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Sean Christopherson 155ec243ef KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding 
[ Upstream commit fc3ba56385 ]

Drop the WARN in svm_set_nested_state() on nested_svm_load_cr3() failing
as it is trivially easy to trigger from userspace by modifying CPUID after
loading CR3.  E.g. modifying the state restoration selftest like so:

  --- tools/testing/selftests/kvm/x86/state_test.c
  +++ tools/testing/selftests/kvm/x86/state_test.c
  @@ -280,7 +280,16 @@ int main(int argc, char *argv[])

                 /* Restore state in a new VM.  */
                  vcpu = vm_recreate_with_one_vcpu(vm);
  -               vcpu_load_state(vcpu, state);
  +
  +               if (stage == 4) {
  +                       state->sregs.cr3 = BIT(44);
  +                       vcpu_load_state(vcpu, state);
  +
  +                       vcpu_set_cpuid_property(vcpu, X86_PROPERTY_MAX_PHY_ADDR, 36);
  +                       __vcpu_nested_state_set(vcpu, &state->nested);
  +               } else {
  +                       vcpu_load_state(vcpu, state);
  +               }

                  /*
                   * Restore XSAVE state in a dummy vCPU, first without doing

generates:

  WARNING: CPU: 30 PID: 938 at arch/x86/kvm/svm/nested.c:1877 svm_set_nested_state+0x34a/0x360 [kvm_amd]
  Modules linked in: kvm_amd kvm irqbypass [last unloaded: kvm]
  CPU: 30 UID: 1000 PID: 938 Comm: state_test Tainted: G        W           6.18.0-rc7-58e10b63777d-next-vm
  Tainted: [W]=WARN
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:svm_set_nested_state+0x34a/0x360 [kvm_amd]
  Call Trace:
   <TASK>
   kvm_arch_vcpu_ioctl+0xf33/0x1700 [kvm]
   kvm_vcpu_ioctl+0x4e6/0x8f0 [kvm]
   __x64_sys_ioctl+0x8f/0xd0
   do_syscall_64+0x61/0xad0
   entry_SYSCALL_64_after_hwframe+0x4b/0x53

Simply delete the WARN instead of trying to prevent userspace from shoving
"illegal" state into CR3.  For better or worse, KVM's ABI allows userspace
to set CPUID after SREGS, and vice versa, and KVM is very permissive when
it comes to guest CPUID.  I.e. attempting to enforce the virtual CPU model
when setting CPUID could break userspace.  Given that the WARN doesn't
provide any meaningful protection for KVM or benefit for userspace, simply
drop it even though the odds of breaking userspace are minuscule.

Opportunistically delete a spurious newline.

Fixes: b222b0b881 ("KVM: nSVM: refactor the CR3 reload on migration")
Cc: stable@vger.kernel.org
Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20251216161755.1775409-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-03-04 07:20:25 -05:00
arch KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding 2026-03-04 07:20:25 -05:00
block blk-mq-debugfs: add missing debugfs_mutex in blk_mq_debugfs_register_hctxs() 2026-03-04 07:19:59 -05:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-02-06 16:41:53 +01:00
Documentation PCI: endpoint: Automatically create a function specific attributes group 2026-02-19 16:21:46 +01:00
drivers media: mtk-mdp: Fix a reference leak bug in mtk_mdp_remove() 2026-03-04 07:20:25 -05:00
fs btrfs: replace BUG() with error handling in __btrfs_balance() 2026-03-04 07:20:21 -05:00
include Bluetooth: L2CAP: Fix invalid response to L2CAP_ECRED_RECONF_REQ 2026-03-04 07:20:22 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:21:45 +02:00
io_uring io_uring: fix filename leak in __io_openat_prep() 2026-01-19 13:09:54 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:05:26 +01:00
kernel tracing: Fix false sharing in hwlat get_sample() 2026-03-04 07:20:14 -05:00
lib lib/crypto: aes: Fix missing MMU protection for AES S-box 2026-01-19 13:10:13 +01:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/kfence: randomize the freelist on initialization 2026-02-11 13:35:27 +01:00
net netfilter: nf_conntrack_h323: fix OOB read in decode_choice() 2026-03-04 07:20:25 -05:00
samples samples: mei: Fix building on musl libc 2025-08-28 16:24:07 +02:00
scripts modpost: Amend ppc64 save/restfpr symnames for -Os build 2026-03-04 07:20:06 -05:00
security apparmor: fix invalid deref of rawdata when export_binary is unset 2026-03-04 07:19:53 -05:00
sound ALSA: usb-audio: Add sanity check for OOB writes at silencing 2026-03-04 07:20:20 -05:00
tools tools/power cpupower: Reset errno before strtoull() 2026-03-04 07:19:57 -05:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:05:22 +01:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-02-11 13:35:27 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:09:36 +09:00
Makefile Linux 5.15.201 2026-02-19 16:21:47 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 Restructured Text 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.