| From e81434995081fd7efb755fd75576b35dbb0850b1 Mon Sep 17 00:00:00 2001 |
| From: Sean Christopherson <sean.j.christopherson@intel.com> |
| Date: Thu, 20 Dec 2018 14:21:08 -0800 |
| Subject: KVM: x86: Use jmp to invoke kvm_spurious_fault() from .fixup |
| |
| From: Sean Christopherson <sean.j.christopherson@intel.com> |
| |
| commit e81434995081fd7efb755fd75576b35dbb0850b1 upstream. |
| |
| ____kvm_handle_fault_on_reboot() provides a generic exception fixup |
| handler that is used to cleanly handle faults on VMX/SVM instructions |
| during reboot (or at least try to). If there isn't a reboot in |
| progress, ____kvm_handle_fault_on_reboot() treats any exception as |
| fatal to KVM and invokes kvm_spurious_fault(), which in turn generates |
| a BUG() to get a stack trace and die. |
| |
| When it was originally added by commit 4ecac3fd6dc2 ("KVM: Handle |
| virtualization instruction #UD faults during reboot"), the "call" to |
| kvm_spurious_fault() was handcoded as PUSH+JMP, where the PUSH'd value |
| is the RIP of the faulting instructing. |
| |
| The PUSH+JMP trickery is necessary because the exception fixup handler |
| code lies outside of its associated function, e.g. right after the |
| function. An actual CALL from the .fixup code would show a slightly |
| bogus stack trace, e.g. an extra "random" function would be inserted |
| into the trace, as the return RIP on the stack would point to no known |
| function (and the unwinder will likely try to guess who owns the RIP). |
| |
| Unfortunately, the JMP was replaced with a CALL when the macro was |
| reworked to not spin indefinitely during reboot (commit b7c4145ba2eb |
| "KVM: Don't spin on virt instruction faults during reboot"). This |
| causes the aforementioned behavior where a bogus function is inserted |
| into the stack trace, e.g. my builds like to blame free_kvm_area(). |
| |
| Revert the CALL back to a JMP. The changelog for commit b7c4145ba2eb |
| ("KVM: Don't spin on virt instruction faults during reboot") contains |
| nothing that indicates the switch to CALL was deliberate. This is |
| backed up by the fact that the PUSH <insn RIP> was left intact. |
| |
| Note that an alternative to the PUSH+JMP magic would be to JMP back |
| to the "real" code and CALL from there, but that would require adding |
| a JMP in the non-faulting path to avoid calling kvm_spurious_fault() |
| and would add no value, i.e. the stack trace would be the same. |
| |
| Using CALL: |
| |
| ------------[ cut here ]------------ |
| kernel BUG at /home/sean/go/src/kernel.org/linux/arch/x86/kvm/x86.c:356! |
| invalid opcode: 0000 [#1] SMP |
| CPU: 4 PID: 1057 Comm: qemu-system-x86 Not tainted 4.20.0-rc6+ #75 |
| Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 |
| RIP: 0010:kvm_spurious_fault+0x5/0x10 [kvm] |
| Code: <0f> 0b 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 55 49 89 fd 41 |
| RSP: 0018:ffffc900004bbcc8 EFLAGS: 00010046 |
| RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffffffffff |
| RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 |
| RBP: ffff888273fd8000 R08: 00000000000003e8 R09: 0000000000000000 |
| R10: 0000000000000000 R11: 0000000000000784 R12: ffffc90000371fb0 |
| R13: 0000000000000000 R14: 000000026d763cf4 R15: ffff888273fd8000 |
