Re: [PATCH] ACPI: GTDT: Tighten the check for the first platform timer entry

[Marc Zyngier]

On Thu, 10 Oct 2024 15:47:03 +0100,
Zheng Zengkai <zhengzengkai@xxxxxxxxxx> wrote:
> 
> As suggested by Marc and Lorenzo, first we need to check whether
> the platform_timer pointer is within gtdt bounds (< gtdt_end) before
> de-referencing what it points at to detect the (first) platform
> timer entry length and check that next platform_timer pointer is
> within gtdt_end too. Now we do that only in next_platform_timer()
> for subsequent platform timers.
> 
> So add check against table length (gtdt_end) for the first platform
> timer entry.
> 
> Suggested-by: Marc Zyngier <maz@xxxxxxxxxx>
> Suggested-by: Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx>
> Signed-off-by: Zheng Zengkai <zhengzengkai@xxxxxxxxxx>
> ---
>  drivers/acpi/arm64/gtdt.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/arm64/gtdt.c b/drivers/acpi/arm64/gtdt.c
> index c0e77c1c8e09..f249af1ed1cd 100644
> --- a/drivers/acpi/arm64/gtdt.c
> +++ b/drivers/acpi/arm64/gtdt.c
> @@ -177,7 +177,8 @@ int __init acpi_gtdt_init(struct acpi_table_header *table,
>  	}
>  
>  	platform_timer = (void *)gtdt + gtdt->platform_timer_offset;
> -	if (platform_timer < (void *)table + sizeof(struct acpi_table_gtdt)) {
> +	if (platform_timer < (void *)table + sizeof(struct acpi_table_gtdt) ||
> +			platform_timer >= acpi_gtdt_desc.gtdt_end) {
>  		pr_err(FW_BUG "invalid timer data.\n");
>  		return -EINVAL;
>  	}

You  are  only  checking  the  base  pointer  for  the  platform_timer
array. This doesn't say anything about the *size* of that array (or at
least its first element), and whether that actually fits in the table.

	M.

-- 
Without deviation from the norm, progress is not possible.