mingw: enable stack smashing protector

To reduce Git for Windows' attack surface, we started using the Address
Space Layout Randomization and Data Execution Prevention features in
ce6a158561f9 (mingw: enable DEP and ASLR, 2019-05-08).

To remove yet another attack vector, let's make use of gcc's stack
smashing protector that helps detect stack buffer overruns early.

Rather than using -fstack-protector, we use -fstack-protector-strong
because on Windows: The latter appears to strike a better balance
between the performance impact and the provided safety.

In a non-scientific test (time git log --grep=is -p), best of 5 timings
went from 23.009s to 22.997s, i.e. the performance impact was *well*
lost in the noise.

This fixes https://github.com/git-for-windows/git/issues/501

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/config.mak.uname b/config.mak.uname
index b71688eeb73f10da004f3d16e3de9afd13eb9c7e..2400e7879c4e2050fcc2a95091b77fbc4613928b 100644 (file)
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -596,7 +596,8 @@ else
                        BASIC_LDFLAGS += -Wl,--large-address-aware
                endif
                CC = gcc
-               COMPAT_CFLAGS += -D__USE_MINGW_ANSI_STDIO=0 -DDETECT_MSYS_TTY
+               COMPAT_CFLAGS += -D__USE_MINGW_ANSI_STDIO=0 -DDETECT_MSYS_TTY \
+                       -fstack-protector-strong
                EXTLIBS += -lntdll
                INSTALL = /bin/install
                NO_R_TO_GCC_LINKER = YesPlease