x86/alternatives: Exclude text poking against change_page_attr()

From time to time, the following BUG can be observed
in the x86 alternatives patching code [0]:

  > kernel BUG at arch/x86/kernel/alternative.c:2576!
  > Oops: invalid opcode: 0000 [#1] SMP NOPTI
  > CPU: 0 UID: 0 PID: 355 Comm: (udev-worker) Not tainted 7.1.3-1-default #1 PREEMPT(full) openSUSE Tumbleweed  8c1795b03ec64f997e57a8ad38b1161e3b98da64
  > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022
  > RIP: 0010:__text_poke+0x2aa/0x450
  > Call Trace:
  >  <TASK>
  >  smp_text_poke_batch_finish+0x2a7/0x320
  >  __static_call_transform+0xb7/0x220
  >  arch_static_call_transform+0x5b/0xb0
  >  __static_call_init+0xe9/0x270
  >  static_call_module_notify+0x11f/0x150
  >  notifier_call_chain+0x61/0xe0
  >  blocking_notifier_call_chain_robust+0x63/0xc0
  >  load_module+0x1c92/0x20c0
  >  init_module_from_file+0xd8/0x140
  >  idempotent_init_module+0x100/0x2f0
  >  __x64_sys_finit_module+0x71/0xe0
  >  do_syscall_64+0xe1/0x610
  >  entry_SYSCALL_64_after_hwframe+0x76/0x7e

which matches the following BUG_ON() in alternative.c:

	/*
	 * If something went wrong, crash and burn since recovery paths are not
	 * implemented.
	 */
	BUG_ON(!pages[0] || (cross_page_boundary && !pages[1]));

This can happen if vmalloc_to_page() fails, for any reason. Such can happen
if text poking races with CPA, which can possibly result in the collapsing
of page tables (or breaking of PMD hugepages). It is not a problem for most
users of vmalloc_to_page() (they solely own the vmalloc'd range) but, when
CONFIG_ARCH_HAS_EXECMEM_ROX=y, various modules own a single execmem vmalloc
range, and can call set_memory_*() in parallel on it. This can happen to
race against __text_poke and cause havoc in vmalloc_to_page().

Fix it by excluding against CPA using the init_mm mmap read lock.

[ dhansen: Fix up SoB ordering. The actual code flow here was:
	   Pedro=>Lorenzo=>Mike=>Me which is reflected in the SoB chain
	   now. I *believe* Mike simply picked up Lorenzo's update to
	   Pedro's post from the Link ]

Fixes: 64f6a4e10c05 ("x86: re-enable EXECMEM_ROX support")
Reported-by: Jiri Slaby <jirislaby@kernel.org>
Reported-by: Steffen Dirkwinkel <lists@steffen.cc>
Signed-off-by: Pedro Falcato <pfalcato@suse.de>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Co-developed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Jiri Slaby <jirislaby@kernel.org>
Tested-by: Atish Patra <atishp@meta.com>
Tested-by: Nikunj A Dadhania <nikunj@amd.com>
Cc: stable@vger.kernel.org
Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1271202 [0]
Link: https://lore.kernel.org/linux-mm/555ea1d43a12c30a8f1eaf10c899b3790d728f33.camel@dirkwinkel.cc/
Link: https://patch.msgid.link/20260813-cpa-fixes-v2-3-39b4ff90f91d@kernel.org

0 files changed, 0 insertions, 0 deletions