Subject: Re: [PATCH] powerpc: drop port I/O helpers for CONFIG_HAS_IOPORT=n

From: Michael Ellerman <[email-masked]>
Date: Thu, 18 Apr 2024 16:26:40 +1000

Arnd Bergmann <[email-masked]> writes:
> From: Arnd Bergmann <[email-masked]>
>
> Calling inb()/outb() on powerpc when CONFIG_PCI is disabled causes
> a NULL pointer dereference, which is bad for a number of reasons.
>
> After my patch to turn on -Werror in linux-next, this caused a
> compiler-time warning with clang:
>
> In file included from arch/powerpc/include/asm/io.h:672:
> arch/powerpc/include/asm/io-defs.h:43:1: error: performing pointer
> arithmetic on a null pointer has undefined behavior
> [-Werror,-Wnull-pointer-arithmetic]
>    43 | DEF_PCI_AC_NORET(insb, (unsigned long p, void *b, unsigned long c),
>       | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    44 |                  (p, b, c), pio, p)
>       |                  ~~~~~~~~~~~~~~~~~~
>
> In this configuration, CONFIG_HAS_IOPORT is already disabled, and all
> drivers that use inb()/outb() should now depend on that (some patches are
> still in the process of getting marged).
>
> Hide all references to inb()/outb() in the powerpc code and the definitions
> when HAS_IOPORT is disabled to remove the possible NULL pointer access.
> The same should happin in asm-generic in the near future, but for now
> the empty inb() macros are still defined to ensure the generic version
> does not get pulled in.
>
> Signed-off-by: Arnd Bergmann <[email-masked]>
> Reported-by: Naresh Kamboju <[email-masked]>
> --

This needs a small fixup:

diff --git a/arch/powerpc/include/asm/io.h b/arch/powerpc/include/asm/io.h
index 86c212fcbc0c..60c80d0baf40 100644
--- a/arch/powerpc/include/asm/io.h
+++ b/arch/powerpc/include/asm/io.h
@@ -692,6 +692,7 @@ static inline void name at                                  \
 #define writesw writesw
 #define writesl writesl

+#ifdef CONFIG_HAS_IOPORT
 #define inb inb
 #define inw inw
 #define inl inl
@@ -704,6 +705,8 @@ static inline void name at                                  \
 #define outsb outsb
 #define outsw outsw
 #define outsl outsl
+#endif // CONFIG_HAS_IOPORT
+
 #ifdef __powerpc64__
 #define readq  readq
 #define writeq writeq

I'm running it through some randconfig builds now.

cheers