mingw: enable GCC's stack smashing protector

Recently, I managed to upstream the Data Execution Prevention/Address Space Layout Randomization patches of Git for Windows. Now it is time to add to that by also enabling GCC's augmenting feature which reduces the attack surface even further.

Johannes Schindelin (1):
mingw: enable stack smashing protector

 config.mak.uname | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

base-commit: aa25c82427ae70aebf3b8f970f2afd54e9a2a8c6
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-215%2Fdscho%2Fmingw-stack-smashing-protector-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-215/dscho/mingw-stack-smashing-protector-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/215

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From: Johannes Schindelin <[email protected]>

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

---
 config.mak.uname | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index b71688eeb7..2400e7879c 100644
@@ -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

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