Messages in this thread | | | From | Richard Weinberger <> | Date | Fri, 14 Dec 2018 14:56:26 +0100 | Subject | Re: [PATCH v2] lzo: fix ip overrun during compress. |
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[CC'ing Kees]
On Wed, Dec 12, 2018 at 1:37 PM Markus F.X.J. Oberhumer <markus@oberhumer.com> wrote: > > I still claim that (0xfffffffffffff000, 4096) is not a valid C "pointer > to an object" according to the C standard - please see my reply below. > > And I thought ASLR was introduced to improve security and not to create > new security problems - someone from the ASLR team has to comment on this. > > Cheers, > Markus > > > On 2018-12-12 06:21, Yueyi Li wrote: > > Hi Markus, > > > > OK, thanks. I`ll change it in v3. > > > > Thanks, > > Yueyi > > > > On 2018/12/6 23:03, Markus F.X.J. Oberhumer wrote: > >> Hi Yueyi, > >> > >> yes, my LZO patch works for all cases. > >> > >> The reason behind the issue in the first place is that if KASLR > >> includes the very last page 0xfffffffffffff000 then we do not have a > >> valid C "pointer to an object" anymore because of address wraparound. > >> > >> Unrelated to my patch I'd argue that KASLR should *NOT* include the > >> very last page - indeed that might cause similar wraparound problems > >> in lots of code. > >> > >> Eg, look at this simple clear_memory() implementation: > >> > >> void clear_memory(char *p, size_t len) { > >> char *end = p + len; > >> while (p < end) > >> *p++= 0; > >> } > >> > >> Valid code like this will fail horribly when (p, len) is the very > >> last virtual page (because end will be the NULL pointer in this case). > >> > >> Cheers, > >> Markus > >> > >> > >> > >> On 2018-12-05 04:07, Yueyi Li wrote: > >>> Hi Markus, > >>> > >>> Thanks for your review. > >>> > >>> On 2018/12/4 18:20, Markus F.X.J. Oberhumer wrote: > >>>> Hi, > >>>> > >>>> I don't think that address space wraparound is legal in C, but I > >>>> understand that we are in kernel land and if you really want to > >>>> compress the last virtual page 0xfffffffffffff000 the following > >>>> small patch should fix that dubious case. > >>> I guess the VA 0xfffffffffffff000 is available because KASLR be > >>> enabled. For this case we can see: > >>> > >>> crash> kmem 0xfffffffffffff000 > >>> PAGE PHYSICAL MAPPING INDEX CNT FLAGS > >>> ffffffbfffffffc0 1fffff000 ffffffff1655ecb9 7181fd5 2 > >>> 8000000000064209 locked,uptodate,owner_priv_1,writeback,reclaim,swapbacked > >>> > >>>> This also avoids slowing down the the hot path of the compression > >>>> core function. > >>>> > >>>> Cheers, > >>>> Markus > >>>> > >>>> > >>>> > >>>> diff --git a/lib/lzo/lzo1x_compress.c b/lib/lzo/lzo1x_compress.c > >>>> index 236eb21167b5..959dec45f6fe 100644 > >>>> --- a/lib/lzo/lzo1x_compress.c > >>>> +++ b/lib/lzo/lzo1x_compress.c > >>>> @@ -224,8 +224,8 @@ int lzo1x_1_compress(const unsigned char *in, size_t in_len, > >>>> > >>>> while (l > 20) { > >>>> size_t ll = l <= (M4_MAX_OFFSET + 1) ? l : (M4_MAX_OFFSET + 1); > >>>> - uintptr_t ll_end = (uintptr_t) ip + ll; > >>>> - if ((ll_end + ((t + ll) >> 5)) <= ll_end) > >>>> + // check for address space wraparound > >>>> + if (((uintptr_t) ip + ll + ((t + ll) >> 5)) <= (uintptr_t) ip) > >>>> break; > >>>> BUILD_BUG_ON(D_SIZE * sizeof(lzo_dict_t) > LZO1X_1_MEM_COMPRESS); > >>>> memset(wrkmem, 0, D_SIZE * sizeof(lzo_dict_t)); > >>> I parsed panic ramdump and loaded CPU register values, can see: > >>> > >>> -000|lzo1x_1_do_compress( > >>> | in = 0xFFFFFFFFFFFFF000, > >>> | ?, > >>> | out = 0xFFFFFFFF2E2EE000, > >>> | out_len = 0xFFFFFF801CAA3510, > >>> | ?, > >>> | wrkmem = 0xFFFFFFFF4EBC0000) > >>> | dict = 0xFFFFFFFF4EBC0000 > >>> | op = 0x1 > >>> | ip = 0x9 > >>> | ii = 0x9 > >>> | in_end = 0x0 > >>> | ip_end = 0xFFFFFFFFFFFFFFEC > >>> | m_len = 0 > >>> | m_off = 1922 > >>> -001|lzo1x_1_compress( > >>> | in = 0xFFFFFFFFFFFFF000, > >>> | in_len = 0, > >>> | out = 0xFFFFFFFF2E2EE000, > >>> | out_len = 0x00000001616FB7D0, > >>> | wrkmem = 0xFFFFFFFF4EBC0000) > >>> | ip = 0xFFFFFFFFFFFFF000 > >>> | op = 0xFFFFFFFF2E2EE000 > >>> | l = 4096 > >>> | t = 0 > >>> | ll = 4096 > >>> > >>> ll = l = in_len = 4096 in lzo1x_1_compress, so your patch is working > >>> for this panic case, but, I`m > >>> not sure, is it possible that in = 0xFFFFFFFFFFFFF000 and in_len < 4096? > >>> > >>> > >>> Thanks, > >>> Yueyi > >>> > > > > > > -- > Markus Oberhumer, <markus@oberhumer.com>, http://www.oberhumer.com/
-- Thanks, //richard
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