5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Masahiro Yamada <masahiroy@xxxxxxxxxx>
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 02e541db0540 ("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@xxxxxxxxxx>
Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
Cc: John Stultz <jstultz@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm/include/asm/uaccess.h | 14 ++------------
1 file changed, 2 insertions(+), 12 deletions(-)
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -143,16 +143,6 @@ 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") \
@@ -160,7 +150,7 @@ 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__
@@ -182,7 +172,7 @@ 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
