WARNING in kvm_inject_emulated_page_fault

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: cb8e59cc Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14dedfe2100000
kernel config: https://syzkaller.appspot.com/x/.config?x=a16ddbc78955e3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=2a7156e11dc199bdbd8a
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=134ca2de100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=178272f2100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2a7156...@syzkaller.appspotmail.com

L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 6819 at arch/x86/kvm/x86.c:618 kvm_inject_emulated_page_fault+0x210/0x290 arch/x86/kvm/x86.c:618
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 6819 Comm: syz-executor268 Not tainted 5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x188/0x20d lib/dump_stack.c:118
panic+0x2e3/0x75c kernel/panic.c:221
__warn.cold+0x2f/0x35 kernel/panic.c:582
report_bug+0x27b/0x2f0 lib/bug.c:195
fixup_bug arch/x86/kernel/traps.c:105 [inline]
fixup_bug arch/x86/kernel/traps.c:100 [inline]
do_error_trap+0x12b/0x220 arch/x86/kernel/traps.c:197
do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:216
invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:kvm_inject_emulated_page_fault+0x210/0x290 arch/x86/kvm/x86.c:618
Code: 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 75 79 48 8b 53 08 4c 89 f6 48 89 ef e8 fa 04 0c 00 e9 10 ff ff ff e8 10 ac 68 00 <0f> 0b e9 3a fe ff ff 4c 89 e7 e8 21 74 a7 00 e9 5d fe ff ff 48 89
RSP: 0018:ffffc90000f87968 EFLAGS: 00010293
RAX: ffff888095202540 RBX: ffffc90000f879e0 RCX: ffffffff810ae417
RDX: 0000000000000000 RSI: ffffffff810ae5e0 RDI: 0000000000000001
RBP: ffff888088ce0040 R08: ffff888095202540 R09: fffff520001f0f58
R10: ffffc90000f87abf R11: fffff520001f0f57 R12: 0000000000000000
R13: 0000000000000001 R14: ffffc90000f87ab8 R15: ffff888088ce0380
nested_vmx_get_vmptr+0x1f9/0x2a0 arch/x86/kvm/vmx/nested.c:4638
handle_vmon arch/x86/kvm/vmx/nested.c:4767 [inline]
handle_vmon+0x168/0x3a0 arch/x86/kvm/vmx/nested.c:4728
vmx_handle_exit+0x29c/0x1260 arch/x86/kvm/vmx/vmx.c:6067
vcpu_enter_guest arch/x86/kvm/x86.c:8604 [inline]
vcpu_run arch/x86/kvm/x86.c:8669 [inline]
kvm_arch_vcpu_ioctl_run+0x2723/0x68a0 arch/x86/kvm/x86.c:8890
kvm_vcpu_ioctl+0x46a/0xe20 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3163
vfs_ioctl fs/ioctl.c:47 [inline]
ksys_ioctl+0x11a/0x180 fs/ioctl.c:771
__do_sys_ioctl fs/ioctl.c:780 [inline]
__se_sys_ioctl fs/ioctl.c:778 [inline]
__x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:778
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x443569
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 1b 0c fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffece6351a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffece6351b0 RCX: 0000000000443569
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000006
RBP: 0000000000000000 R08: 0000000020003800 R09: 0000000000400eb0
R10: 00007ffece633610 R11: 0000000000000246 R12: 0000000000404610
R13: 00000000004046a0 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Vitaly Kuznetsov]

syzbot <syzbot+2a7156...@syzkaller.appspotmail.com> writes:

> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: cb8e59cc Merge git://git.kernel.org/pub/scm/linux/kernel/g..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14dedfe2100000
> kernel config: https://syzkaller.appspot.com/x/.config?x=a16ddbc78955e3a9
> dashboard link: https://syzkaller.appspot.com/bug?extid=2a7156e11dc199bdbd8a
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=134ca2de100000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=178272f2100000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+2a7156...@syzkaller.appspotmail.com
>
> L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details.
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 6819 at arch/x86/kvm/x86.c:618
> kvm_inject_emulated_page_fault+0x210/0x290 arch/x86/kvm/x86.c:618

This is

WARN_ON_ONCE(fault->vector != PF_VECTOR);

[...]

Exception we're trying to inject comes from

nested_vmx_get_vmptr()
kvm_read_guest_virt()
kvm_read_guest_virt_helper()
vcpu->arch.walk_mmu->gva_to_gpa()

but it seems it is only set if GVA to GPA convertion fails. In case it
doesn't, we can still fail kvm_vcpu_read_guest_page() and return
X86EMUL_IO_NEEDED but nested_vmx_get_vmptr() doesn't case what we return
and does kvm_inject_emulated_page_fault(). This can happen when VMXON
parameter is MMIO, for example.

How do fix this? We can either properly exit to userspace for handling
or, if we decide that handling such requests makes little sense, just
inject #GP if exception is not set, e.g.

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 9c74a732b08d..a21e2f32f59b 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4635,7 +4635,11 @@ static int nested_vmx_get_vmptr(struct kvm_vcpu *vcpu, gpa_t *vmpointer)
return 1;

if (kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e)) {
- kvm_inject_emulated_page_fault(vcpu, &e);
+ if (e.vector == PF_VECTOR)
+ kvm_inject_emulated_page_fault(vcpu, &e);
+ else
+ kvm_inject_gp(vcpu, 0);
+
return 1;
}

--
Vitaly

[syzbot]

syzbot has bisected this bug to:

commit ee1fa209f5e5ca5c1e76c7aa1c2aab292f371f4a
Author: Junaid Shahid <jun...@google.com>
Date: Fri Mar 20 21:28:03 2020 +0000

KVM: x86: Sync SPTEs when injecting page/EPT fault into L1

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=138f49de100000
start commit: cb8e59cc Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: upstream
final crash: https://syzkaller.appspot.com/x/report.txt?x=104f49de100000
console output: https://syzkaller.appspot.com/x/log.txt?x=178f49de100000

kernel config: https://syzkaller.appspot.com/x/.config?x=a16ddbc78955e3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=2a7156e11dc199bdbd8a

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=134ca2de100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=178272f2100000

Reported-by: syzbot+2a7156...@syzkaller.appspotmail.com
Fixes: ee1fa209f5e5 ("KVM: x86: Sync SPTEs when injecting page/EPT fault into L1")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Paolo Bonzini]

Yes, this is a plausible fix (with a comment explaining that we are
taking a shortcut). Perhaps a better check would be

r = kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e);
if (r != X86EMUL_CONTINUE) {
if (r == X86EMUL_PROPAGATE_FAULT) {
kvm_inject_emulated_page_fault(vcpu, &e);
} else {
/* ... */
kvm_inject_gp(vcpu, 0);
}
return 1;
}

Are you going to send a patch?

Paolo

[Vitaly Kuznetsov]

Sure, will do.

--
Vitaly