Messages in this thread | | | Date | Mon, 8 Jul 2019 21:51:11 -0700 | From | Kees Cook <> | Subject | Re: [PATCH v5 06/12] S.A.R.A.: WX protection |
| |
On Sun, Jul 07, 2019 at 05:49:35PM +0200, Salvatore Mesoraca wrote: > Al Viro <viro@zeniv.linux.org.uk> wrote: > > > > On Sat, Jul 06, 2019 at 12:54:47PM +0200, Salvatore Mesoraca wrote: > > > > > +#define sara_warn_or_return(err, msg) do { \ > > > + if ((sara_wxp_flags & SARA_WXP_VERBOSE)) \ > > > + pr_wxp(msg); \ > > > + if (!(sara_wxp_flags & SARA_WXP_COMPLAIN)) \ > > > + return -err; \ > > > +} while (0) > > > + > > > +#define sara_warn_or_goto(label, msg) do { \ > > > + if ((sara_wxp_flags & SARA_WXP_VERBOSE)) \ > > > + pr_wxp(msg); \ > > > + if (!(sara_wxp_flags & SARA_WXP_COMPLAIN)) \ > > > + goto label; \ > > > +} while (0) > > > > No. This kind of "style" has no place in the kernel. > > > > Don't hide control flow. It's nasty enough to reviewers, > > but it's pure hell on anyone who strays into your code while > > chasing a bug or doing general code audit. In effect, you > > are creating your oh-so-private C dialect and assuming that > > everyone who ever looks at your code will start with learning > > that *AND* incorporating it into their mental C parser. > > I'm sorry, but you are not that important. > > > > If it looks like a function call, a casual reader will assume > > that this is exactly what it is. And when one is scanning > > through a function (e.g. to tell if handling of some kind > > of refcounts is correct, with twentieth grep through the > > tree having brought something in your code into the view), > > the last thing one wants is to switch between the area-specific > > C dialects. Simply because looking at yours is sandwiched > > between digging through some crap in drivers/target/ and that > > weird thing in kernel/tracing/, hopefully staying limited > > to 20 seconds of glancing through several functions in your > > code. > > > > Don't Do That. Really. > > I understand your concerns. > The first version of SARA didn't use these macros, > they were added because I was asked[1] to do so. > > I have absolutely no problems in reverting this change. > I just want to make sure that there is agreement on this matter. > Maybe Kees can clarify his stance. > > Thank you for your suggestions. > > [1] https://lkml.kernel.org/r/CAGXu5jJuQx2qOt_aDqDQDcqGOZ5kmr5rQ9Zjv=MRRCJ65ERfGw@mail.gmail.com
I just didn't like how difficult it was to review the repeated checking. I thought then (and still think now) it's worth the unusual style to improve the immediate readability. Obviously Al disagrees. I'm not against dropping my suggestion; it's just a pain to review it and it seems like an area that would be highly prone to subtle typos. Perhaps some middle ground:
#define sara_warn(msg) ({ \ if ((sara_wxp_flags & SARA_WXP_VERBOSE)) \ pr_wxp(msg); \ !(sara_wxp_flags & SARA_WXP_COMPLAIN); \ })
...
if (unlikely(sara_wxp_flags & SARA_WXP_WXORX && vm_flags & VM_WRITE && vm_flags & VM_EXEC && sara_warn("W^X"))) return -EPERM;
that way the copy/pasting isn't present but the control flow is visible?
-- Kees Cook
| |