Messages in this thread Patch in this message | | | Subject | Re: [PATCH v2] lzo: fix ip overrun during compress. | From | "Markus F.X.J. Oberhumer" <> | Date | Wed, 12 Dec 2018 13:35:15 +0100 |
| |
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/
| |