[Buildroot] [PATCH v7 1/4] toolchain/toolchain-wrapper: add BR2_RELRO_
Matt Weber
matthew.weber at rockwellcollins.com
Mon Sep 17 21:21:49 UTC 2018
The RELRO/PIE flags are currently passed via CFLAGS/LDFLAGS and this patch
proposes moving them to the toolchain wrapper.
(1) The flags should _always_ be passed, without leaving the possibility
for any package to ignore them. I.e, when BR2_RELRO_FULL=y is used
in a build, all executables should be built PIE. Passing those
options through the wrapper ensures they are used during the build
of all packages.
(2) Some options are incompatible with -fPIE. For example, when
building object files for a shared libraries, -fPIC is used, and
-fPIE shouldn't be used in combination with -fPIE. Similarly, -r
or -static are directly incompatible as they are different link
time behaviors then the intent of PIE. Passing those options
through the wrapper allows to add some "smart" logic to only pass
-fPIE/-pie when relevant.
(3) Some toolchain, kernel and bootloader packages may want to
explicitly disable PIE in a build where the rest of the userspace
has intentionally enabled it. The wrapper provides an option
to key on the -fno-pie/-no-pie and bypass the appending of RELRO
flags.
The current Kernel and U-boot source trees include this option.
https://github.com/torvalds/linux/commit/8438ee76b004ef66d125ade64c91fc128047d244
https://github.com/u-boot/u-boot/commit/6ace36e19a8cfdd16ce7c02625edf36864897bf5
If using PIE with a older Kernel and/or U-boot version, a backport of these
changes might be required. However this patchset also uses the
__KERNEL__ and __UBOOT__ defines as a way to disable PIE.
NOTE: The current implementation via CFLAGS/LDFLAGS is has caused some
build time failures as the conditional logic doesn't yet exist in
Buildroot.
https://bugs.busybox.net/show_bug.cgi?id=11206
https://bugs.busybox.net/show_bug.cgi?id=11321
Good summary of the most common build failures related to
enabling pie. https://wiki.ubuntu.com/SecurityTeam/PIE
Signed-off-by: Matthew Weber <matthew.weber at rockwellcollins.com>
---
Changes
v6 -> v7
- Fixed rebase error with a stray endif
v5 -> v6
[Thomas
- Fixed commit logs description to describe the change
- Moved relro partial options to wrapper and updated this commit
title to make the patch generically capture the move of _RELRO_
- Added comment to wrapper and commit about use of no-pie
- Added a comment in the wrapper and above to cover conversation on
Linux kernel and uboot no-pie fix-ups. Plus added a condition
checking for the __KERNEL__ and __UBOOT__ defines
- Add comment that -fPIE and -pie can interchangeably be used during
link/compile and are correctly ignored when not used.
[Arnout
- Collapsed the -pie conditional in the wrapper to be within the
check for use of -fPIE. Also resolves missing -Wl,-r in the -fPIE loop
- Removed specfile and consolidated into just the gcc frontend wrapper
v4 -> v5
- Found -r can also be -wl,r. Wrapper has been updated to cover
that case.
v3 -> v4
[Matt W
- Added no-pie/pic options to allow per package tweaking of
wrapper setting the option. This lines up with other distros
[Arnout
- After realizing that a LD invocation doesn't use the specfile,
I agree with Arnout and have tested the solution can completely
occur within the compiler wrapper. This version updates to just
have modifications in the wrapper.
v2 -> v3
- Fell back on a linker approach using a spec file and kept compiler
flag tweaks in the wrapper
v1 -> v2
- Reworked handling of pie/pic/shared to replace each time they
occur with a dummy string and then insert the right combination
when rebuilding the exec string.
- Fixed mix of tabs and spaces
- Swapped order of shared and pie. Originally coded it backwards.
---
package/Makefile.in | 11 ------
toolchain/toolchain-wrapper.c | 82 ++++++++++++++++++++++++++++++++++++++++--
toolchain/toolchain-wrapper.mk | 6 ++++
3 files changed, 86 insertions(+), 13 deletions(-)
diff --git a/package/Makefile.in b/package/Makefile.in
index abfdb81..cd21482 100644
--- a/package/Makefile.in
+++ b/package/Makefile.in
@@ -141,9 +141,6 @@ ifeq ($(BR2_DEBUG_3),y)
TARGET_DEBUGGING = -g3
endif
-TARGET_CFLAGS_RELRO = -Wl,-z,relro
-TARGET_CFLAGS_RELRO_FULL = -Wl,-z,now $(TARGET_CFLAGS_RELRO)
-
TARGET_LDFLAGS = $(call qstrip,$(BR2_TARGET_LDFLAGS))
ifeq ($(BR2_SSP_REGULAR),y)
@@ -154,14 +151,6 @@ else ifeq ($(BR2_SSP_ALL),y)
TARGET_HARDENED += -fstack-protector-all
endif
-ifeq ($(BR2_RELRO_PARTIAL),y)
-TARGET_HARDENED += $(TARGET_CFLAGS_RELRO)
-TARGET_LDFLAGS += $(TARGET_CFLAGS_RELRO)
-else ifeq ($(BR2_RELRO_FULL),y)
-TARGET_HARDENED += -fPIE $(TARGET_CFLAGS_RELRO_FULL)
-TARGET_LDFLAGS += -pie $(TARGET_CFLAGS_RELRO_FULL)
-endif
-
ifeq ($(BR2_FORTIFY_SOURCE_1),y)
TARGET_HARDENED += -D_FORTIFY_SOURCE=1
else ifeq ($(BR2_FORTIFY_SOURCE_2),y)
diff --git a/toolchain/toolchain-wrapper.c b/toolchain/toolchain-wrapper.c
index c5eb813..153ba87 100644
--- a/toolchain/toolchain-wrapper.c
+++ b/toolchain/toolchain-wrapper.c
@@ -49,8 +49,12 @@ static char _date_[sizeof("-D__DATE__=\"MMM DD YYYY\"")];
* -D__TIME__=
* -D__DATE__=
* -Wno-builtin-macro-redefined
+ * -Wl,-z,now
+ * -Wl,-z,relro
+ * -fPIE
+ * -pie
*/
-#define EXCLUSIVE_ARGS 6
+#define EXCLUSIVE_ARGS 10
static char *predef_args[] = {
#ifdef BR_CCACHE
@@ -236,7 +240,8 @@ int main(int argc, char **argv)
char *env_debug;
char *paranoid_wrapper;
int paranoid;
- int ret, i, count = 0, debug;
+ int ret, i, j, count = 0, debug;
+ unsigned int found_shared = 0;
/* Calculate the relative paths */
basename = strrchr(progpath, '/');
@@ -363,6 +368,79 @@ int main(int argc, char **argv)
*cur++ = "-Wno-builtin-macro-redefined";
}
+#ifdef BR2_RELRO_FULL
+ /* Patterned after Fedora/Gentoo hardening approaches.
