[PATCH 4.4 072/101] arm64: assembler: make adr_l work in modules under KASLR

Greg Kroah-Hartman
2017-07-03T13:39:26Z

From: Ard Biesheuvel <ard.biesheuvel@linaro.org>

[ Upstream commit 41c066f2c4d436c535616fe182331766c57838f0 ]

When CONFIG_RANDOMIZE_MODULE_REGION_FULL=y, the offset between loaded
modules and the core kernel may exceed 4 GB, putting symbols exported
by the core kernel out of the reach of the ordinary adrp/add instruction
pairs used to generate relative symbol references. So make the adr_l
macro emit a movz/movk sequence instead when executing in module context.

While at it, remove the pointless special case for the stack pointer.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/include/asm/assembler.h | 36 +++++++++++++++++++++++++++---------
1 file changed, 27 insertions(+), 9 deletions(-)

--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -147,22 +147,25 @@ lr .req x30 // link register

/*
* Pseudo-ops for PC-relative adr/ldr/str <reg>, <symbol> where
- * <symbol> is within the range +/- 4 GB of the PC.
+ * <symbol> is within the range +/- 4 GB of the PC when running
+ * in core kernel context. In module context, a movz/movk sequence
+ * is used, since modules may be loaded far away from the kernel
+ * when KASLR is in effect.
*/
/*
* @dst: destination register (64 bit wide)
* @sym: name of the symbol
- * @tmp: optional scratch register to be used if <dst> == sp, which
- * is not allowed in an adrp instruction
*/
- .macro adr_l, dst, sym, tmp=
- .ifb \tmp
+ .macro adr_l, dst, sym
+#ifndef MODULE
adrp \dst, \sym
add \dst, \dst, :lo12:\sym
- .else
- adrp \tmp, \sym
- add \dst, \tmp, :lo12:\sym
- .endif
+#else
+ movz \dst, #:abs_g3:\sym
+ movk \dst, #:abs_g2_nc:\sym
+ movk \dst, #:abs_g1_nc:\sym
+ movk \dst, #:abs_g0_nc:\sym
+#endif
.endm

/*
@@ -173,6 +176,7 @@ lr .req x30 // link register
* the address
*/
.macro ldr_l, dst, sym, tmp=
+#ifndef MODULE
.ifb \tmp
adrp \dst, \sym
ldr \dst, [\dst, :lo12:\sym]
@@ -180,6 +184,15 @@ lr .req x30 // link register
adrp \tmp, \sym
ldr \dst, [\tmp, :lo12:\sym]
.endif
+#else
+ .ifb \tmp
+ adr_l \dst, \sym
+ ldr \dst, [\dst]
+ .else
+ adr_l \tmp, \sym
+ ldr \dst, [\tmp]
+ .endif
+#endif
.endm

/*
@@ -189,8 +202,13 @@ lr .req x30 // link register
* while <src> needs to be preserved.
*/
.macro str_l, src, sym, tmp
+#ifndef MODULE
adrp \tmp, \sym
str \src, [\tmp, :lo12:\sym]
+#else
+ adr_l \tmp, \sym
+ str \src, [\tmp]
+#endif
.endm

/*