On Fri, Aug 28, 2020 at 12:14:28PM +1000, Michael Ellerman wrote: > Dmitry Safonov <0x7f454c46@xxxxxxxxx> writes: > > On Wed, 26 Aug 2020 at 15:39, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote: > >> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes: > >> We added a test for vdso unmap recently because it happened to trigger a > >> KAUP failure, and someone actually hit it & reported it. > > > > You right, CRIU cares much more about moving vDSO. > > It's done for each restoree and as on most setups vDSO is premapped and > > used by the application - it's actively tested. > > Speaking about vDSO unmap - that's concerning only for heterogeneous C/R, > > i.e when an application is migrated from a system that uses vDSO to the one > > which doesn't - it's much rare scenario. > > (for arm it's !CONFIG_VDSO, for x86 it's `vdso=0` boot parameter) > > Ah OK that explains it. > > The case we hit of VDSO unmapping was some strange "library OS" thing > which had explicitly unmapped the VDSO, so also very rare. > > > Looking at the code, it seems quite easy to provide/maintain .close() for > > vm_special_mapping. A bit harder to add a test from CRIU side > > (as glibc won't know on restore that it can't use vdso anymore), > > but totally not impossible. > > > >> Running that test on arm64 segfaults: > >> > >> # ./sigreturn_vdso > >> VDSO is at 0xffff8191f000-0xffff8191ffff (4096 bytes) > >> Signal delivered OK with VDSO mapped > >> VDSO moved to 0xffff8191a000-0xffff8191afff (4096 bytes) > >> Signal delivered OK with VDSO moved > >> Unmapped VDSO > >> Remapped the stack executable > >> [ 48.556191] potentially unexpected fatal signal 11. > >> [ 48.556752] CPU: 0 PID: 140 Comm: sigreturn_vdso Not tainted 5.9.0-rc2-00057-g2ac69819ba9e #190 > >> [ 48.556990] Hardware name: linux,dummy-virt (DT) > >> [ 48.557336] pstate: 60001000 (nZCv daif -PAN -UAO BTYPE=--) > >> [ 48.557475] pc : 0000ffff8191a7bc > >> [ 48.557603] lr : 0000ffff8191a7bc > >> [ 48.557697] sp : 0000ffffc13c9e90 > >> [ 48.557873] x29: 0000ffffc13cb0e0 x28: 0000000000000000 > >> [ 48.558201] x27: 0000000000000000 x26: 0000000000000000 > >> [ 48.558337] x25: 0000000000000000 x24: 0000000000000000 > >> [ 48.558754] x23: 0000000000000000 x22: 0000000000000000 > >> [ 48.558893] x21: 00000000004009b0 x20: 0000000000000000 > >> [ 48.559046] x19: 0000000000400ff0 x18: 0000000000000000 > >> [ 48.559180] x17: 0000ffff817da300 x16: 0000000000412010 > >> [ 48.559312] x15: 0000000000000000 x14: 000000000000001c > >> [ 48.559443] x13: 656c626174756365 x12: 7865206b63617473 > >> [ 48.559625] x11: 0000000000000003 x10: 0101010101010101 > >> [ 48.559828] x9 : 0000ffff818afda8 x8 : 0000000000000081 > >> [ 48.559973] x7 : 6174732065687420 x6 : 64657070616d6552 > >> [ 48.560115] x5 : 000000000e0388bd x4 : 000000000040135d > >> [ 48.560270] x3 : 0000000000000000 x2 : 0000000000000001 > >> [ 48.560412] x1 : 0000000000000003 x0 : 00000000004120b8 > >> Segmentation fault > >> # > >> > >> So I think we need to keep the unmap hook. Maybe it should be handled by > >> the special_mapping stuff generically. > > > > I'll cook a patch for vm_special_mapping if you don't mind :-) > > That would be great, thanks! I lost track of this one. Is there a patch kicking around to resolve this, or is the segfault expected behaviour? Will
