Initialize debugfs_entry to its semi-magical -ENOENT value when the VM
is created. KVM's teardown when VM creation fails is kludgy and calls
kvm_uevent_notify_change() and kvm_destroy_vm_debugfs() even if KVM never
attempted kvm_create_vm_debugfs(). Because debugfs_entry is zero
initialized, the IS_ERR() checks pass and KVM derefs a NULL pointer.
BUG: kernel NULL pointer dereference, address: 0000000000000018
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 1068b1067 P4D 1068b1067 PUD 1068b0067 PMD 0
Oops: 0000 [#1] SMP
CPU: 0 PID: 871 Comm: repro Not tainted 5.18.0-rc1+ #825
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:__dentry_path+0x7b/0x130
Call Trace:
<TASK>
dentry_path_raw+0x42/0x70
kvm_uevent_notify_change.part.0+0x10c/0x200 [kvm]
kvm_put_kvm+0x63/0x2b0 [kvm]
kvm_dev_ioctl+0x43a/0x920 [kvm]
__x64_sys_ioctl+0x83/0xb0
do_syscall_64+0x31/0x50
entry_SYSCALL_64_after_hwframe+0x44/0xae
</TASK>
Modules linked in: kvm_intel kvm irqbypass
Fixes: a44a4cc1c969 ("KVM: Don't create VM debugfs files outside of the VM directory")
Cc: [email protected]
Cc: Marc Zyngier <[email protected]>
Cc: Oliver Upton <[email protected]>
Reported-by: [email protected]
Signed-off-by: Sean Christopherson <[email protected]>
---
virt/kvm/kvm_main.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index dfb7dabdbc63..d292c4397579 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -955,12 +955,6 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
int kvm_debugfs_num_entries = kvm_vm_stats_header.num_desc +
kvm_vcpu_stats_header.num_desc;
- /*
- * Force subsequent debugfs file creations to fail if the VM directory
- * is not created.
- */
- kvm->debugfs_dentry = ERR_PTR(-ENOENT);
-
if (!debugfs_initialized())
return 0;
@@ -1081,6 +1075,12 @@ static struct kvm *kvm_create_vm(unsigned long type)
BUILD_BUG_ON(KVM_MEM_SLOTS_NUM > SHRT_MAX);
+ /*
+ * Force subsequent debugfs file creations to fail if the VM directory
+ * is not created (by kvm_create_vm_debugfs()).
+ */
+ kvm->debugfs_dentry = ERR_PTR(-ENOENT);
+
if (init_srcu_struct(&kvm->srcu))
goto out_err_no_srcu;
if (init_srcu_struct(&kvm->irq_srcu))
base-commit: 150866cd0ec871c765181d145aa0912628289c8a
--
2.36.0.rc0.470.gd361397f0d-goog
Hi Sean,
On Thu, Apr 14, 2022 at 5:46 PM Sean Christopherson <[email protected]> wrote:
>
> Initialize debugfs_entry to its semi-magical -ENOENT value when the VM
> is created. KVM's teardown when VM creation fails is kludgy and calls
> kvm_uevent_notify_change() and kvm_destroy_vm_debugfs() even if KVM never
> attempted kvm_create_vm_debugfs(). Because debugfs_entry is zero
Boo! I've got a few patches to bring kvm_create_vm_debugfs() in line
with the rest of the VM initialization. Kinda gross it is done in the
ioctl body.
> initialized, the IS_ERR() checks pass and KVM derefs a NULL pointer.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000018
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 1068b1067 P4D 1068b1067 PUD 1068b0067 PMD 0
> Oops: 0000 [#1] SMP
> CPU: 0 PID: 871 Comm: repro Not tainted 5.18.0-rc1+ #825
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
> RIP: 0010:__dentry_path+0x7b/0x130
> Call Trace:
> <TASK>
> dentry_path_raw+0x42/0x70
> kvm_uevent_notify_change.part.0+0x10c/0x200 [kvm]
> kvm_put_kvm+0x63/0x2b0 [kvm]
> kvm_dev_ioctl+0x43a/0x920 [kvm]
> __x64_sys_ioctl+0x83/0xb0
> do_syscall_64+0x31/0x50
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> </TASK>
> Modules linked in: kvm_intel kvm irqbypass
>
> Fixes: a44a4cc1c969 ("KVM: Don't create VM debugfs files outside of the VM directory")
> Cc: [email protected]
> Cc: Marc Zyngier <[email protected]>
> Cc: Oliver Upton <[email protected]>
> Reported-by: [email protected]
> Signed-off-by: Sean Christopherson <[email protected]>
Looks good, grats to the bots for finding my dirty laundry.
Reviewed-by: Oliver Upton <[email protected]>
Queued, thanks.
Paolo