From: Baoquan He <bhe@redhat.com>
To: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: dyoung@redhat.com, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org, vgoyal@redhat.com,
kexec@lists.infradead.org, nasa4836@gmail.com, mhuang@redhat.com
Subject: Re: [PATCH V2] proc-vmcore: wrong data type casting fix
Date: Mon, 14 Mar 2016 11:50:53 +0800 [thread overview]
Message-ID: <20160314035053.GE2522@x1.redhat.com> (raw)
In-Reply-To: <20160314034722.GD2522@x1.redhat.com>
On 03/14/16 at 11:47am, Baoquan He wrote:
> On 03/14/16 at 12:25pm, HATAYAMA Daisuke wrote:
> > From: Dave Young <dyoung@redhat.com>
> > Subject: [PATCH V2] proc-vmcore: wrong data type casting fix
> > Date: Fri, 11 Mar 2016 16:42:48 +0800
> >
> > > On i686 PAE enabled machine the contiguous physical area could be large
> > > and it can cause trimming down variables in below calculation in
> > > read_vmcore() and mmap_vmcore():
> > >
> > > tsz = min_t(size_t, m->offset + m->size - *fpos, buflen);
> > >
> > > Then the real size passed down is not correct any more.
> > > Suppose m->offset + m->size - *fpos being truncated to 0, buflen >0 then
> >
> > That is, size_t and loff_t are defined as follows on i686:
> >
> > (gdb) ptype size_t
> > type = unsigned int
> > (gdb) ptype loff_t
> > type = long long int
> >
> > So casting by size_t means truncating a given value by 4GB.
> >
> > Then, if (m->offset + m->size - *fpos) is equal to or larger than 4GB,
> > and is aligned with 4GB, the resulted value is 0, and
>
> Truncating doesn't mean align. If (m->offset + m->size - *fpos) is
> larger than 4G, E.g 0x10000000f, the truncating result will be 0xf.
>
> >
> > > we will get tsz = 0. It is of course not an expected result.
>
> We won't always get "tsz=0", just get the lower 32 bit value.
OK, didn't get you still have saying in next paragraph. Ignore this
please.
>
> > >
> > > During our tests there are two problems caused by it:
> > > 1) read_vmcore will refuse to continue so makedumpfile fails.
> > > 2) mmap_vmcore will trigger BUG_ON() in remap_pfn_range().
> > >
> >
> > we reach these errors.
> >
> > If (m->offset + m->size - *fpos) is not aligned with 4GB,
> > read_vmcore() or mmap_vmcore() is performed with the truncated
> > non-zero value as size (of course, this is also not expected value but
> > the execution doesn't result in error). Then, fpos proceeds so that
> > (m->offset + m->size - *fpos) is aligned with 4GB in the next loop,
> > and we after all reach the errors.
> >
> > I think your patch description needs a bit more detail.
> >
> > It seems good to me that the patch itself.
> >
> > > Use unsigned long long in min_t instead so that the variables are not
> > > truncated.
> > >
> > > Signed-off-by: Baoquan He <bhe@redhat.com>
> > > Signed-off-by: Dave Young <dyoung@redhat.com>
> > > ---
> > > v1->v2: spelling fix in patch log
> > > fs/proc/vmcore.c | 7 +++++--
> > > 1 file changed, 5 insertions(+), 2 deletions(-)
> > >
> > > --- linux-x86.orig/fs/proc/vmcore.c
> > > +++ linux-x86/fs/proc/vmcore.c
> > > @@ -231,7 +231,9 @@ static ssize_t __read_vmcore(char *buffe
> > >
> > > list_for_each_entry(m, &vmcore_list, list) {
> > > if (*fpos < m->offset + m->size) {
> > > - tsz = min_t(size_t, m->offset + m->size - *fpos, buflen);
> > > + tsz = (size_t)min_t(unsigned long long,
> > > + m->offset + m->size - *fpos,
> > > + buflen);
> > > start = m->paddr + *fpos - m->offset;
> > > tmp = read_from_oldmem(buffer, tsz, &start, userbuf);
> > > if (tmp < 0)
> > > @@ -461,7 +463,8 @@ static int mmap_vmcore(struct file *file
> > > if (start < m->offset + m->size) {
> > > u64 paddr = 0;
> > >
> > > - tsz = min_t(size_t, m->offset + m->size - start, size);
> > > + tsz = (size_t)min_t(unsigned long long,
> > > + m->offset + m->size - start, size);
> > > paddr = m->paddr + start - m->offset;
> > > if (vmcore_remap_oldmem_pfn(vma, vma->vm_start + len,
> > > paddr >> PAGE_SHIFT, tsz,
> > >
> > --
> > Thanks.
> > HATAYAMA, Daisuke
next prev parent reply other threads:[~2016-03-14 3:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-11 8:42 [PATCH V2] proc-vmcore: wrong data type casting fix Dave Young
2016-03-11 20:27 ` Andrew Morton
2016-03-12 4:49 ` Dave Young
2016-03-12 12:43 ` Xunlei Pang
2016-03-12 13:59 ` Baoquan He
2016-03-13 6:11 ` Xunlei Pang
2016-03-14 2:41 ` Baoquan He
2016-03-14 3:25 ` HATAYAMA Daisuke
2016-03-14 3:31 ` Dave Young
2016-03-14 3:47 ` Baoquan He
2016-03-14 3:50 ` Baoquan He [this message]
2016-03-14 4:36 ` HATAYAMA Daisuke
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