linux-kernel - Re: [PATCH 0/1] uprobes: Kill __replace_page(), change uprobe_write

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 10 Dec 2013 21:04:26 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	Borislav Petkov <bp@...en8.de>,
	Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>, Jiri Kosina <jkosina@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/1] uprobes: Kill __replace_page(), change
	uprobe_write_opcode() to rely on gup(WRITE)

On 12/10, Linus Torvalds wrote:
>
> On Tue, Dec 10, 2013 at 11:18 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > Well, if we use get_user_pages() we have vma for free.
>
> No we don't. get_user_pages() is expensive as hell.

I understand, I said "if we use get_user_pages()".

> We'd be *much* better off using get_user_pages_fast() if possible -
> and I bet _is_ possible in 99% of all cases.

We can't. get_user_pages_fast() takes mmap_sem.

Perhaps we can do something, say add FOLL_FAST_ONLY, but until then
we need the 1st get_user_pages(write => 0) anyway.

> > But I am not sure about "and verify it for now" above. Do you mean
> > that uprobe_write_opcode() should do another valid_vma() ?
>
> No. I think we should just do something like
>
>     if (vma->vm_flags & (VM_SHARED | VM_HUGETLB))
>         return -EINVAL;

OK, but WARN_ON(VM_SHARED | VM_HUGETLB) looks better imho. Because
this should not happen.

> then just looking up the page table _once_ - instead of
> three times - would make the code safer and faster.

Unlikely we can do this only once... At least I do not see how.

> It *may* be safe if callers do
> all the right black magic, but it's by no means obvious.

I agree, this needs more documentation in any case.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/