Re: [PATCH v2] MIPS: Loongson64: env: Check UARTs passed by LEFI cautiously

[Jiaxun Yang]

On Sun, 15 Mar 2026, at 5:28 PM, Rong Zhang wrote:
> Some firmware does not set nr_uarts properly and passes empty items.
> Iterate at most min(system->nr_uarts, MAX_UARTS) items to prevent
> out-of-bounds access, and ignore UARTs with addr 0 silently.
>
> Meanwhile, our DT only works with UPIO_MEM but theoretically firmware
> may pass other IO types, so explicitly check against that.
>
> Tested on Loongson-LS3A4000-7A1000-NUC-SE.
>
> Fixes: 3989ed418483 ("MIPS: Loongson64: env: Fixup serial 
> clock-frequency when using LEFI")

Reviewed-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>

Sign, firmwares are always insane like this :-(

> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Yao Zi <me@xxxxxxxx>
> Signed-off-by: Rong Zhang <rongrong@xxxxxxxxxxxxxxxxx>
> ---
> Changes in v2:
> - Sort new includes alphabetically (thanks Yao Zi)
> ---
>  arch/mips/loongson64/env.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/loongson64/env.c b/arch/mips/loongson64/env.c
> index 11ddf02d6a15..7abcca7ab4ed 100644
> --- a/arch/mips/loongson64/env.c
> +++ b/arch/mips/loongson64/env.c
> @@ -17,7 +17,9 @@
>  #include <linux/dma-map-ops.h>
>  #include <linux/export.h>
>  #include <linux/libfdt.h>
> +#include <linux/minmax.h>
>  #include <linux/pci_ids.h>
> +#include <linux/serial_core.h>
>  #include <linux/string_choices.h>
>  #include <asm/bootinfo.h>
>  #include <loongson.h>
> @@ -106,9 +108,23 @@ static void __init lefi_fixup_fdt(struct 
> system_loongson *system)
> 
>  	is_loongson64g = (read_c0_prid() & PRID_IMP_MASK) == PRID_IMP_LOONGSON_64G;
> 
> -	for (i = 0; i < system->nr_uarts; i++) {
> +	for (i = 0; i < min(system->nr_uarts, MAX_UARTS); i++) {
>  		uartdev = &system->uarts[i];
> 
> +		/*
> +		 * Some firmware does not set nr_uarts properly and passes empty
> +		 * items. Ignore them silently.
> +		 */
> +		if (uartdev->uart_base == 0)
> +			continue;
> +
> +		/* Our DT only works with UPIO_MEM. */
> +		if (uartdev->iotype != UPIO_MEM) {
> +			pr_warn("Ignore UART 0x%llx with iotype %u passed by firmware\n",
> +				uartdev->uart_base, uartdev->iotype);
> +			continue;
> +		}
> +
>  		ret = lefi_fixup_fdt_serial(fdt_buf, uartdev->uart_base,
>  					    uartdev->uartclk);
>  		/*
>
> base-commit: 267594792a71018788af69e836c52e34bb8054af
> -- 
> 2.53.0

-- 
- Jiaxun