On Tue 30-01-18 14:35:12, Michael Ellerman wrote: > Michal Hocko <mhocko@xxxxxxxxxx> writes: > > > On Mon 29-01-18 11:02:09, Anshuman Khandual wrote: > >> On 01/29/2018 08:17 AM, Anshuman Khandual wrote: > >> > On 01/26/2018 07:34 PM, Michal Hocko wrote: > >> >> On Fri 26-01-18 18:04:27, Anshuman Khandual wrote: > >> >> [...] > >> >>> I tried to instrument mmap_region() for a single instance of 'sed' > >> >>> binary and traced all it's VMA creation. But there is no trace when > >> >>> that 'anon' VMA got created which suddenly shows up during subsequent > >> >>> elf_map() call eventually failing it. Please note that the following > >> >>> VMA was never created through call into map_region() in the process > >> >>> which is strange. > ... > >> > >> Okay, this colliding VMA seems to be getting loaded from load_elf_binary() > >> function as well. > >> > >> [ 9.422410] vma c000001fceedbc40 start 0000000010030000 end 0000000010040000 > >> next c000001fceedbe80 prev c000001fceedb700 mm c000001fceea8200 > >> prot 8000000000000104 anon_vma (null) vm_ops (null) > >> pgoff 1003 file (null) private_data (null) > >> flags: 0x100073(read|write|mayread|maywrite|mayexec|account) > >> [ 9.422576] CPU: 46 PID: 7457 Comm: sed Not tainted 4.14.0-dirty #158 > >> [ 9.422610] Call Trace: > >> [ 9.422623] [c000001fdc4f79b0] [c000000000b17ac0] dump_stack+0xb0/0xf0 (unreliable) > >> [ 9.422670] [c000001fdc4f79f0] [c0000000002dafb8] do_brk_flags+0x2d8/0x440 > >> [ 9.422708] [c000001fdc4f7ac0] [c0000000002db3d0] vm_brk_flags+0x80/0x130 > >> [ 9.422747] [c000001fdc4f7b20] [c0000000003d23a4] set_brk+0x80/0xdc > >> [ 9.422785] [c000001fdc4f7b60] [c0000000003d1f24] load_elf_binary+0x1304/0x158c > >> [ 9.422830] [c000001fdc4f7c80] [c00000000035d3e0] search_binary_handler+0xd0/0x270 > >> [ 9.422881] [c000001fdc4f7d10] [c00000000035f338] do_execveat_common.isra.31+0x658/0x890 > >> [ 9.422926] [c000001fdc4f7df0] [c00000000035f980] SyS_execve+0x40/0x50 > >> [ 9.423588] [c000001fdc4f7e30] [c00000000000b220] system_call+0x58/0x6c > >> > >> which is getting hit after adding some more debug. > > > > Voila! So your binary simply overrides brk by elf segments. That sounds > > like the exactly the thing that the patch is supposed to protect from. > > Why this is the case I dunno. It is just clear that either brk or > > elf base are not put to the proper place. Something to get fixed. You > > are probably just lucky that brk allocations do not spil over to elf > > mappings. > > It is something to get fixed, but we can't retrospectively fix the > existing binaries sitting on peoples' systems. Yeah. Can we identify those somehow? Are they something people can easily come across? > Possibly powerpc arch code is doing something with the mmap layout or > something else that is confusing the ELF loader, in which case we should > fix that. Yes this definitely should be fixed. How can elf loader completely overlap brk mapping? > But if not then the only solution is for the ELF loader to be more > tolerant of this situation. > > So for 4.16 this patch either needs to be dropped, or reworked such that > powerpc can opt out of it. Yeah, let's hold on merging this until we understand what the heck is going on here. If this turnes to be unfixable I will think of a way for ppc to opt out. Anshuman, could you try to run sed 's@^@@' /proc/self/smaps on a system with MAP_FIXED_NOREPLACE reverted? -- Michal Hocko SUSE Labs
