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Message-ID: <Pine.LNX.4.64.0710261247520.24322@blonde.wat.veritas.com> Date: Fri, 26 Oct 2007 13:02:57 +0100 (BST) From: Hugh Dickins <hugh@...itas.com> To: Jiri Kosina <jikos@...os.cz> cc: Sami Farin <safari-kernel@...ari.iki.fi>, Andrew Morton <akpm@...ux-foundation.org>, Linux kernel Mailing List <linux-kernel@...r.kernel.org>, Jiri Kosina <jkosina@...e.cz>, Arjan van de Ven <arjan@...radead.org> Subject: Re: [PATCH] [RFC] brk randomization: compute RLIMIT_DATA properly (was Re: x86: randomize brk() and RLIMIT_DATA) On Fri, 26 Oct 2007, Jiri Kosina wrote: > On Thu, 25 Oct 2007, Sami Farin wrote: > > > > > Would be neat if randomized brk and setrlimit(RLIMIT_DATA, ...) > > > > > worked in a predictable way: > > > > this isn't a valid case afaics; even on "traditional x86" (before we > > > > changed the address space layout, or even today if you have an > > > > unlimited stack rlimit) this isn't going to work. applications > > > > really shouldn't use (s)brk() but malloc(); you have to be able to > > > > fall back to mmap regardless of what you do. > > > I tend to agree here with Arjan. However it probably would make no > > > harm to make at least a little bit consisten behavior of setrlimit(), > > > though it has a little use in such cases. > > > Sami, does the patch below work for you? > > Thanks, Jiri, now RLIMIT_DATA works as expected. Using only RLIMIT_AS to > > limit processes' memory usage is not very easy. It includes also > > libraries mapped read-only, I have to check/modify the limits when I > > update/add libraries,... > > This patch is [RFC] as I am not sure whether it is worth it (see Arjan's > comment above). It is worth it. Arjan's right that RLIMIT_DATA has difficulty making sense, but you shouldn't be randomizing its breakage further with your patch. > > > From: Jiri Kosina <jkosina@...e.cz> > > brk randomization: compute RLIMIT_DATA properly > > In cases of heap area placed at randomly-generated offset from > mm->end_data (arch_randomize_brk()), we need to subtract the value of the > offset for setrlimit(RLIMIT_DATA) to work properly -- otherwise we count > the unoccupied memory between mm->end_data and mm->start_brk as occupied. > > Signed-off-by: Jiri Kosina <jkosina@...e.cz> > > diff --git a/mm/mmap.c b/mm/mmap.c > index facc1a7..c7ade18 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -251,7 +251,8 @@ asmlinkage unsigned long sys_brk(unsigned long brk) > * not page aligned -Ram Gupta > */ > rlim = current->signal->rlim[RLIMIT_DATA].rlim_cur; > - if (rlim < RLIM_INFINITY && brk - mm->start_data > rlim) > + if (rlim < RLIM_INFINITY && brk - mm->start_data - > + (mm->start_brk - mm->end_data) > rlim) > goto out; > > newbrk = PAGE_ALIGN(brk); I find the order in that test mysterious. Others might ask you to use an intermediate variable, I don't care about that, but I would find if (rlim < RLIM_INFINITY && (brk - mm->start_brk) + (mm->end_data - mm->start_data) > rlim) much easier to understand. Hugh - 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/
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