| FS: 00007f3d69691700(0000) GS:ffff888277800000(0000) knlGS:0000000000000000 |
| CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 |
| CR2: 000055f89bc56fe0 CR3: 0000000271a5a001 CR4: 0000000000362ee0 |
| Call Trace: |
| free_kvm_area+0x1044/0x43ea [kvm_intel] |
| ? vmx_vcpu_run+0x156/0x630 [kvm_intel] |
| ? kvm_arch_vcpu_ioctl_run+0x447/0x1a40 [kvm] |
| ? kvm_vcpu_ioctl+0x368/0x5c0 [kvm] |
| ? kvm_vcpu_ioctl+0x368/0x5c0 [kvm] |
| ? __set_task_blocked+0x38/0x90 |
| ? __set_current_blocked+0x50/0x60 |
| ? __fpu__restore_sig+0x97/0x490 |
| ? do_vfs_ioctl+0xa1/0x620 |
| ? __x64_sys_futex+0x89/0x180 |
| ? ksys_ioctl+0x66/0x70 |
| ? __x64_sys_ioctl+0x16/0x20 |
| ? do_syscall_64+0x4f/0x100 |
| ? entry_SYSCALL_64_after_hwframe+0x44/0xa9 |
| Modules linked in: vhost_net vhost tap kvm_intel kvm irqbypass bridge stp llc |
| ---[ end trace 9775b14b123b1713 ]--- |
| |
| Using JMP: |
| |
| ------------[ cut here ]------------ |
| kernel BUG at /home/sean/go/src/kernel.org/linux/arch/x86/kvm/x86.c:356! |
| invalid opcode: 0000 [#1] SMP |
| CPU: 6 PID: 1067 Comm: qemu-system-x86 Not tainted 4.20.0-rc6+ #75 |
| Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 |
| RIP: 0010:kvm_spurious_fault+0x5/0x10 [kvm] |
| Code: <0f> 0b 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 55 49 89 fd 41 |
| RSP: 0018:ffffc90000497cd0 EFLAGS: 00010046 |
| RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffffffffff |
| RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 |
| RBP: ffff88827058bd40 R08: 00000000000003e8 R09: 0000000000000000 |
| R10: 0000000000000000 R11: 0000000000000784 R12: ffffc90000369fb0 |
| R13: 0000000000000000 R14: 00000003c8fc6642 R15: ffff88827058bd40 |
| FS: 00007f3d7219e700(0000) GS:ffff888277900000(0000) knlGS:0000000000000000 |
| CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 |
| CR2: 00007f3d64001000 CR3: 0000000271c6b004 CR4: 0000000000362ee0 |
| Call Trace: |
| vmx_vcpu_run+0x156/0x630 [kvm_intel] |
| ? kvm_arch_vcpu_ioctl_run+0x447/0x1a40 [kvm] |
| ? kvm_vcpu_ioctl+0x368/0x5c0 [kvm] |
| ? kvm_vcpu_ioctl+0x368/0x5c0 [kvm] |
| ? __set_task_blocked+0x38/0x90 |
| ? __set_current_blocked+0x50/0x60 |
| ? __fpu__restore_sig+0x97/0x490 |
| ? do_vfs_ioctl+0xa1/0x620 |
| ? __x64_sys_futex+0x89/0x180 |
| ? ksys_ioctl+0x66/0x70 |
| ? __x64_sys_ioctl+0x16/0x20 |
| ? do_syscall_64+0x4f/0x100 |
| ? entry_SYSCALL_64_after_hwframe+0x44/0xa9 |
| Modules linked in: vhost_net vhost tap kvm_intel kvm irqbypass bridge stp llc |
| ---[ end trace f9daedb85ab3ddba ]--- |
| |
| Fixes: b7c4145ba2eb ("KVM: Don't spin on virt instruction faults during reboot") |
| Cc: stable@vger.kernel.org |
| Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> |
| Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/x86/include/asm/kvm_host.h | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/arch/x86/include/asm/kvm_host.h |
| +++ b/arch/x86/include/asm/kvm_host.h |
| @@ -1324,7 +1324,7 @@ asmlinkage void kvm_spurious_fault(void) |
| "cmpb $0, kvm_rebooting \n\t" \ |
| "jne 668b \n\t" \ |
| __ASM_SIZE(push) " $666b \n\t" \ |
| - "call kvm_spurious_fault \n\t" \ |
| + "jmp kvm_spurious_fault \n\t" \ |
| ".popsection \n\t" \ |
| _ASM_EXTABLE(666b, 667b) |
| |