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toolchain: granular choice for stack protector

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Currently, we only support two levels of stach-smashing protection:
  - entirely disabled,
  - protect _all_ functions with -fstack-protector-all.

-fstack-protector-all tends to be far too aggressive and impacts
performance too much to be worth on a real product.

Add a choice that allows us to select between different levels of
stack-smashing protection:
  - none
  - basic   (NEW)
  - strong  (NEW)
  - all

The differences are documented in the GCC online documentation:
    https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/Optimize-Options.html

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
[yann.morin.1998@free.fr:
  - rebase
  - add legacy handling
  - SSP-strong depends on gcc >= 4.9
  - slightly simple ifeq-block in package/Makefile.in
  - keep the comment in the choice; add a comment shen strong is not
    available
  - drop the defaults (only keep the legacy)
  - update commit log
]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
[Thomas:
 - only show the choice if the toolchain has SSP support
 - add details for the BR2_SSP_ALL option that it has a significant
   performance impact.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
This commit is contained in:
Steven Noonan 2015-12-27 12:07:31 +01:00 committed by Thomas Petazzoni
parent 9ac65b37bd
commit d29c7196bf
3 changed files with 56 additions and 5 deletions
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45
Config.in
View File

@ -522,12 +522,13 @@ config BR2_GOOGLE_BREAKPAD_INCLUDE_FILES
endif
config BR2_ENABLE_SSP
choice
bool "build code with Stack Smashing Protection"
default BR2_SSP_ALL if BR2_ENABLE_SSP # legacy
depends on BR2_TOOLCHAIN_HAS_SSP
help
Enable stack smashing protection support using GCCs
-fstack-protector-all option.
Enable stack smashing protection support using GCC's
-fstack-protector option family.
See http://www.linuxfromscratch.org/hints/downloads/files/ssp.txt
for details.
@ -536,7 +537,43 @@ config BR2_ENABLE_SSP
support. This is always the case for glibc and eglibc
toolchain, but is optional in uClibc toolchains.
comment "enabling Stack Smashing Protection requires support in the toolchain"
config BR2_SSP_NONE
bool "None"
help
Disable stack-smashing protection.
config BR2_SSP_REGULAR
bool "-fstack-protector"
help
Emit extra code to check for buffer overflows, such as stack
smashing attacks. This is done by adding a guard variable to
functions with vulnerable objects. This includes functions
that call alloca, and functions with buffers larger than 8
bytes. The guards are initialized when a function is entered
and then checked when the function exits. If a guard check
fails, an error message is printed and the program exits.
config BR2_SSP_STRONG
bool "-fstack-protector-strong"
depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_9
help
Like -fstack-protector but includes additional functions to be
protected - those that have local array definitions, or have
references to local frame addresses.
comment "Stack Smashing Protection strong needs a toolchain w/ gcc >= 4.9"
depends on !BR2_TOOLCHAIN_GCC_AT_LEAST_4_9
config BR2_SSP_ALL
bool "-fstack-protector-all"
help
Like -fstack-protector except that all functions are
protected. This option might have a significant performance
impact on the compiled binaries.
endchoice
comment "Stack Smashing Protection needs a toolchain w/ SSP"
depends on !BR2_TOOLCHAIN_HAS_SSP
choice

8
Config.in.legacy
View File

@ -145,6 +145,14 @@ endif
###############################################################################
comment "Legacy options removed in 2016.02"
# BR2_ENABLE_SSP is still referenced in Config.in (default in choice)
config BR2_ENABLE_SSP
bool "Stack Smashing protection now has different levels"
help
The protection offered by SSP can now be selected from different
protection levels. Be sure to review the SSP level in the build
options menu.
config BR2_PACKAGE_DIRECTFB_CLE266
bool "cle266 driver for directfb removed"
select BR2_LEGACY

8
package/Makefile.in
View File

@ -159,7 +159,13 @@ TARGET_CFLAGS += -msep-data
TARGET_CXXFLAGS += -msep-data
endif
ifeq ($(BR2_ENABLE_SSP),y)
ifeq ($(BR2_SSP_REGULAR),y)
TARGET_CFLAGS += -fstack-protector
TARGET_CXXFLAGS += -fstack-protector
else ifeq ($(BR2_SSP_STRONG),y)
TARGET_CFLAGS += -fstack-protector-strong
TARGET_CXXFLAGS += -fstack-protector-strong
else ifeq ($(BR2_SSP_ALL),y)
TARGET_CFLAGS += -fstack-protector-all
TARGET_CXXFLAGS += -fstack-protector-all
endif