| From | Linus Torvalds <> | Date | Mon, 22 Aug 2016 15:11:32 -0700 | Subject | Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder |
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On Thu, Aug 18, 2016 at 6:06 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote: > Convert arch_within_stack_frames() to use the new unwinder.
Please don't do this.
There's no real reason to unwind the stack frame. If it's not on the current stack page, it shouldn't be a valid source anyway, so unwidning things just seems entirely pointless.
Quite frankly, I think the whole "look at the stack frames" logic should be removed from this. It's classic crap that external patches do. How many call-sites does it actually check, and how many of them aren't already checked by the existing static checks for constant addresses within existing objects?
It's entirely possible that there is simply no point what-so-ever to this all, and it mostly triggers on things like the fs/stat.c code that does
struct stat tmp; ... return copy_to_user(statbuf,&tmp,sizeof(tmp)) ? -EFAULT : 0;
where the new useraccess.c code is pure masturbatory crap.
One of the reasons I had for merging that code was that I was hoping that it would improve by being in the kernel. And by "improve" I mean "get rid of crap" rather than make it more expensive and even more self-congratulatory stupidity.
Right now, I suspect 99% of all the stack checks in usercopy.c are solidly in the "mindbogglingly stupid crap" camp.
Linus
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