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Message-Id: <20190131192533.34130-17-thgarnie@chromium.org>
Date: Thu, 31 Jan 2019 11:24:23 -0800
From: Thomas Garnier <thgarnie@...omium.org>
To: kernel-hardening@...ts.openwall.com
Cc: kristen@...ux.intel.com,
Thomas Garnier <thgarnie@...omium.org>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Kees Cook <keescook@...omium.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Thomas Garnier <thgarnie@...gle.com>,
Nicholas Piggin <npiggin@...il.com>,
Sam Ravnborg <sam@...nborg.org>,
Palmer Dabbelt <palmer@...ive.com>,
Michael Forney <forney@...gle.com>,
Cao jin <caoj.fnst@...fujitsu.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH v6 16/27] compiler: Option to add PROVIDE_HIDDEN replacement for weak symbols
Provide an option to have a PROVIDE_HIDDEN (linker script) entry for
each weak symbol. This option solves an error in x86_64 where the linker
optimizes PIE generated code to be non-PIE because --emit-relocs was used
instead of -pie (to reduce dynamic relocations).
Signed-off-by: Thomas Garnier <thgarnie@...omium.org>
---
init/Kconfig | 7 +++++++
scripts/link-vmlinux.sh | 14 ++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/init/Kconfig b/init/Kconfig
index 116e0de4817f..2261c9891631 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -2104,6 +2104,13 @@ config ASN1
inform it as to what tags are to be expected in a stream and what
functions to call on what tags.
+config WEAK_PROVIDE_HIDDEN
+ bool
+ help
+ Generate linker script PROVIDE_HIDDEN entries for all weak symbols. It
+ allows to prevent non-PIE code being replaced by the linker if the
+ emit-relocs option is used instead of PIE (useful for x86_64 PIE).
+
source "kernel/Kconfig.locks"
config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index bc7f1fc1f55b..abf44a804c79 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -119,6 +119,17 @@ kallsyms()
${CC} ${aflags} -c -o ${2} ${afile}
}
+gen_weak_provide_hidden()
+{
+ if [ -n "${CONFIG_WEAK_PROVIDE_HIDDEN}" ]; then
+ local pattern="s/^\s\+ w \(\w\+\)$/PROVIDE_HIDDEN(\1 = .);/gp"
+ echo -e "SECTIONS {\n. = _end;" > .tmp_vmlinux_hiddenld
+ ${NM} ${1} | sed -n "${pattern}" >> .tmp_vmlinux_hiddenld
+ echo "}" >> .tmp_vmlinux_hiddenld
+ LDFLAGS_vmlinux="${LDFLAGS_vmlinux} -T .tmp_vmlinux_hiddenld"
+ fi
+}
+
# Create map file with all symbols from ${1}
# See mksymap for additional details
mksysmap()
@@ -200,6 +211,9 @@ modpost_link vmlinux.o
# modpost vmlinux.o to check for section mismatches
${MAKE} -f "${srctree}/scripts/Makefile.modpost" vmlinux.o
+# Generate weak linker script
+gen_weak_provide_hidden vmlinux.o
+
kallsymso=""
kallsyms_vmlinux=""
if [ -n "${CONFIG_KALLSYMS}" ]; then
--
2.20.1.495.gaa96b0ce6b-goog
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