linux-kernel - [PATCH 13/15] arm64: add a workaround for GNU gold with ARM64_MODULE

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Message-Id: <20171103171203.107569-17-samitolvanen@google.com>
Date:   Fri,  3 Nov 2017 10:12:00 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 13/15] arm64: add a workaround for GNU gold with ARM64_MODULE_PLTS

CONFIG_CLANG_LTO depends on GNU gold and due to a known bug, the
linker crashes when ARM64_MODULE_PLTS is enabled:

  https://sourceware.org/bugzilla/show_bug.cgi?id=14592

To work around the problem, this change:

  1) Enables ARM64_MODULE_PLTS only when it's needed, i.e. when
     RANDOMIZE_MODULE_REGION_FULL is selected,

  2) and disables RANDOMIZE_MODULE_REGION_FULL with clang LTO.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 arch/arm64/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 43ccddb7c8ec..a301fdc90319 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -997,8 +997,8 @@ config RELOCATABLE
 
 config RANDOMIZE_BASE
 	bool "Randomize the address of the kernel image"
-	select ARM64_MODULE_PLTS if MODULES
 	select RELOCATABLE
+	select ARM64_MODULE_PLTS if RANDOMIZE_MODULE_REGION_FULL
 	help
 	  Randomizes the virtual address at which the kernel image is
 	  loaded, as a security feature that deters exploit attempts
@@ -1016,7 +1016,7 @@ config RANDOMIZE_BASE
 
 config RANDOMIZE_MODULE_REGION_FULL
 	bool "Randomize the module region independently from the core kernel"
-	depends on RANDOMIZE_BASE
+	depends on RANDOMIZE_BASE && !CLANG_LTO
 	default y
 	help
 	  Randomizes the location of the module region without considering the
-- 
2.15.0.403.gc27cc4dac6-goog