[17/19] mm/secretmem: fix NULL page->mapping dereference in page_is_secretmem()

Commit Message

Andrew Morton Oct. 18, 2021, 10:16 p.m. UTC

From: Sean Christopherson <[e-mail]>
Subject: mm/secretmem: fix NULL page->mapping dereference in page_is_secretmem()

Check for a NULL page->mapping before dereferencing the mapping in
page_is_secretmem(), as the page's mapping can be nullified while gup() is
running, e.g.  by reclaim or truncation.

  BUG: kernel NULL pointer dereference, address: 0000000000000068
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] PREEMPT SMP NOPTI
  CPU: 6 PID: 4173897 Comm: CPU 3/KVM Tainted: G        W
  RIP: 0010:internal_get_user_pages_fast+0x621/0x9d0
  Code: <48> 81 7a 68 80 08 04 bc 0f 85 21 ff ff 8 89 c7 be
  RSP: 0018:ffffaa90087679b0 EFLAGS: 00010046
  RAX: ffffe3f37905b900 RBX: 00007f2dd561e000 RCX: ffffe3f37905b934
  RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffe3f37905b900
  ...
  CR2: 0000000000000068 CR3: 00000004c5898003 CR4: 00000000001726e0
  Call Trace:
   get_user_pages_fast_only+0x13/0x20
   hva_to_pfn+0xa9/0x3e0
   try_async_pf+0xa1/0x270
   direct_page_fault+0x113/0xad0
   kvm_mmu_page_fault+0x69/0x680
   vmx_handle_exit+0xe1/0x5d0
   kvm_arch_vcpu_ioctl_run+0xd81/0x1c70
   kvm_vcpu_ioctl+0x267/0x670
   __x64_sys_ioctl+0x83/0xa0
   do_syscall_64+0x56/0x80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas")
Signed-off-by: Sean Christopherson <[e-mail]>
Reported-by: Darrick J. Wong <[e-mail]>
Reported-by: Stephen <[e-mail]>
Tested-by: Darrick J. Wong <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Reviewed-by: Mike Rapoport <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/secretmem.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

--- a/include/linux/secretmem.h~mm-fix-null-page-mapping-dereference-in-page_is_secretmem
+++ a/include/linux/secretmem.h
@@ -23,7 +23,7 @@  static inline bool page_is_secretmem(str
 	mapping = (struct address_space *)
 		((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS);
 
-	if (mapping != page->mapping)
+	if (!mapping || mapping != page->mapping)
 		return false;
 
 	return mapping->a_ops == &secretmem_aops;