arm64: errata: add module build workaround for erratum #843419

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: Luis Henriques <luis.henriques@canonical.com>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 316ed8cf5bc0bbd6cd5de1c33f8d2e481828020c..2e882e5174ab6f38def7dac5fbe9f8c55f25ad5f 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -155,6 +155,22 @@ menu "Bus support"
 config ARM_AMBA
        bool
 
+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
 
 menu "Kernel Features"

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 8185a913c5ed5ab2d659c119903666409bbb1793..be8b36304ac1ba90d5bb79ac561e3552ed6293d7 100644 (file)
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -34,6 +34,10 @@ comma = ,
 
 CHECKFLAGS     += -D__aarch64__
 
+ifeq ($(CONFIG_ARM64_ERRATUM_843419), y)
+CFLAGS_MODULE  += -mcmodel=large
+endif
+
 # Default value
 head-y         := arch/arm64/kernel/head.o
 

diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index 1eb1cc955139537e1b66cbdc78accd5830f0ca06..e366329d96d8971b064af12e3a3e7b619881f3d1 100644 (file)
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -330,12 +330,14 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
                        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;