up until now, guests could modify input pins by overwriting the data
value register. The guest OS should only be allowed to modify output pin
values, and the QOM property setter should only be permitted to modify
input pins.

This change also updates the gpio input pin test to match this
expectation.

Andrew suggested this particularly refactoring here:

    https://lore.kernel.org/qemu-devel/23523aa1-ba81-412b-92cc-8174faba3612@www.fastmail.com/

Suggested-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Peter Delevoryas <peter@pjd.dev>
Fixes: 4b7f956862dc ("hw/gpio: Add basic Aspeed GPIO model for AST2400 and AST2500")
---
 hw/gpio/aspeed_gpio.c          | 15 ++++++++-------
 tests/qtest/aspeed_gpio-test.c |  2 +-
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/hw/gpio/aspeed_gpio.c b/hw/gpio/aspeed_gpio.c
index a62a673857..1e267dd482 100644
--- a/hw/gpio/aspeed_gpio.c
+++ b/hw/gpio/aspeed_gpio.c
@@ -268,7 +268,7 @@ static ptrdiff_t aspeed_gpio_set_idx(AspeedGPIOState *s, GPIOSets *regs)
 }
 
 static void aspeed_gpio_update(AspeedGPIOState *s, GPIOSets *regs,
-                               uint32_t value)
+                               uint32_t value, uint32_t mode_mask)
 {
     uint32_t input_mask = regs->input_mask;
     uint32_t direction = regs->direction;
@@ -277,7 +277,8 @@ static void aspeed_gpio_update(AspeedGPIOState *s, GPIOSets *regs,
     uint32_t diff;
     int gpio;
 
-    diff = old ^ new;
+    diff = (old ^ new);
+    diff &= mode_mask;
     if (diff) {
         for (gpio = 0; gpio < ASPEED_GPIOS_PER_SET; gpio++) {
             uint32_t mask = 1 << gpio;
@@ -339,7 +340,7 @@ static void aspeed_gpio_set_pin_level(AspeedGPIOState *s, uint32_t set_idx,
         value &= ~pin_mask;
     }
 
-    aspeed_gpio_update(s, &s->sets[set_idx], value);
+    aspeed_gpio_update(s, &s->sets[set_idx], value, ~s->sets[set_idx].direction);
 }
 
 /*
@@ -653,7 +654,7 @@ static void aspeed_gpio_write_index_mode(void *opaque, hwaddr offset,
         reg_value = update_value_control_source(set, set->data_value,
                                                 reg_value);
         set->data_read = reg_value;
-        aspeed_gpio_update(s, set, reg_value);
+        aspeed_gpio_update(s, set, reg_value, set->direction);
         return;
     case gpio_reg_idx_direction:
         reg_value = set->direction;
@@ -753,7 +754,7 @@ static void aspeed_gpio_write_index_mode(void *opaque, hwaddr offset,
             __func__, offset, data, reg_idx_type);
         return;
     }
-    aspeed_gpio_update(s, set, set->data_value);
+    aspeed_gpio_update(s, set, set->data_value, UINT32_MAX);
     return;
 }
 
@@ -799,7 +800,7 @@ static void aspeed_gpio_write(void *opaque, hwaddr offset, uint64_t data,
         data &= props->output;
         data = update_value_control_source(set, set->data_value, data);
         set->data_read = data;
-        aspeed_gpio_update(s, set, data);
+        aspeed_gpio_update(s, set, data, set->direction);
         return;
     case gpio_reg_direction:
         /*
@@ -875,7 +876,7 @@ static void aspeed_gpio_write(void *opaque, hwaddr offset, uint64_t data,
                       PRIx64"\n", __func__, offset);
         return;
     }
-    aspeed_gpio_update(s, set, set->data_value);
+    aspeed_gpio_update(s, set, set->data_value, UINT32_MAX);
     return;
 }
 
diff --git a/tests/qtest/aspeed_gpio-test.c b/tests/qtest/aspeed_gpio-test.c
index 8f52454099..d38f51d719 100644
--- a/tests/qtest/aspeed_gpio-test.c
+++ b/tests/qtest/aspeed_gpio-test.c
@@ -69,7 +69,7 @@ static void test_set_input_pins(const void *data)
 
     qtest_writel(s, AST2600_GPIO_BASE + GPIO_ABCD_DATA_VALUE, 0x00000000);
     value = qtest_readl(s, AST2600_GPIO_BASE + GPIO_ABCD_DATA_VALUE);
-    g_assert_cmphex(value, ==, 0x00000000);
+    g_assert_cmphex(value, ==, 0xffffffff);
 }
 
 int main(int argc, char **argv)
-- 
2.37.0