From fd045f6cd98ec4953147b318418bd45e441e52a3 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 24 Nov 2015 12:37:35 +0100 Subject: arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel Signed-off-by: Catalin Marinas --- arch/arm64/Kconfig | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'arch/arm64/Kconfig') diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index cfa1cc90ebf4..c85c29d660bd 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -395,6 +395,7 @@ config ARM64_ERRATUM_843419 bool "Cortex-A53: 843419: A load or store might access an incorrect address" depends on MODULES default y + select ARM64_MODULE_CMODEL_LARGE help This option builds kernel modules using the large memory model in order to avoid the use of the ADRP instruction, which can cause @@ -778,6 +779,14 @@ config ARM64_UAO regular load/store instructions if the cpu does not implement the feature. +config ARM64_MODULE_CMODEL_LARGE + bool + +config ARM64_MODULE_PLTS + bool + select ARM64_MODULE_CMODEL_LARGE + select HAVE_MOD_ARCH_SPECIFIC + endmenu menu "Boot options" -- cgit v1.2.3