Subject: Re: [PATCH v6 17/25] PCI: Fix PREL32 relocations for LTO

From: Kees Cook <[email-masked]>
Date: Wed, 14 Oct 2020 15:58:12 -0700

On Mon, Oct 12, 2020 at 05:31:55PM -0700, Sami Tolvanen wrote:
> With Clang's Link Time Optimization (LTO), the compiler can rename
> static functions to avoid global naming collisions. As PCI fixup
> functions are typically static, renaming can break references
> to them in inline assembly. This change adds a global stub to
> DECLARE_PCI_FIXUP_SECTION to fix the issue when PREL32 relocations
> are used.
> 
> Signed-off-by: Sami Tolvanen <[email-masked]>
> Acked-by: Bjorn Helgaas <[email-masked]>
> Reviewed-by: Kees Cook <[email-masked]>

Another independent patch! :) Bjorn, since you've already Acked this
patch, would be be willing to pick it up for your tree?

-Kees

> ---
>  include/linux/pci.h | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 835530605c0d..4e64421981c7 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1909,19 +1909,28 @@ enum pci_fixup_pass {
>  };
>  
>  #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
> -#define __DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class,	\
> -				    class_shift, hook)			\
> -	__ADDRESSABLE(hook)						\
> +#define ___DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class,	\
> +				    class_shift, hook, stub)		\
> +	void stub(struct pci_dev *dev);					\
> +	void stub(struct pci_dev *dev)					\
> +	{ 								\
> +		hook(dev); 						\
> +	}								\
>  	asm(".section "	#sec ", \"a\"				\n"	\
>  	    ".balign	16					\n"	\
>  	    ".short "	#vendor ", " #device "			\n"	\
>  	    ".long "	#class ", " #class_shift "		\n"	\
> -	    ".long "	#hook " - .				\n"	\
> +	    ".long "	#stub " - .				\n"	\
>  	    ".previous						\n");
> +
> +#define __DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class,	\
> +				  class_shift, hook, stub)		\
> +	___DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class,	\
> +				  class_shift, hook, stub)
>  #define DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class,	\
>  				  class_shift, hook)			\
>  	__DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class,	\
> -				  class_shift, hook)
> +				  class_shift, hook, __UNIQUE_ID(hook))
>  #else
>  /* Anonymous variables would be nice... */
>  #define DECLARE_PCI_FIXUP_SECTION(section, name, vendor, device, class,	\
> -- 
> 2.28.0.1011.ga647a8990f-goog
> 

-- 
Kees Cook

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