linux-kernel - [PATCH 1/5] arch: enable relative relocations for arm64, power, x86, s390 and x86

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Date:   Mon, 14 Aug 2017 11:52:27 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Will Deacon <will.deacon@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Garnier <thgarnie@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Petr Mladek <pmladek@...e.com>, Ingo Molnar <mingo@...hat.com>,
        James Morris <james.l.morris@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Pitre <nico@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jessica Yu <jeyu@...nel.org>, x86@...nel.org
Subject: [PATCH 1/5] arch: enable relative relocations for arm64, power, x86, s390 and x86

Before updating certain subsystems to use place relative 32-bit
relocations in special sections, to save space  and reduce the
number of absolute relocations that need to be processed at runtime
by relocatable kernels, introduce a new Kconfig symbol and define it
for some architectures that should be able to support and benefit
from it.

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 arch/Kconfig                    | 10 ++++++++++
 arch/arm64/Kconfig              |  1 +
 arch/arm64/kernel/vmlinux.lds.S |  2 +-
 arch/powerpc/Kconfig            |  1 +
 arch/s390/Kconfig               |  1 +
 arch/x86/Kconfig                |  1 +
 6 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 21d0089117fe..4e77d8e8697e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -940,4 +940,14 @@ config REFCOUNT_FULL
 	  against various use-after-free conditions that can be used in
 	  security flaw exploits.
 
+config HAVE_ARCH_PREL32_RELOCATIONS
+	bool
+	help
+	  May be selected by an architecture if it supports place-relative
+	  32-bit relocations, both in the toolchain and in the module loader,
+	  in which case relative references can be used in special sections
+	  for PCI fixup, initcalls etc which are only half the size on 64 bit
+	  architectures, and don't require runtime relocation on relocatable
+	  kernels.
+
 source "kernel/gcov/Kconfig"
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index dfd908630631..ce05d2d8143e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -72,6 +72,7 @@ config ARM64
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
+	select HAVE_ARCH_PREL32_RELOCATIONS
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 987a00ee446c..5849bd4e2b06 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -171,7 +171,7 @@ SECTIONS
 		CON_INITCALL
 		SECURITY_INITCALL
 		INIT_RAM_FS
-		*(.init.rodata.* .init.bss)	/* from the EFI stub */
+		*(.init.rodata.* .init.bss .init.discard.*)	/* from the EFI stub */
 	}
 	.exit.data : {
 		ARM_EXIT_KEEP(EXIT_DATA)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 36f858c37ca7..f7e60ed5bdd0 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -163,6 +163,7 @@ config PPC
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
+	select HAVE_ARCH_PREL32_RELOCATIONS
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select ARCH_HAS_STRICT_KERNEL_RWX	if (PPC_BOOK3S_64 && !RELOCATABLE && !HIBERNATION)
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 7eeb75d758c1..1206cc7daa0d 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -127,6 +127,7 @@ config S390
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_JUMP_LABEL
 	select CPU_NO_EFFICIENT_FFS if !HAVE_MARCH_Z9_109_FEATURES
+	select HAVE_ARCH_PREL32_RELOCATIONS
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_SOFT_DIRTY
 	select HAVE_ARCH_TRACEHOOK
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 781521b7cf9e..77246125883e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -112,6 +112,7 @@ config X86
 	select HAVE_ARCH_MMAP_RND_BITS		if MMU
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if MMU && COMPAT
 	select HAVE_ARCH_COMPAT_MMAP_BASES	if MMU && COMPAT
+	select HAVE_ARCH_PREL32_RELOCATIONS
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
-- 
2.11.0