Re: [PATCH] hw/gpio/aspeed: Add bounds checking for register table access

[Andrew Jeffery <andrew@codeconstruct.com.au>]

Hello Zheyu Ma,

On Tue, 2024-06-18 at 15:09 +0200, Zheyu Ma wrote:
> Added bounds checking in the aspeed_gpio_read() and aspeed_gpio_write()
> functions to ensure the index idx is within the valid range of the
> reg_table array.
> 
> The correct size of reg_table is determined dynamically based on whether
> it is aspeed_3_3v_gpios or aspeed_1_8v_gpios. If idx exceeds the
> size of reg_table, an error is logged, and the function returns.
> 
> AddressSanitizer log indicating the issue:
> 
> ==2602930==ERROR: AddressSanitizer: global-buffer-overflow on address 0x55a5da29e128 at pc 0x55a5d700dc62 bp 0x7fff096c4e90 sp 0x7fff096c4e88
> READ of size 2 at 0x55a5da29e128 thread T0
>     #0 0x55a5d700dc61 in aspeed_gpio_read hw/gpio/aspeed_gpio.c:564:14
>     #1 0x55a5d933f3ab in memory_region_read_accessor system/memory.c:445:11
>     #2 0x55a5d92fba40 in access_with_adjusted_size system/memory.c:573:18
>     #3 0x55a5d92f842c in memory_region_dispatch_read1 system/memory.c:1426:16
>     #4 0x55a5d92f7b68 in memory_region_dispatch_read system/memory.c:1459:9
>     #5 0x55a5d9376ad1 in flatview_read_continue_step system/physmem.c:2836:18
>     #6 0x55a5d9376399 in flatview_read_continue system/physmem.c:2877:19
>     #7 0x55a5d93775b8 in flatview_read system/physmem.c:2907:12

I'm mildly interested in what you were doing to trigger this. Certainly
we could do with a guard in the model to prevent it, but I'm curious
all the same.

> 
> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
> ---
>  hw/gpio/aspeed_gpio.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/hw/gpio/aspeed_gpio.c b/hw/gpio/aspeed_gpio.c
> index c1781e2ba3..1441046f6c 100644
> --- a/hw/gpio/aspeed_gpio.c
> +++ b/hw/gpio/aspeed_gpio.c
> @@ -550,6 +550,7 @@ static uint64_t aspeed_gpio_read(void *opaque, hwaddr offset, uint32_t size)
>      GPIOSets *set;
>      uint32_t value = 0;
>      uint64_t debounce_value;
> +    uint32_t reg_table_size;
>  
>      idx = offset >> 2;
>      if (idx >= GPIO_DEBOUNCE_TIME_1 && idx <= GPIO_DEBOUNCE_TIME_3) {
> @@ -559,6 +560,18 @@ static uint64_t aspeed_gpio_read(void *opaque, hwaddr offset, uint32_t size)
>          return debounce_value;
>      }
>  
> +    if (agc->reg_table == aspeed_3_3v_gpios) {
> +        reg_table_size = GPIO_3_3V_REG_ARRAY_SIZE;
> +    } else {
> +        reg_table_size = GPIO_1_8V_REG_ARRAY_SIZE;
> +    }

I think I'd prefer we add reg_table_size as a member of AspeedGPIOClass
and initialise it at the same time as we initialise reg_table. I feel
it would help maintain safety in the face of future changes (i.e. if
another reg table were introduced). With that approach the hunk above
can be dropped.

> +
> +    if (idx >= reg_table_size) {

This condition would then become:

```
if (idx >= agc->reg_table_size) {
```

Thoughts?

Andrew