Commit 517a97fc authored by Jann Horn's avatar Jann Horn Committed by Stephen Rothwell
Browse files

mmap locking API: don't check locking if the mm isn't live yet

In preparation for adding a mmap_assert_locked() check in
__get_user_pages(), teach the mmap_assert_*locked() helpers that it's fine
to operate on an mm without locking in the middle of execve() as long as
it hasn't been installed on a process yet.

Existing code paths that do this are (reverse callgraph):

  get_user_pages_remote
    get_arg_page
      copy_strings
      copy_string_kernel
      remove_arg_zero
    tomoyo_dump_page
      tomoyo_print_bprm
      tomoyo_scan_bprm
      tomoyo_environ

Link: https://lkml.kernel.org/r/CAG48ez03YJG9JU_6tGiMcaVjuTyRE_o4LEQ7901b5ZoCnNAjcg@mail.gmail.com

Signed-off-by: default avatarJann Horn <jannh@google.com>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarStephen Rothwell <sfr@canb.auug.org.au>
parent b9aed4a2
......@@ -1000,6 +1000,14 @@ static int exec_mmap(struct mm_struct *mm)
}
}
#if defined(CONFIG_LOCKDEP) || defined(CONFIG_DEBUG_VM)
/*
* From here on, the mm may be accessed concurrently, and proper locking
* is required for things like get_user_pages_remote().
*/
mm->mmap_lock_required = 1;
#endif
task_lock(tsk);
membarrier_exec_mmap(mm);
......
......@@ -561,6 +561,16 @@ struct mm_struct {
#ifdef CONFIG_IOMMU_SUPPORT
u32 pasid;
#endif
#if defined(CONFIG_LOCKDEP) || defined(CONFIG_DEBUG_VM)
/*
* Notes whether this mm has been installed on a process yet.
* If not, only the task going through execve() can access this
* mm, and no locking is needed around get_user_pages_remote().
* This flag is only used for debug checks.
*/
bool mmap_lock_required;
#endif
} __randomize_layout;
/*
......
......@@ -161,14 +161,22 @@ static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
static inline void mmap_assert_locked(struct mm_struct *mm)
{
lockdep_assert_held(&mm->mmap_lock);
VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
#if defined(CONFIG_LOCKDEP) || defined(CONFIG_DEBUG_VM)
if (mm->mmap_lock_required) {
lockdep_assert_held(&mm->mmap_lock);
VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
}
#endif
}
static inline void mmap_assert_write_locked(struct mm_struct *mm)
{
lockdep_assert_held_write(&mm->mmap_lock);
VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
#if defined(CONFIG_LOCKDEP) || defined(CONFIG_DEBUG_VM)
if (mm->mmap_lock_required) {
lockdep_assert_held_write(&mm->mmap_lock);
VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
}
#endif
}
static inline int mmap_lock_is_contended(struct mm_struct *mm)
......
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