d/freebsd-skq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Support initializing stack variables on function entry

Browse Source 
There are two options:
 - WITH_INIT_ALL_ZERO: Zero all variables on the stack.
 - WITH_INIT_ALL_PATTERN: Initialize variables with well-defined patterns.

The exact pattern are a compiler implementation detail and vary by type.
They are somewhat documented in the LLVM commit message:
https://reviews.llvm.org/rL349442
I've used WITH_INIT_ALL_* to match Microsoft's InitAll feature rather
than naming them after the LLVM specific compiler flags.

In a range of consumer products, options like these are used in
both debug and production builds with debugs builds using patterns
(intended to provoke crashes on use of uninitialized values) and
production using zeros (deemed more likely to lead to harmless
misbehavior or NULL-pointer dereferences).

Reviewed by:	emaste
Obtained from:	CheriBSD
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D27131
This commit is contained in:
brooks 2020-11-10 19:15:13 +00:00
parent e85e8ebb30
commit 142137080c
7 changed files with 73 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
share/mk/bsd.compiler.mk
View File

@ -24,6 +24,7 @@
# - c++11: supports full (or nearly full) C++11 programming environment.
# - retpoline: supports the retpoline speculative execution vulnerability
# mitigation.
# - init-all: supports stack variable initialization.
#
# These variables with an X_ prefix will also be provided if XCC is set.
#
@ -214,7 +215,7 @@ ${X_}COMPILER_FEATURES= c++11 c++14
${X_}COMPILER_FEATURES+= c++17
.endif
.if ${${X_}COMPILER_TYPE} == "clang"
${X_}COMPILER_FEATURES+= retpoline
${X_}COMPILER_FEATURES+= retpoline init-all
.endif
.else

19
share/mk/bsd.lib.mk
View File

@ -85,6 +85,25 @@ LDFLAGS+= -Wl,-zretpolineplt
.endif
.endif
# Initialize stack variables on function entry
.if ${MK_INIT_ALL_ZERO} == "yes"
.if ${COMPILER_FEATURES:Minit-all}
CFLAGS+= -ftrivial-auto-var-init=zero \
-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
CXXFLAGS+= -ftrivial-auto-var-init=zero \
-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
.else
.warning InitAll (zeros) requested but not support by compiler
.endif
.elif ${MK_INIT_ALL_PATTERN} == "yes"
.if ${COMPILER_FEATURES:Minit-all}
CFLAGS+= -ftrivial-auto-var-init=pattern
CXXFLAGS+= -ftrivial-auto-var-init=pattern
.else
.warning InitAll (pattern) requested but not support by compiler
.endif
.endif
.if ${MK_DEBUG_FILES} != "no" && empty(DEBUG_FLAGS:M-g) && \
empty(DEBUG_FLAGS:M-gdwarf*)
CFLAGS+= ${DEBUG_FILES_CFLAGS}

6
share/mk/bsd.opts.mk
View File

@ -71,6 +71,8 @@ __DEFAULT_NO_OPTIONS = \
BIND_NOW \
CCACHE_BUILD \
CTF \
INIT_ALL_PATTERN \
INIT_ALL_ZERO \
INSTALL_AS_USER \
PIE \
RETPOLINE \
@ -85,6 +87,10 @@ __DEFAULT_DEPENDENT_OPTIONS = \
.include <bsd.mkopt.mk>
.if ${MK_INIT_ALL_PATTERN} == "yes" && ${MK_INIT_ALL_ZERO} == "yes"
.error WITH_INIT_ALL_PATTERN and WITH_INIT_ALL_ZERO are mutually exclusive.
.endif
#
# Supported NO_* options (if defined, MK_* will be forced to "no",
# regardless of user's setting).

19
share/mk/bsd.prog.mk
View File

@ -60,6 +60,25 @@ LDFLAGS+= -Wl,-zretpolineplt
.endif
.endif
# Initialize stack variables on function entry
.if ${MK_INIT_ALL_ZERO} == "yes"
.if ${COMPILER_FEATURES:Minit-all}
CFLAGS+= -ftrivial-auto-var-init=zero \
-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
CXXFLAGS+= -ftrivial-auto-var-init=zero \
-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
.else
.warning InitAll (zeros) requested but not support by compiler
.endif
.elif ${MK_INIT_ALL_PATTERN} == "yes"
.if ${COMPILER_FEATURES:Minit-all}
CFLAGS+= -ftrivial-auto-var-init=pattern
CXXFLAGS+= -ftrivial-auto-var-init=pattern
.else
.warning InitAll (pattern) requested but not support by compiler
.endif
.endif
.if ${MACHINE_CPUARCH} == "riscv" && ${LINKER_FEATURES:Mriscv-relaxations} == ""
CFLAGS += -mno-relax
.endif

18
sys/conf/kern.mk
View File

@ -227,6 +227,24 @@ CFLAGS+= -fstack-protector
CFLAGS+= -mretpoline
.endif
#
# Initialize stack variables on function entry
#
.if ${MK_INIT_ALL_ZERO} == "yes"
.if ${COMPILER_FEATURES:Minit-all}
CFLAGS+= -ftrivial-auto-var-init=zero \
-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
.else
.warning InitAll (zeros) requested but not support by compiler
.endif
.elif ${MK_INIT_ALL_PATTERN} == "yes"
.if ${COMPILER_FEATURES:Minit-all}
CFLAGS+= -ftrivial-auto-var-init=pattern
.else
.warning InitAll (pattern) requested but not support by compiler
.endif
.endif
#
# Add -gdwarf-2 when compiling -g. The default starting in clang v3.4
# and gcc 4.8 is to generate DWARF version 4. However, our tools don't

5
tools/build/options/WITH_INIT_ALL_PATTERN Normal file
View File

@ -0,0 +1,5 @@
.\" $FreeBSD$
Set to build the base system or kernel with stack variables initialized to
.Pq compiler defined
debugging patterns on function entry.
This option requires the clang compiler.

4
tools/build/options/WITH_INIT_ALL_ZERO Normal file
View File

@ -0,0 +1,4 @@
.\" $FreeBSD$
Set to build the base system or kernel with stack variables initialized
to zero on function entry.
This option requires that the clang compiler be used.