Re: [PATCH 2/2] mingw: enable DEP and ASLR

[Alban Gruin <alban.gruin@gmail.com>]

Hi Johannes,

Le 01/05/2019 à 00:41, Johannes Schindelin a écrit :
> Hi Hannes,
> 
> On Tue, 30 Apr 2019, Johannes Sixt wrote:
> 
>> [had to add Dscho as recipient manually, mind you]
> 
> I usually pick up responses to GitGitGadget patch series even if I am not
> on explicit Cc: (but it might take a couple of days when I am too busy
> elsewhere to read the Git mailing list).
> 
>> Am 29.04.19 um 23:56 schrieb İsmail Dönmez via GitGitGadget:
>>> From: =?UTF-8?q?=C4=B0smail=20D=C3=B6nmez?= <ismail@i10z.com>
>>>
>>> Enable DEP (Data Execution Prevention) and ASLR (Address Space Layout
>>> Randomization) support. This applies to both 32bit and 64bit builds
>>> and makes it substantially harder to exploit security holes in Git by
>>> offering a much more unpredictable attack surface.
>>>
>>> ASLR interferes with GDB's ability to set breakpoints. A similar issue
>>> holds true when compiling with -O2 (in which case single-stepping is
>>> messed up because GDB cannot map the code back to the original source
>>> code properly). Therefore we simply enable ASLR only when an

I don’t know if it stands true when combined with something like -ggdb3,
but I may be very wrong.  Feel free to correct me.

>>> optimization flag is present in the CFLAGS, using it as an indicator
>>> that the developer does not want to debug in GDB anyway.
>>>
>>> Signed-off-by: İsmail Dönmez <ismail@i10z.com>
>>> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
>>> ---
>>>  config.mak.uname | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/config.mak.uname b/config.mak.uname
>>> index e7c7d14e5f..a9edcc5f0b 100644
>>> --- a/config.mak.uname
>>> +++ b/config.mak.uname
>>> @@ -570,6 +570,12 @@ else
>>>  	ifeq ($(shell expr "$(uname_R)" : '2\.'),2)
>>>  		# MSys2
>>>  		prefix = /usr/
>>> +		# Enable DEP
>>> +		BASIC_LDFLAGS += -Wl,--nxcompat
>>> +		# Enable ASLR (unless debugging)
>>> +		ifneq (,$(findstring -O,$(CFLAGS)))
>>> +			BASIC_LDFLAGS += -Wl,--dynamicbase
>>> +		endif
>>>  		ifeq (MINGW32,$(MSYSTEM))
>>>  			prefix = /mingw32
>>>  			HOST_CPU = i686
>>>
>>
>> I'm a bit concerned that this breaks my debug sessions where I use -O0.
>> But I'll test without -O0 before I really complain.
> 
> Weird. Jameson Miller also mentioned this very concern in an internal
> review.
> 
> I guess I'll do something like
> 
> 	ifneq (,$(findstring -O,$(filter-out -O0,$(CFLAGS))))
> 

-Og also exists to debug[0], even if it’s far less known.  Perhaps it’s
better to check for -g (and its variants[1]) as the user clearly states
their intent to debug the resulting binary, rather than checking for
special cases.

> Does that work for you?
> 
> Ciao,
> Dscho
> 

[0] https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-Og
[1] https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html

Cheers,
Alban