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

xen: fix is_xen_pmu()

is_xen_pmu() is taking the cpu number as parameter, but it is not using
it. Instead it just tests whether the Xen PMU initialization on the
current cpu did succeed. As this test is done by checking a percpu
pointer, preemption needs to be disabled in order to avoid switching
the cpu while doing the test. While resuming from suspend() this seems
not to be the case:

[   88.082751] ACPI: PM: Low-level resume complete
[   88.087933] ACPI: EC: EC started
[   88.091464] ACPI: PM: Restoring platform NVS memory
[   88.097166] xen_acpi_processor: Uploading Xen processor PM info
[   88.103850] Enabling non-boot CPUs ...
[   88.108128] installing Xen timer for CPU 1
[   88.112763] BUG: using smp_processor_id() in preemptible [00000000] code: systemd-sleep/7138
[   88.122256] caller is is_xen_pmu+0x12/0x30
[   88.126937] CPU: 0 PID: 7138 Comm: systemd-sleep Tainted: G        W         5.16.13-2.fc32.qubes.x86_64 #1
[   88.137939] Hardware name: Star Labs StarBook/StarBook, BIOS 7.97 03/21/2022
[   88.145930] Call Trace:
[   88.148757]  <TASK>
[   88.151193]  dump_stack_lvl+0x48/0x5e
[   88.155381]  check_preemption_disabled+0xde/0xe0
[   88.160641]  is_xen_pmu+0x12/0x30
[   88.164441]  xen_smp_intr_init_pv+0x75/0x100

Fix that by replacing is_xen_pmu() by a simple boolean variable which
reflects the Xen PMU initialization state on cpu 0.

Modify xen_pmu_init() to return early in case it is being called for a
cpu other than cpu 0 and the boolean variable not being set.

Rejected reason: This CVE ID has been rejected or withdrawn by its CVE Numbering Authority.

kernel.org: https://git.kernel.org/stable/c/26911a822148bef5dcfc55e7df49cb05a18737e3

kernel.org: https://git.kernel.org/stable/c/980bc42812c0a4788aee4b519bc911bfb911c23c

kernel.org: https://git.kernel.org/stable/c/ab2c789d1c0a3d0a682f7aa287754193471ff9f8

kernel.org: https://git.kernel.org/stable/c/af884b276b08e2b7e74c2b9208df35f36fa6a54c

kernel.org: https://git.kernel.org/stable/c/d533c4a2e8c4ca3a0fe84d295a7bd43af1931028

kernel.org: https://git.kernel.org/stable/c/de2ae403b4c0e79a3410e63bc448542fbb9f9bfc

kernel.org: https://git.kernel.org/stable/c/e9445a7a59d84ed3ae6c85f299d2a6c4930b1ee9

kernel.org: https://git.kernel.org/stable/c/e9f72105cf4a16bb185093b60fc12dbc82fe15b5