On Mon, Oct 16, 2017 at 2:18 PM, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote: > On 10/12/2017 03:53 PM, Boris Ostrovsky wrote: >> On 10/12/2017 03:27 PM, Andrew Cooper wrote: >>> On 12/10/17 20:11, Boris Ostrovsky wrote: >>>> There is also another problem: >>>> >>>> [ 1.312425] general protection fault: 0000 [#1] SMP >>>> [ 1.312901] Modules linked in: >>>> [ 1.313389] CPU: 0 PID: 1 Comm: init Not tainted 4.14.0-rc4+ #6 >>>> [ 1.313878] task: ffff88003e2c0000 task.stack: ffffc9000038c000 >>>> [ 1.314360] RIP: 10000e030:entry_SYSCALL_64_fastpath+0x1/0xa5 >>>> [ 1.314854] RSP: e02b:ffffc9000038ff50 EFLAGS: 00010046 >>>> [ 1.315336] RAX: 000000000000000c RBX: 000055f550168040 RCX: >>>> 00007fcfc959f59a >>>> [ 1.315827] RDX: 0000000000000000 RSI: 0000000000000000 RDI: >>>> 0000000000000000 >>>> [ 1.316315] RBP: 000000000000000a R08: 000000000000037f R09: >>>> 0000000000000064 >>>> [ 1.316805] R10: 000000001f89cbf5 R11: ffff88003e2c0000 R12: >>>> 00007fcfc958ad60 >>>> [ 1.317300] R13: 0000000000000000 R14: 000055f550185954 R15: >>>> 0000000000001000 >>>> [ 1.317801] FS: 0000000000000000(0000) GS:ffff88003f800000(0000) >>>> knlGS:0000000000000000 >>>> [ 1.318267] CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>> [ 1.318750] CR2: 00007fcfc97ab218 CR3: 000000003c88e000 CR4: >>>> 0000000000042660 >>>> [ 1.319235] Call Trace: >>>> [ 1.319700] Code: 51 50 57 56 52 51 6a da 41 50 41 51 41 52 41 53 48 >>>> 83 ec 30 65 4c 8b 1c 25 c0 d2 00 00 41 f7 03 df 39 08 90 0f 85 a5 00 00 >>>> 00 50 <ff> 15 9c 95 d0 ff 58 48 3d 4c 01 00 00 77 0f 4c 89 d1 ff 14 c5 >>>> [ 1.321161] RIP: entry_SYSCALL_64_fastpath+0x1/0xa5 RSP: ffffc9000038ff50 >>>> [ 1.344255] ---[ end trace d7cb8cd6cd7c294c ]--- >>>> [ 1.345009] Kernel panic - not syncing: Attempted to kill init! >>>> exitcode=0x0000000b >>>> >>>> >>>> All code >>>> ======== >>>> 0: 51 push %rcx >>>> 1: 50 push %rax >>>> 2: 57 push %rdi >>>> 3: 56 push %rsi >>>> 4: 52 push %rdx >>>> 5: 51 push %rcx >>>> 6: 6a da pushq $0xffffffffffffffda >>>> 8: 41 50 push %r8 >>>> a: 41 51 push %r9 >>>> c: 41 52 push %r10 >>>> e: 41 53 push %r11 >>>> 10: 48 83 ec 30 sub $0x30,%rsp >>>> 14: 65 4c 8b 1c 25 c0 d2 mov %gs:0xd2c0,%r11 >>>> 1b: 00 00 >>>> 1d: 41 f7 03 df 39 08 90 testl $0x900839df,(%r11) >>>> 24: 0f 85 a5 00 00 00 jne 0xcf >>>> 2a: 50 push %rax >>>> 2b:* ff 15 9c 95 d0 ff callq *-0x2f6a64(%rip) # >>>> 0xffffffffffd095cd <-- trapping instruction >>>> 31: 58 pop %rax >>>> 32: 48 3d 4c 01 00 00 cmp $0x14c,%rax >>>> 38: 77 0f ja 0x49 >>>> 3a: 4c 89 d1 mov %r10,%rcx >>>> 3d: ff .byte 0xff >>>> 3e: 14 c5 adc $0xc5,%al >>>> >>>> >>>> so the original 'cli' was replaced with the pv call but to me the offset >>>> looks a bit off, no? Shouldn't it always be positive? >>> callq takes a 32bit signed displacement, so jumping back by up to 2G is >>> perfectly legitimate. >> Yes, but >> >> ostr@workbase> nm vmlinux | grep entry_SYSCALL_64_fastpath >> ffffffff817365dd t entry_SYSCALL_64_fastpath >> ostr@workbase> nm vmlinux | grep " pv_irq_ops" >> ffffffff81c2dbc0 D pv_irq_ops >> ostr@workbase> >> >> so pv_irq_ops.irq_disable is about 5MB ahead of where we are now. (I >> didn't mean that x86 instruction set doesn't allow negative >> displacement, I was trying to say that pv_irq_ops always live further down) > > I believe the problem is this: > > #define PV_INDIRECT(addr) *addr(%rip) > > The displacement that the linker computes will be relative to the where > this instruction is placed at the time of linking, which is in > .pv_altinstructions (and not .text). So when we copy it into .text the > displacement becomes bogus. > > Replacing the macro with > > #define PV_INDIRECT(addr) *addr // well, it's not so much > indirect anymore > > makes things work. Or maybe it can be adjusted top be kept truly indirect. That is still an indirect call, just using absolute addressing for the pointer instead of RIP-relative. Alternatives has very limited relocation capabilities. It will only handle a single call or jmp replacement. Using absolute addressing is slightly less efficient (takes one extra byte to encode, and needs a relocation for KASLR), but it works just as well. You could also relocate the instruction manually by adding the delta between the original and replacement code to the displacement. -- Brian Gerst _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
