arm64: assembler: make adr_l work in modules under KASLR

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>

1 files changed, 27 insertions, 9 deletions

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 446f6c46d4b1..3a4301163e04 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -164,22 +164,25 @@ 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
 
         /*
@@ -190,6 +193,7 @@ 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]
@@ -197,6 +201,15 @@ 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
 
         /*
@@ -206,8 +219,13 @@ 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
 
         /*