[PATCH] ARM: current: prevent literal references from going out of range

[PATCH] ARM: current: prevent literal references from going out of range

[Ard Biesheuvel]

Nathan reports that the new get_current() accessor may cause problems at
build time due to the use of a literal to hold the address of the
variable that stores the 'current' pointer. This is due to the fact that
LLD before v14 does not support the PC-relative group relocations that
are normally used for this, and the fallback relies on literals without
emitting the literal pools explictly using the .ltorg directive.

Since emitting a literal pool in this particular case is not possible,
avoid the LOAD_SYM_ARMV6() entirely, and use the ordinary C assigment
instead.

While at it, add a .ltorg directive to the other instantiation of
LOAD_SYM_ARMV6(), which could potentially suffer from the same issue,
but can be fixed by an .ltorg directive due to the existence of an
unconditional branch right after it.

Fixes: 9c46929e7989 ("ARM: implement THREAD_INFO_IN_TASK for uniprocessor systems")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1551
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/include/asm/current.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/current.h b/arch/arm/include/asm/current.h
index 69ecf4c6c725..6b2e4c9fae35 100644
--- a/arch/arm/include/asm/current.h
+++ b/arch/arm/include/asm/current.h
@@ -39,6 +39,7 @@ static inline __attribute_const__ struct task_struct *get_current(void)
 	    "	.subsection 1					\n\t"
 	    "2: " LOAD_SYM_ARMV6(%0, __current) "		\n\t"
 	    "	b	1b					\n\t"
+	    "	.ltorg						\n\t"
 	    "	.previous					\n\t"
 	    "	.pushsection \".alt.smp.init\", \"a\"		\n\t"
 	    "	.long	0b - .					\n\t"
@@ -46,7 +47,8 @@ static inline __attribute_const__ struct task_struct *get_current(void)
 	    "	.popsection					\n\t"
 #endif
 	    : "=r"(cur));
-#elif __LINUX_ARM_ARCH__>=7 || \
+#elif __LINUX_ARM_ARCH__>= 7 || \
+      (defined(CONFIG_LD_IS_LLD) && CONFIG_LLD_VERSION < 140000) || \
       (defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS))
 	cur = __current;
 #else
-- 
2.30.2


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