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Sean Christopherson 8819a49f9f KVM: x86: Unload "FPU" state on INIT if and only if its currently in-use 
Replace the hack added by commit f958bd2314 ("KVM: x86: Fix potential
put_fpu() w/o load_fpu() on MPX platform") with a more robust approach of
unloading+reloading guest FPU state based on whether or not the vCPU's FPU
is currently in-use, i.e. currently loaded.  This fixes a bug on hosts
that support CET but not MPX, where kvm_arch_vcpu_ioctl_get_mpstate()
neglects to load FPU state (it only checks for MPX support) and leads to
KVM attempting to put FPU state due to kvm_apic_accept_events() triggering
INIT emulation.  E.g. on a host with CET but not MPX, syzkaller+KASAN
generates:

  Oops: general protection fault, probably for non-canonical address 0xdffffc0000000004: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
  CPU: 211 UID: 0 PID: 20451 Comm: syz.9.26 Tainted: G S                  6.18.0-smp-DEV #7 NONE
  Tainted: [S]=CPU_OUT_OF_SPEC
  Hardware name: Google Izumi/izumi, BIOS 0.20250729.1-0 07/29/2025
  RIP: 0010:fpu_swap_kvm_fpstate+0x3ce/0x610 ../arch/x86/kernel/fpu/core.c:377
  RSP: 0018:ff1100410c167cc0 EFLAGS: 00010202
  RAX: 0000000000000004 RBX: 0000000000000020 RCX: 00000000000001aa
  RDX: 00000000000001ab RSI: ffffffff817bb960 RDI: 0000000022600000
  RBP: dffffc0000000000 R08: ff110040d23c8007 R09: 1fe220081a479000
  R10: dffffc0000000000 R11: ffe21c081a479001 R12: ff110040d23c8d98
  R13: 00000000fffdc578 R14: 0000000000000000 R15: ff110040d23c8d90
  FS:  00007f86dd1876c0(0000) GS:ff11007fc969b000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f86dd186fa8 CR3: 00000040d1dfa003 CR4: 0000000000f73ef0
  PKRU: 80000000
  Call Trace:
   <TASK>
   kvm_vcpu_reset+0x80d/0x12c0 ../arch/x86/kvm/x86.c:11818
   kvm_apic_accept_events+0x1cb/0x500 ../arch/x86/kvm/lapic.c:3489
   kvm_arch_vcpu_ioctl_get_mpstate+0xd0/0x4e0 ../arch/x86/kvm/x86.c:12145
   kvm_vcpu_ioctl+0x5e2/0xed0 ../virt/kvm/kvm_main.c:4539
   __se_sys_ioctl+0x11d/0x1b0 ../fs/ioctl.c:51
   do_syscall_x64 ../arch/x86/entry/syscall_64.c:63 [inline]
   do_syscall_64+0x6e/0x940 ../arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
  RIP: 0033:0x7f86de71d9c9
   </TASK>

with a very simple reproducer:

  r0 = openat$kvm(0xffffffffffffff9c, &(0x7f0000000000), 0x80b00, 0x0)
  r1 = ioctl$KVM_CREATE_VM(r0, 0xae01, 0x0)
  ioctl$KVM_CREATE_IRQCHIP(r1, 0xae60)
  r2 = ioctl$KVM_CREATE_VCPU(r1, 0xae41, 0x0)
  ioctl$KVM_SET_IRQCHIP(r1, 0x8208ae63, ...)
  ioctl$KVM_GET_MP_STATE(r2, 0x8004ae98, &(0x7f00000000c0))

Alternatively, the MPX hack in GET_MP_STATE could be extended to cover CET,
but from a "don't break existing functionality" perspective, that isn't any
less risky than peeking at the state of in_use, and it's far less robust
for a long term solution (as evidenced by this bug).

Reported-by: Alexander Potapenko <glider@google.com>
Fixes: 69cc3e8865 ("KVM: x86: Add XSS support for CET_KERNEL and CET_USER")
Reviewed-by: Yao Yuan <yaoyuan@linux.alibaba.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Link: https://patch.msgid.link/20251030185802.3375059-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
2025-11-04 09:14:11 -08:00
arch KVM: x86: Unload "FPU" state on INIT if and only if its currently in-use 2025-11-04 09:14:11 -08:00
block block-6.18-20251009 2025-10-10 10:37:13 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto This push contains the following changes: 2025-10-10 08:56:16 -07:00
Documentation KVM x86 fixes for 6.18: 2025-10-18 10:25:43 +02:00
drivers i2c-for-6.18-rc1-hotfix 2025-10-12 13:27:56 -07:00
fs - Avoid -Wflex-array-member-not-at-end warnings 2025-10-10 14:06:02 -07:00
include KVM x86 fixes for 6.18: 2025-10-18 10:25:43 +02:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring/zcrx: increment fallback loop src offset 2025-10-08 07:26:14 -06:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel tracing fixes for v6.18: 2025-10-11 16:06:04 -07:00
lib lib/test_kho: use kho_preserve_vmalloc instead of storing addresses in fdt 2025-10-07 13:48:56 -07:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm slab hotfix for 6.18-rc1 2025-10-11 10:40:24 -07:00
net bpf-fixes 2025-10-11 10:31:38 -07:00
rust 7 hotfixes. All 7 are cc:stable and all 7 are for MM. 2025-10-11 10:14:55 -07:00
samples Char/Misc/IIO/Binder changes for 6.18-rc1 2025-10-04 16:26:32 -07:00
scripts Kbuild fixes for 6.18 #1 2025-10-11 15:47:12 -07:00
security integrity-v6.18 2025-10-05 10:48:33 -07:00
sound sound fixes for 6.18-rc1 2025-10-10 09:55:19 -07:00
tools KVM x86 fixes for 6.18: 2025-10-18 10:25:43 +02:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM x86 fixes for 6.18: 2025-10-18 10:25:43 +02:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap MAINTAINERS, .mailmap: update Umang's email address 2025-10-07 13:48:55 -07:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING
CREDITS USB/Thunderbolt changes for 6.18-rc1 2025-10-04 16:07:08 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Just one series here - Mike Rappoport has taught KEXEC handover to 2025-10-11 10:27:52 -07:00
Makefile Linux 6.18-rc1 2025-10-12 13:42:36 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.