Re: [PATCH 13/19] usb: typec: anx7411: zero on-stack alt mode descriptors

[Benson Leung <bleung@google.com>]

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On Tue, Oct 27, 2026 at 03:57:53PM +0100, Greg Kroah-Hartman wrote:
> From: Josef Bacik <josef@toxicpanda.com>
> 
> typec_port_register_altmodes() and anx7411_typec_register_altmode() fill a
> struct typec_altmode_desc on the stack member by member: svid, vdo, mode.
> typec_register_altmode() reads three more members:
> 
>  - inactive: a port alternate mode is registered with active = !inactive.
>    If the byte of stack garbage is not 0, the mode starts disabled and
>    typec_altmode_enter() refuses it with -EPERM until somebody writes to
>    the "active" attribute of the port;
>  - mode_selection: the DisplayPort and Thunderbolt drivers enter the mode
>    on their own only if it is false. For the partner alternate modes of
>    anx7411, garbage there means that the mode is never entered;
>  - roles: decides what supported_roles of the port alternate mode shows.
> 
> typec_port_register_altmodes() is what tcpm and anx7411 register the
> alternate modes of their ports with.
> CONFIG_INIT_STACK_ALL_ZERO=y hides the problem.
> 
> Fixes: 183b194d8fb6 ("usb: typec: Make active on port altmode writable")
> Fixes: be727d400066 ("usb: typec: Introduce mode_selection bit")
> Fixes: 7b458a4c5d73 ("usb: typec: Add typec_port_register_altmodes()")
> Cc: stable <stable@kernel.org>
> Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> Cc: Benson Leung <bleung@chromium.org>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Reviewed-by: Benson Leung <bleung@chromium.org>

Adding abhishekpandit@google.com and abhishekpandit@google.com as a FYI.
I think we've run into this class of failure before when we were developing
mode selection.


> ---
>  drivers/usb/typec/anx7411.c | 2 +-
>  drivers/usb/typec/class.c   | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/typec/anx7411.c b/drivers/usb/typec/anx7411.c
> index 06c25af094b3..ac122ab3175a 100644
> --- a/drivers/usb/typec/anx7411.c
> +++ b/drivers/usb/typec/anx7411.c
> @@ -552,7 +552,7 @@ static int anx7411_typec_register_altmode(struct anx7411_data *ctx,
>  					  int svid, int vdo)
>  {
>  	struct device *dev = &ctx->spi_client->dev;
> -	struct typec_altmode_desc desc;
> +	struct typec_altmode_desc desc = {};
>  	int err;
>  	int i;
>  
> diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
> index 54c7810b563b..9d9703c70820 100644
> --- a/drivers/usb/typec/class.c
> +++ b/drivers/usb/typec/class.c
> @@ -2684,7 +2684,7 @@ void typec_port_register_altmodes(struct typec_port *port,
>  	struct typec_altmode **altmodes, size_t n)
>  {
>  	struct fwnode_handle *child;
> -	struct typec_altmode_desc desc;
> +	struct typec_altmode_desc desc = {};
>  	struct typec_altmode *alt;
>  	size_t index = 0;
>  	u16 svid;
> 
> -- 
> 2.56.0
> 

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