[PATCH 4.1 022/159] arm64: errata: add module build workaround for erratum #843419

Greg Kroah-Hartman
2015-09-26T21:16:18Z

From: Will Deacon <will.deacon@arm.com>

commit df057cc7b4fa59e9b55f07ffdb6c62bf02e99a00 upstream.

Cortex-A53 processors <= r0p4 are affected by erratum #843419 which can
lead to a memory access using an incorrect address in certain sequences
headed by an ADRP instruction.

There is a linker fix to generate veneers for ADRP instructions, but
this doesn't work for kernel modules which are built as unlinked ELF
objects.

This patch adds a new config option for the erratum which, when enabled,
builds kernel modules with the mcmodel=large flag. This uses absolute
addressing for all kernel symbols, thereby removing the use of ADRP as
a PC-relative form of addressing. The ADRP relocs are removed from the
module loader so that we fail to load any potentially affected modules.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/Kconfig | 16 ++++++++++++++++
arch/arm64/Makefile | 4 ++++
arch/arm64/kernel/module.c | 2 ++
3 files changed, 22 insertions(+)

--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -413,6 +413,22 @@ config ARM64_ERRATUM_845719

If unsure, say Y.

+config ARM64_ERRATUM_843419
+ bool "Cortex-A53: 843419: A load or store might access an incorrect address"
+ depends on MODULES
+ default y
+ help
+ This option builds kernel modules using the large memory model in
+ order to avoid the use of the ADRP instruction, which can cause
+ a subsequent memory access to use an incorrect address on Cortex-A53
+ parts up to r0p4.
+
+ Note that the kernel itself must be linked with a version of ld
+ which fixes potentially affected ADRP instructions through the
+ use of veneers.
+
+ If unsure, say Y.
+
endmenu

--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -30,6 +30,10 @@ endif

CHECKFLAGS += -D__aarch64__

+ifeq ($(CONFIG_ARM64_ERRATUM_843419), y)
+CFLAGS_MODULE += -mcmodel=large
+endif
+
# Default value
head-y := arch/arm64/kernel/head.o

--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -332,12 +332,14 @@ int apply_relocate_add(Elf64_Shdr *sechd
ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 0, 21,
AARCH64_INSN_IMM_ADR);
break;
+#ifndef CONFIG_ARM64_ERRATUM_843419
case R_AARCH64_ADR_PREL_PG_HI21_NC:
overflow_check = false;
case R_AARCH64_ADR_PREL_PG_HI21:
ovf = reloc_insn_imm(RELOC_OP_PAGE, loc, val, 12, 21,
AARCH64_INSN_IMM_ADR);
break;
+#endif
case R_AARCH64_ADD_ABS_LO12_NC:
case R_AARCH64_LDST8_ABS_LO12_NC:
overflow_check = false;