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Commit df057cc7 authored by Will Deacon's avatar Will Deacon
Browse files

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: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent bdec97a8

arch/arm64/Kconfig

+16 −0
Original line number Diff line number Diff line
@@ -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

arch/arm64/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -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

arch/arm64/kernel/module.c

+2 −0
Original line number Diff line number Diff line
@@ -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;