Re: [PATCH 1/5] tpm: tpm_ppi: fix wrong error code returned to user space

[Jarkko Sakkinen]

On Sat, Oct 03, 2026 at 04:27:51PM +0800, Pei Xiao wrote:
> tpm_show_ppi_response() stores its return value in an acpi_status,
> a typedef of u32.  Both error paths of the function (-EINVAL on a
> malformed _DSM package, -EFAULT on a non-zero operation return
> code) end up as huge positive values when returned as ssize_t, so
> user space cannot detect the failure with the usual "ret < 0"
> check.

I have no idea what you mean by huge value and why that would be
a problem, and overall this is disconnected from the code change.

Two's complement value is correctly stored in status up until the
ssize_t cast, which results the value to be zero-extended, and
as a result corrupt the negative values.

> 
> Declare the variable as ssize_t to match the show callback's
> return type.
> 
> Fixes: 84b1667dea23 ("ACPI / TPM: replace open-coded _DSM code with helper functions")
> Assisted-by: GLM-5.3
> Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
> ---
>  drivers/char/tpm/tpm_ppi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm_ppi.c b/drivers/char/tpm/tpm_ppi.c
> index c9793a3d986d..949fb7055bea 100644
> --- a/drivers/char/tpm/tpm_ppi.c
> +++ b/drivers/char/tpm/tpm_ppi.c
> @@ -234,7 +234,7 @@ static ssize_t tpm_show_ppi_response(struct device *dev,
>  				     struct device_attribute *attr,
>  				     char *buf)
>  {
> -	acpi_status status = -EINVAL;
> +	ssize_t status = -EINVAL;
>  	union acpi_object *obj, *ret_obj;
>  	u64 req, res;
>  	struct tpm_chip *chip = to_tpm_chip(dev);
> -- 
> 2.25.1
> 

Br, Jarkko