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

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.

Cc: <stable@vger.kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

3 files changed, 22 insertions, 0 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 8b6e378992d2..07d1811aa03f 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -332,6 +332,22 @@ 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
 
 
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 15ff5b4156fd..f9914d7c1bb0 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -41,6 +41,10 @@ endif
 
 CHECKFLAGS      += -D__aarch64__
 
+ifeq ($(CONFIG_ARM64_ERRATUM_843419), y)
+CFLAGS_MODULE   += -mcmodel=large
+endif
+
 # Default value
 head-y          := arch/arm64/kernel/head.o
 
diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index 67bf4107f6ef..876eb8df50bf 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -332,12 +332,14 @@ 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;