AZL-99062

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86/mmu: WARN and clear role.invalid when creating a child shadow page

Explicitly clear role.invalid when deriving a child shadow page's role from its parent to harden against bugs elsewhere in KVM, as violating KVM's invariant that invalid pages are NOT on the list of active MMU pages leads to use-after-free due to __kvmmmupreparezappage() using listadd() instead of listmove() when processing an invalid shadow page, i.e. makes a bad situation far worse.

Yell loudly if the parent is invalid, as it means KVM has missed a validity check, i.e. KVM is attempting to map memory using an invalid/obsolete root, but continue on as the child is otherwise still a valid shadow page.

================================================================== BUG: KASAN: slab-use-after-free in __kvmmmugetshadowpage+0x1817/0x1860 [kvm] Write of size 8 at addr ff11000153dd1368 by task repro/853

CPU: 1 UID: 1000 PID: 853 Comm: repro Not tainted 7.2.0-rc2-3aec122bdcaf-next-vm #5 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: <TASK> dumpstacklvl+0x4b/0x70 printreport+0x153/0x49c kasanreport+0xbc/0xf0 __kvmmmugetshadowpage+0x1817/0x1860 [kvm] mmuallocroot+0x141/0x320 [kvm] kvmmmuload+0x612/0x20f0 [kvm] kvmarchvcpuioctlrun+0x3dd5/0x6150 [kvm] kvmvcpuioctl+0x5e4/0x10d0 [kvm] __x64sysioctl+0x131/0x1b0 dosyscall64+0x67/0x5f0 entrySYSCALL64afterhwframe+0x4b/0x53 </TASK>

Allocated by task 853: kasansavestack+0x20/0x40 kasansavetrack+0x14/0x30 __kasanslaballoc+0x5f/0x70 kmem_cacheallocnoprof+0xfe/0x2e0 __kvmmmutopup_memorycache+0x135/0x530 [kvm] paging64pagefault+0x318/0x1e30 [kvm] kvmmmudopagefault+0x21d/0x630 [kvm] kvmmmupagefault+0x18c/0x17b0 [kvm] kvmarchvcpuioctlrun+0x1f35/0x6150 [kvm] kvmvcpuioctl+0x5e4/0x10d0 [kvm] __x64sysioctl+0x131/0x1b0 dosyscall64+0x67/0x5f0 entrySYSCALL64afterhwframe+0x4b/0x53

Freed by task 853: kasansavestack+0x20/0x40 kasansavetrack+0x14/0x30 kasansavefree_info+0x3b/0x60 __kasanslabfree+0x43/0x70 kmemcachefree+0xe2/0x400 kvmmmucommitzappage.part.0+0x1e2/0x310 [kvm] kvmmmufreeroots+0x283/0x560 [kvm] kvmarchvcpuioctlrun+0x33c8/0x6150 [kvm] kvmvcpu_ioctl+0x5e4/0x10d0 [kvm] __x64sysioctl+0x131/0x1b0 dosyscall64+0x67/0x5f0 entrySYSCALL64afterhwframe+0x4b/0x53