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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 02e541db05 ("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: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Cc: John Stultz <jstultz@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Masahiro Yamada 2023-09-26 17:09:03 +01:00 committed by Greg Kroah-Hartman
parent c15682ed16
commit 170ce55eff
1 changed files with 2 additions and 12 deletions
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14
arch/arm/include/asm/uaccess.h
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@ -109,16 +109,6 @@ 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") \
@ -126,7 +116,7 @@ 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__
@ -148,7 +138,7 @@ 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