+ * https://fedoraproject.org/wiki/Changes/Harden_All_Packages
+ * https://wiki.gentoo.org/wiki/Hardened/Toolchain#Position_Independent_Executables_.28PIEs.29
+ *
+ * A few checks are added to enable disabling of PIE
+ * 1) -fno-pie and -no-pie are used by other distros to disable PIE in
+ * cases where the compiler enables it by default. The logic below
+ * maintains that behavior.
+ * Ref: https://wiki.ubuntu.com/SecurityTeam/PIE
+ * 2) A check for -fno-PIE has been used in older Linux Kernel builds
+ * in a similar way to -fno-pie or -no-pie.
+ * 3) A check is added for Kernel and U-boot defines
+ * (-D__KERNEL__ and -D__UBOOT__).
+ */
+ for (i = 1; i < argc; i++) {
+ /* Apply all incompatible link flag and disable checks first */
+ if (!strcmp(argv[i], "-r") ||
+ !strcmp(argv[i], "-Wl,-r") ||
+ !strcmp(argv[i], "-static") ||
+ !strcmp(argv[i], "-D__KERNEL__") ||
+ !strcmp(argv[i], "-D__UBOOT__") ||
+ !strcmp(argv[i], "-fno-pie") ||
+ !strcmp(argv[i], "-fno-PIE") ||
+ !strcmp(argv[i], "-no-pie"))
+ break;
+ /* Record that shared was present which disables -pie but don't
+ * break out of loop as a check needs to occur that possibly
+ * still allows -fPIE to be set
+ */
+ if (!strcmp(argv[i], "-shared"))
+ found_shared = 1;
+ }
+ if (i == argc) {
+ /* Compile and link condition checking have been kept split
+ * between these two loops, as there maybe already valid
+ * compile flags set for position independence. In that case
+ * the wrapper just adds the -pie for link.
+ */
+ for (j = 1; j < argc; j++) {
+ if (!strcmp(argv[j], "-fpie") ||
+ !strcmp(argv[j], "-fPIE") ||
+ !strcmp(argv[j], "-fpic") ||
+ !strcmp(argv[j], "-fPIC"))
+ break;
+ }
+ /* Both args below can be set at compile/link time
+ * and are ignored correctly when not used
+ */
+ if(j == argc)
+ *cur++ = "-fPIE";
+
+ if (!found_shared)
+ *cur++ = "-pie";
+ }
+#endif
+ /* Are we building the Linux Kernel or U-Boot? */
+ for (i = 1; i < argc; i++) {
+ if (!strcmp(argv[i], "-D__KERNEL__") ||
+ !strcmp(argv[i], "-D__UBOOT__"))
+ break;
+ }
+ if (i == argc) {
+ /* https://wiki.gentoo.org/wiki/Hardened/Toolchain#Mark_Read-Only_Appropriate_Sections */
+#ifdef BR2_RELRO_PARTIAL
+ *cur++ = "-Wl,-z,relro";
+#endif
+#ifdef BR2_RELRO_FULL
+ *cur++ = "-Wl,-z,now";
+ *cur++ = "-Wl,-z,relro";
+#endif
+ }
+
paranoid_wrapper = getenv("BR_COMPILER_PARANOID_UNSAFE_PATH");
if (paranoid_wrapper && strlen(paranoid_wrapper) > 0)
paranoid = 1;
diff --git a/toolchain/toolchain-wrapper.mk b/toolchain/toolchain-wrapper.mk
index b8074ef..99d3039 100644
--- a/toolchain/toolchain-wrapper.mk
+++ b/toolchain/toolchain-wrapper.mk
@@ -45,6 +45,12 @@ ifeq ($(BR2_CCACHE_USE_BASEDIR),y)
TOOLCHAIN_WRAPPER_ARGS += -DBR_CCACHE_BASEDIR='"$(BASE_DIR)"'
endif
+ifeq ($(BR2_RELRO_PARTIAL),y)
+TOOLCHAIN_WRAPPER_ARGS += -DBR2_RELRO_PARTIAL
+else ifeq ($(BR2_RELRO_FULL),y)
+TOOLCHAIN_WRAPPER_ARGS += -DBR2_RELRO_FULL
+endif
+
define TOOLCHAIN_WRAPPER_BUILD
$(HOSTCC) $(HOST_CFLAGS) $(TOOLCHAIN_WRAPPER_ARGS) \
-s -Wl,--hash-style=$(TOOLCHAIN_WRAPPER_HASH_STYLE) \
--
1.9.1
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