CVE-2022-49557

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

x86/fpu: KVM: Set the base guest FPU uABI size to sizeof(struct kvm_xsave)

Set the starting uABI size of KVM's guest FPU to 'struct kvm_xsave',

i.e. to KVM's historical uABI size. When saving FPU state for usersapce,

KVM (well, now the FPU) sets the FP+SSE bits in the XSAVE header even if

the host doesn't support XSAVE. Setting the XSAVE header allows the VM

to be migrated to a host that does support XSAVE without the new host

having to handle FPU state that may or may not be compatible with XSAVE.

Setting the uABI size to the host's default size results in out-of-bounds

writes (setting the FP+SSE bits) and data corruption (that is thankfully

caught by KASAN) when running on hosts without XSAVE, e.g. on Core2 CPUs.

WARN if the default size is larger than KVM's historical uABI size; all

features that can push the FPU size beyond the historical size must be

opt-in.

==================================================================

BUG: KASAN: slab-out-of-bounds in fpu_copy_uabi_to_guest_fpstate+0x86/0x130

Read of size 8 at addr ffff888011e33a00 by task qemu-build/681

CPU: 1 PID: 681 Comm: qemu-build Not tainted 5.18.0-rc5-KASAN-amd64 #1

Hardware name: /DG35EC, BIOS ECG3510M.86A.0118.2010.0113.1426 01/13/2010

Call Trace:

<TASK>

dump_stack_lvl+0x34/0x45

print_report.cold+0x45/0x575

kasan_report+0x9b/0xd0

fpu_copy_uabi_to_guest_fpstate+0x86/0x130

kvm_arch_vcpu_ioctl+0x72a/0x1c50 [kvm]

kvm_vcpu_ioctl+0x47f/0x7b0 [kvm]

__x64_sys_ioctl+0x5de/0xc90

do_syscall_64+0x31/0x50

entry_SYSCALL_64_after_hwframe+0x44/0xae

</TASK>

Allocated by task 0:

(stack is not available)

The buggy address belongs to the object at ffff888011e33800

which belongs to the cache kmalloc-512 of size 512

The buggy address is located 0 bytes to the right of

512-byte region [ffff888011e33800, ffff888011e33a00)

The buggy address belongs to the physical page:

page:0000000089cd4adb refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11e30

head:0000000089cd4adb order:2 compound_mapcount:0 compound_pincount:0

flags: 0x4000000000010200(slab|head|zone=1)

raw: 4000000000010200 dead000000000100 dead000000000122 ffff888001041c80

raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff888011e33900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

ffff888011e33980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

>ffff888011e33a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

^

ffff888011e33a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

ffff888011e33b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

==================================================================

Disabling lock debugging due to kernel taint