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




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@xxxxxxxx>
> >
> > 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
> > 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@xxxxxxxx>
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
> > ---
> >  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))))

Does that work for you?

Ciao,
Dscho