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Commit 41a5c171 authored by Masahiro Yamada's avatar Masahiro Yamada Committed by Greg Kroah-Hartman
Browse files

ARM: 9324/1: fix get_user() broken with veneer 

commit 24d3ba0a7b44c1617c27f5045eecc4f34752ab03 upstream.

The 32-bit ARM kernel stops working if the kernel grows to the point
where veneers for __get_user_* are created.

AAPCS32 [1] states, "Register r12 (IP) may be used by a linker as a
scratch register between a routine and any subroutine it calls. It
can also be used within a routine to hold intermediate values between
subroutine calls."

However, bl instructions buried within the inline asm are unpredictable
for compilers; hence, "ip" must be added to the clobber list.

This becomes critical when veneers for __get_user_* are created because
veneers use the ip register since commit 02e541db ("ARM: 8323/1:
force linker to use PIC veneers").

[1]: https://github.com/ARM-software/abi-aa/blob/2023Q1/aapcs32/aapcs32.rst



Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Reviewed-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarRussell King (Oracle) <rmk+kernel@armlinux.org.uk>
Cc: John Stultz <jstultz@google.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d30ff330

arch/arm/include/asm/uaccess.h

+2 −12
Original line number Diff line number Diff line
@@ -145,16 +145,6 @@ extern int __get_user_64t_1(void *); 
extern int __get_user_64t_2(void *);

extern int __get_user_64t_4(void *);



#define __GUP_CLOBBER_1	"lr", "cc"

#ifdef CONFIG_CPU_USE_DOMAINS

#define __GUP_CLOBBER_2	"ip", "lr", "cc"

#else

#define __GUP_CLOBBER_2 "lr", "cc"

#endif

#define __GUP_CLOBBER_4	"lr", "cc"

#define __GUP_CLOBBER_32t_8 "lr", "cc"

#define __GUP_CLOBBER_8	"lr", "cc"



#define __get_user_x(__r2, __p, __e, __l, __s)				\

	   __asm__ __volatile__ (					\

		__asmeq("%0", "r0") __asmeq("%1", "r2")			\
@@ -162,7 +152,7 @@ extern int __get_user_64t_4(void *); 
		"bl	__get_user_" #__s				\

		: "=&r" (__e), "=r" (__r2)				\

		: "0" (__p), "r" (__l)					\

		: __GUP_CLOBBER_##__s)

		: "ip", "lr", "cc")



/* narrowing a double-word get into a single 32bit word register: */

#ifdef __ARMEB__
@@ -184,7 +174,7 @@ extern int __get_user_64t_4(void *); 
		"bl	__get_user_64t_" #__s				\

		: "=&r" (__e), "=r" (__r2)				\

		: "0" (__p), "r" (__l)					\

		: __GUP_CLOBBER_##__s)

		: "ip", "lr", "cc")

#else

#define __get_user_x_64t __get_user_x

#endif