Re: [PATCH] PCI: fix out-of-bounds stack access

[Bjorn Helgaas]

On Fri, Jul 25, 2025 at 11:06:28AM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> The newly added PCI_FIND_NEXT_EXT_CAP function calls a helper that
> stores a result using a 32-bit pointer, but passes a shorter local
> variable into it. gcc-15 warns about this undefined behavior:
> 
> In function 'cdns_pcie_read_cfg',
>     inlined from 'cdns_pcie_find_capability' at drivers/pci/controller/cadence/pcie-cadence.c:31:9:
> drivers/pci/controller/cadence/pcie-cadence.c:22:22: error: write of 32-bit data outside the bound of destination object, data truncated into 8-bit [-Werror=extra]
>    22 |                 *val = cdns_pcie_readb(pcie, where);
>       |                 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In function 'dw_pcie_read_cfg',
>     inlined from 'dw_pcie_find_capability' at drivers/pci/controller/dwc/pcie-designware.c:234:9:
> drivers/pci/controller/dwc/pcie-designware.c:225:22: error: write of 32-bit data outside the bound of destination object, data truncated into 8-bit [-Werror=extra]
>   225 |                 *val = dw_pcie_readb_dbi(pci, where);
>       |                 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Change the macro to remove the invalid cast and extend the target
> variables as needed.
> 
> Fixes: 1b07388f32e1 ("PCI: Refactor extended capability search into PCI_FIND_NEXT_EXT_CAP()")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Squashed into that commit, thanks, Arnd!

  https://git.kernel.org/cgit/linux/kernel/git/pci/pci.git/commit/?id=2502a619108b

> ---
>  drivers/pci/pci.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index da5912c2017c..ac954584d991 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -109,17 +109,17 @@ int pci_bus_read_config(void *priv, unsigned int devfn, int where, u32 size,
>  ({									\
>  	int __ttl = PCI_FIND_CAP_TTL;					\
>  	u8 __id, __found_pos = 0;					\
> -	u8 __pos = (start);						\
> -	u16 __ent;							\
> +	u32 __pos = (start);						\
> +	u32 __ent;							\
>  									\
> -	read_cfg(args, __pos, 1, (u32 *)&__pos);			\
> +	read_cfg(args, __pos, 1, &__pos);				\
>  									\
>  	while (__ttl--) {						\
>  		if (__pos < PCI_STD_HEADER_SIZEOF)			\
>  			break;						\
>  									\
>  		__pos = ALIGN_DOWN(__pos, 4);				\
> -		read_cfg(args, __pos, 2, (u32 *)&__ent);		\
> +		read_cfg(args, __pos, 2, &__ent);			\
>  									\
>  		__id = FIELD_GET(PCI_CAP_ID_MASK, __ent);		\
>  		if (__id == 0xff)					\
> -- 
> 2.39.5
>