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Sean Christopherson 969e5e13ff 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 07:20:59 -05:00
arch KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding 2026-03-04 07:20:59 -05:00
block block: decouple secure erase size limit from discard size limit 2026-03-04 07:19:38 -05:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-30 10:32:12 +01:00
Documentation ipv6: Move ipv6_fl_list from ipv6_pinfo to inet_sock. 2026-03-04 07:20:44 -05:00
drivers media: verisilicon: AV1: Fix tx mode bit setting 2026-03-04 07:20:58 -05:00
fs hfsplus: ensure sb->s_fs_info is always cleaned up 2026-03-04 07:20:53 -05:00
include drm/tests: shmem: Hold reservation lock around purge 2026-03-04 07:20:55 -05:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring/timeout: annotate data race in io_flush_timeouts() 2026-03-04 07:19:36 -05:00
ipc ipc: don't audit capability check in ipc_permissions() 2026-02-26 14:59:19 -08:00
kernel Remove WARN_ALL_UNSEEDED_RANDOM kernel config option 2026-03-04 07:20:46 -05:00
lib Remove WARN_ALL_UNSEEDED_RANDOM kernel config option 2026-03-04 07:20:46 -05:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm mm/slab: fix false lockdep warning in __kfree_rcu_sheaf() 2026-02-26 14:59:14 -08:00
net netfilter: nf_conntrack_h323: fix OOB read in decode_choice() 2026-03-04 07:20:52 -05:00
rust rust: cpufreq: always inline functions using build_assert with arguments 2026-03-04 07:19:37 -05:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:17:11 +01:00
scripts modpost: Amend ppc64 save/restfpr symnames for -Os build 2026-03-04 07:20:07 -05:00
security apparmor: fix aa_label to return state from compount and component match 2026-02-26 14:59:42 -08:00
sound ASoC: SOF: ipc4-control: Keep the payload size up to date 2026-03-04 07:20:54 -05:00
tools rtla: Fix NULL pointer dereference in actions_parse 2026-03-04 07:20:13 -05:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-02-11 13:41:44 +01:00
.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 scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.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 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
.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 COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -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 soc: fixes for 6.18, part 4 2025-11-28 09:57:31 -08:00
Makefile Linux 6.18.15 2026-02-27 16:05:10 -05:00
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.