From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
To: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Nick Piggin <npiggin@suse.de>,
LKML <linux-kernel@vger.kernel.org>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
Jim Keniston <jkenisto@us.ibm.com>,
systemtap-ml <systemtap@sources.redhat.com>,
"Frank Ch. Eigler" <fche@redhat.com>
Subject: Re: [BUG][kprobes][vunmap?]: kprobes may cause memory corruption
Date: Wed, 28 Jan 2009 13:10:53 -0500 [thread overview]
Message-ID: <20090128181053.GC9908@Krystal> (raw)
In-Reply-To: <49809CCE.40409@redhat.com>
* Masami Hiramatsu (mhiramat@redhat.com) wrote:
> Mathieu Desnoyers wrote:
> > * Masami Hiramatsu (mhiramat@redhat.com) wrote:
> >> Mathieu Desnoyers wrote:
> [...]
> >>> All this called in a loop. This would help isolating the "vmap" part of
> >>> the issue. If this test is not enough, then we should maybe try
> >>> something like this in a kernel module (which does what text_poke does
> >>> with vmalloc, more or less) in a loop :
> >>>
> >>> char somedata[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
> >>> char copydata[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
> >> Should both of them have PAGE_SIZE*2?
> >>
> >
> > Yes.
> >
> >>> void test_vmap(void)
> >>> }
> >>> struct page *pages[2];
> >>> char *vaddr;
> >>> int i;
> >>>
> >>> for (i = 0; i < 2 * PAGE_SIZE; i++)
> >>> copydata[i] = somedata[i];
> >>> page[0] = virt_to_page(&somedata);
> >>> BUG_ON(!page[0]);
> >>> page[1] = virt_to_page(&somedata + PAGE_SIZE);
> >>> BUG_ON(!page[1]);
>
> Oops, these should be vmalloc_to_page(), shouldn't it?
>
Yes, my bad. That should fix your oopses.
Mathieu
> >>> vaddr = vmap(pages, 2, VM_MAP, PAGE_KERNEL);
> >>> BUG_ON(!vaddr);
> >>>
> >>> for (i = 0; i < 2 * PAGE_SIZE; i++)
> >>> vaddr[i] = copydata[i] + 1;
> >>>
> >>> vunmap(vaddr);
> >>>
> >>> for (i = 0; i < 2 * PAGE_SIZE; i++)
> >>> BUG_ON(somedata[i] != copydata[i] + 1);
> >>> }
> >> Hmm, when I ran above code, it hit the last BUG_ON().
> >> I checked that somedata[i] didn't updated.
> >>
> >
> > Do you hit the BUG_ON after the first loop ?
>
> At the first loop, it hit the BUG_ON.
>
> >>> Given you don't seem to have hit the
> >>> for (i = 0; i < len; i++)
> >>> BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
> >>> test at the end of text_poke,
> >> However, when I ran kprobe-based test, it doesn't hit the BUG_ON()
> >> in text_poke().
> >>
> >
> > The variable declarations should have been 2*PAGE_SIZE, hopefully you
> > fixed them.
>
> Sure,
>
> > There is also a sync_core() in text_poke. It should not matter, but
> > maybe that could help ?
>
> Adding sync_core() could not help me... anyway, I'll try again
> with using vmalloc_to_page().
>
> >>> I suspect the write through the vmapped
> >>> area is correctly done, but that the problem may lay in the mm layer.
> >>> Maybe it's running out of pre-allocated vmap areas or something like
> >>> this ?
> >> I haven't seen vmalloc failure message on 2.6.29-rc2.
> >>
> >
> > It could be because the available vmalloc space is slightly higher.
> > Looking into the lazy vunmap threshold would be useful.
> >
> > You could also try with loop values higher than 400.
>
> OK, Thanks,
>
> --
> Masami Hiramatsu
>
> Software Engineer
> Hitachi Computer Products (America) Inc.
> Software Solutions Division
>
> e-mail: mhiramat@redhat.com
>
--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
next prev parent reply other threads:[~2009-01-28 18:11 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-28 2:32 [BUG][kprobes][vunmap?]: kprobes may cause memory corruption Masami Hiramatsu
2009-01-28 2:39 ` [PATCH][bugfix?][kprobes][vunmap?]: use vm_map_ram() in text_poke() Masami Hiramatsu
2009-01-28 5:09 ` [BUG][kprobes][vunmap?]: kprobes may cause memory corruption Masami Hiramatsu
2009-01-28 15:48 ` Mathieu Desnoyers
2009-01-28 16:22 ` Mathieu Desnoyers
2009-01-28 16:59 ` Masami Hiramatsu
2009-01-28 17:13 ` Mathieu Desnoyers
2009-01-28 17:58 ` Masami Hiramatsu
2009-01-28 18:10 ` Mathieu Desnoyers [this message]
2009-02-05 22:12 ` [BUGFIX][PATCH -rc/-mm] prevent kprobes from catching spurious page faults Masami Hiramatsu
2009-02-05 23:57 ` Ingo Molnar
2009-02-06 1:13 ` Mathieu Desnoyers
2009-02-06 2:04 ` Ingo Molnar
2009-02-06 2:05 ` Ingo Molnar
2009-02-06 16:30 ` Masami Hiramatsu
2009-02-06 15:57 ` Masami Hiramatsu
2009-03-16 22:57 ` [BUGFIX][PATCH] prevent boosting kprobes on exception address Masami Hiramatsu
2009-01-28 18:13 ` [BUG][kprobes][vunmap?]: kprobes may cause memory corruption Masami Hiramatsu
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