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Vitaly Kuznetsov e47679c06a x86/hyperv: Properly deal with empty cpumasks in hyperv_flush_tlb_multi() 
[ Upstream commit 51500b71d5 ]

KASAN detected the following issue:

 BUG: KASAN: slab-out-of-bounds in hyperv_flush_tlb_multi+0xf88/0x1060
 Read of size 4 at addr ffff8880011ccbc0 by task kcompactd0/33

 CPU: 1 PID: 33 Comm: kcompactd0 Not tainted 5.14.0-39.el9.x86_64+debug #1
 Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine,
     BIOS Hyper-V UEFI Release v4.0 12/17/2019
 Call Trace:
  dump_stack_lvl+0x57/0x7d
  print_address_description.constprop.0+0x1f/0x140
  ? hyperv_flush_tlb_multi+0xf88/0x1060
  __kasan_report.cold+0x7f/0x11e
  ? hyperv_flush_tlb_multi+0xf88/0x1060
  kasan_report+0x38/0x50
  hyperv_flush_tlb_multi+0xf88/0x1060
  flush_tlb_mm_range+0x1b1/0x200
  ptep_clear_flush+0x10e/0x150
...
 Allocated by task 0:
  kasan_save_stack+0x1b/0x40
  __kasan_kmalloc+0x7c/0x90
  hv_common_init+0xae/0x115
  hyperv_init+0x97/0x501
  apic_intr_mode_init+0xb3/0x1e0
  x86_late_time_init+0x92/0xa2
  start_kernel+0x338/0x3eb
  secondary_startup_64_no_verify+0xc2/0xcb

 The buggy address belongs to the object at ffff8880011cc800
  which belongs to the cache kmalloc-1k of size 1024
 The buggy address is located 960 bytes inside of
  1024-byte region [ffff8880011cc800, ffff8880011ccc00)

'hyperv_flush_tlb_multi+0xf88/0x1060' points to
hv_cpu_number_to_vp_number() and '960 bytes' means we're trying to get
VP_INDEX for CPU#240. 'nr_cpus' here is exactly 240 so we're trying to
access past hv_vp_index's last element. This can (and will) happen
when 'cpus' mask is empty and cpumask_last() will return '>=nr_cpus'.

Commit ad0a6bad44 ("x86/hyperv: check cpu mask after interrupt has
been disabled") tried to deal with empty cpumask situation but
apparently didn't fully fix the issue.

'cpus' cpumask which is passed to hyperv_flush_tlb_multi() is
'mm_cpumask(mm)' (which is '&mm->cpu_bitmap'). This mask changes every
time the particular mm is scheduled/unscheduled on some CPU (see
switch_mm_irqs_off()), disabling IRQs on the CPU which is performing remote
TLB flush has zero influence on whether the particular process can get
scheduled/unscheduled on _other_ CPUs so e.g. in the case where the mm was
scheduled on one other CPU and got unscheduled during
hyperv_flush_tlb_multi()'s execution will lead to cpumask becoming empty.

It doesn't seem that there's a good way to protect 'mm_cpumask(mm)'
from changing during hyperv_flush_tlb_multi()'s execution. It would be
possible to copy it in the very beginning of the function but this is a
waste. It seems we can deal with changing cpumask just fine.

When 'cpus' cpumask changes during hyperv_flush_tlb_multi()'s
execution, there are two possible issues:
- 'Under-flushing': we will not flush TLB on a CPU which got added to
the mask while hyperv_flush_tlb_multi() was already running. This is
not a problem as this is equal to mm getting scheduled on that CPU
right after TLB flush.
- 'Over-flushing': we may flush TLB on a CPU which is already cleared
from the mask. First, extra TLB flush preserves correctness. Second,
Hyper-V's TLB flush hypercall takes 'mm->pgd' argument so Hyper-V may
avoid the flush if CR3 doesn't match.

Fix the immediate issue with cpumask_last()/hv_cpu_number_to_vp_number()
and remove the pointless cpumask_empty() check from the beginning of the
function as it really doesn't protect anything. Also, avoid the hypercall
altogether when 'flush->processor_mask' ends up being empty.

Fixes: ad0a6bad44 ("x86/hyperv: check cpu mask after interrupt has been disabled")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20220106094611.1404218-1-vkuznets@redhat.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-03-08 19:12:36 +01:00
arch x86/hyperv: Properly deal with empty cpumasks in hyperv_flush_tlb_multi() 2022-03-08 19:12:36 +01:00
block block-map: add __GFP_ZERO flag for alloc_page in function bio_copy_kern 2022-03-08 19:12:31 +01:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto crypto: api - Move cryptomgr soft dependency into algapi 2022-02-11 09:10:26 +01:00
Documentation tracing: Add ustring operation to filtering string pointers 2022-03-08 19:12:33 +01:00
drivers PCI: mvebu: Fix support for DEVCAP2, DEVCTL2 and LNKCTL2 registers on emulated bridge 2022-03-08 19:12:36 +01:00
fs nfsd: fix crash on COPY_NOTIFY with special stateid 2022-03-08 19:12:36 +01:00
include NFSD: Have legacy NFSD WRITE decoders use xdr_stream_subsegment() 2022-03-08 19:12:33 +01:00
init init: make unknown command line param message clearer 2021-11-18 19:17:11 +01:00
ipc ipc/sem: do not sleep with a spin lock held 2022-02-08 18:34:03 +01:00
kernel tracing: Do not let synth_events block other dyn_event systems during create 2022-03-08 19:12:35 +01:00
lib lib/iov_iter: initialize "flags" in new pipe_buffer 2022-02-23 12:03:20 +01:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm memblock: use kfree() to release kmalloced memblock regions 2022-03-02 11:48:10 +01:00
net NFSD: Have legacy NFSD WRITE decoders use xdr_stream_subsegment() 2022-03-08 19:12:33 +01:00
samples samples: bpf: Fix 'unknown warning group' build warning on Clang 2022-01-27 11:03:29 +01:00
scripts kconfig: fix failing to generate auto.conf 2022-02-23 12:03:20 +01:00
security selinux: fix misuse of mutex_is_locked() 2022-03-02 11:47:48 +01:00
sound ASoC: rt5682: do not block workqueue if card is unbound 2022-03-08 19:12:29 +01:00
tools tools/resolve_btf_ids: Close ELF file on error 2022-03-08 19:12:33 +01:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: s390: Ensure kvm_arch_no_poll() is read once when blocking vCPU 2022-03-08 19:12:34 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.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 drm fixes for 5.15 final 2021-10-28 12:17:01 -07:00
Makefile Linux 5.15.26 2022-03-02 11:48:10 +01:00
README

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.