Patch "arm64: errata: add module build workaround for erratum #843419" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     arm64-errata-add-module-build-workaround-for-erratum-843419.patch

and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Will Deacon <[email protected]>
Date: Tue, 17 Mar 2015 12:15:02 +0000
Subject: arm64: errata: add module build workaround for erratum #843419

From: Will Deacon <[email protected]>

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.

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

@@ -306,6 +306,22 @@ menu "CPU Power Management"
 
 source "drivers/cpuidle/Kconfig"
 
+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
 
 source "net/Kconfig"

@@ -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
 

@@ -330,12 +330,14 @@ 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;

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/arm64-head.s-initialise-mdcr_el2-in-el2_setup.patch queue-3.14/arm64-kconfig-move-list_poison-to-a-safe-value.patch queue-3.14/arm64-errata-add-module-build-workaround-for-erratum-843419.patch queue-3.14/arm64-compat-fix-vfp-save-restore-across-signal-handlers-in-big-endian.patch