On Mon, Oct 09, 2023 at 12:15:17PM +0200, Thomas Huth wrote: > On 09/10/2023 09.44, Thomas Huth wrote: > > On 05/10/2023 19.38, Daniel P. Berrangé wrote: > > > When variables are used without being initialized, there is potential > > > to take advantage of data that was pre-existing on the stack from an > > > earlier call, to drive an exploit. > > > > > > It is good practice to always initialize variables, and the compiler > > > can warn about flaws when -Wuninitialized is present. This warning, > > > however, is by no means foolproof with its output varying depending > > > on compiler version and which optimizations are enabled. > > > > > > The -ftrivial-auto-var-init option can be used to tell the compiler > > > to always initialize all variables. This increases the security and > > > predictability of the program, closing off certain attack vectors, > > > reducing the risk of unsafe memory disclosure. > > > > > > While the option takes several possible values, using 'zero' is > > > considered to be the option that is likely to lead to semantically > > > correct or safe behaviour[1]. eg sizes/indexes are not likely to > > > lead to out-of-bounds accesses when initialized to zero. Pointers > > > are less likely to point something useful if initialized to zero. > > > > > > Even with -ftrivial-auto-var-init=zero set, GCC will still issue > ... > > > + '-ftrivial-var-auto-init=zero', > > > ] > > There is something fishy here: In the commit description, you write about > "-ftrivial-auto-var-init" but in the code you use "-ftrivial-var-auto-init" > ... that looks wrong to me, please fix!
Face palm, -ftrivial-auto-var-init is the correct one. > > I was a little bit torn about using =zero when I first read your patch, > > but after looking at [1], I tend now also tend to agree that =zero is > > likely the best choice. > > Thinking about this twice: What about using -ftrivial-var-auto-init=pattern > for --enable-debug builds, and only use the "zero" init for non-debug > builds? ... that would prevent that people blindly rely on this "language > extension". We can't blindly rely on it, because -Wuninitialized is still going to do static analysis and warn in most cases, which can't be ignored when -Werror is set. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
