On Wed, Oct 27, 2021 at 1:35 PM Song Liu <[email protected]> wrote:
>
>
>
> > On Oct 27, 2021, at 12:52 PM, Yang Shi <[email protected]> wrote:
> >
> > The read-only THP for filesystems would collapse THP for file opened
> > readonly and mapped with VM_EXEC, the intended usecase is to avoid TLB
> > miss for large text segment. But it doesn't restrict the file types so
> > THP could be collapsed for non-regular file, for example, block device,
> > if it is opened readonly and mapped with EXEC permission. This may
> > cause bugs, like [1] and [2].
> >
> > This is definitely not intended usecase, so just collapsing THP for regular
> > file in order to close the attack surface.
> >
> > [1] https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+f5vA@mail.gmail.com/
> > [2] https://lore.kernel.org/linux-mm/[email protected]/
> >
> > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> > Reported-by: Hao Sun <[email protected]>
> > Reported-by: [email protected]
> > Cc: Hao Sun <[email protected]>
> > Cc: Matthew Wilcox <[email protected]>
> > Cc: Kirill A. Shutemov <[email protected]>
> > Cc: Song Liu <[email protected]>
> > Cc: Andrea Righi <[email protected]>
> > Cc: <[email protected]>
> > Signed-off-by: Hugh Dickins <[email protected]>
> > Signed-off-by: Yang Shi <[email protected]>
> > ---
> > The patch is basically based off the proposal from Hugh
> > (https://lore.kernel.org/linux-mm/[email protected]/).
> > It seems Hugh is too busy to prepare the patch for formal submission (I
> > didn't hear from him by pinging him a couple of times on mailing list),
> > so I prepared the patch and added his SOB.
> >
> > mm/khugepaged.c | 17 ++++++++++-------
> > 1 file changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index 045cc579f724..e91b7271275e 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
> > if (!transhuge_vma_enabled(vma, vm_flags))
> > return false;
> >
> > - /* Enabled via shmem mount options or sysfs settings. */
> > - if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {
> > + if (vma->vm_file)
> > return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
> > HPAGE_PMD_NR);
>
> Am I misreading this? If we return here for vma->vm_file, the following
> logic (shmem_file(), etc.) would be skipped, no?
Oh, yes, you are right. My mistake.
Andrew,
Could you please apply the below fix?
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index e91b7271275e..26f1798c88d2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -445,9 +445,9 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
if (!transhuge_vma_enabled(vma, vm_flags))
return false;
- if (vma->vm_file)
- return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
- HPAGE_PMD_NR);
+ if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
+ vma->vm_pgoff, HPAGE_PMD_NR))
+ return false;
/* Enabled via shmem mount options or sysfs settings. */
if (shmem_file(vma->vm_file))
>
> Thanks,
> Song
>
> > - }
> > +
> > + /* Enabled via shmem mount options or sysfs settings. */
> > + if (shmem_file(vma->vm_file))
> > + return shmem_huge_enabled(vma);
> >
> > /* THP settings require madvise. */
> > if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
> > return false;
> >
> > - /* Read-only file mappings need to be aligned for THP to work. */
> > + /* Only regular file is valid */
> > if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
> > - !inode_is_open_for_write(vma->vm_file->f_inode) &&
> > (vm_flags & VM_EXEC)) {
> > - return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
> > - HPAGE_PMD_NR);
> > + struct inode *inode = vma->vm_file->f_inode;
> > +
> > + return !inode_is_open_for_write(inode) &&
> > + S_ISREG(inode->i_mode);
> > }
> >
> > if (!vma->anon_vma || vma->vm_ops)
> > --
> > 2.26.2
> >
>
On Wed, 27 Oct 2021 13:44:37 -0700 Yang Shi <[email protected]> wrote:
> > > --- a/mm/khugepaged.c
> > > +++ b/mm/khugepaged.c
> > > @@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
> > > if (!transhuge_vma_enabled(vma, vm_flags))
> > > return false;
> > >
> > > - /* Enabled via shmem mount options or sysfs settings. */
> > > - if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {
> > > + if (vma->vm_file)
> > > return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
> > > HPAGE_PMD_NR);
> >
> > Am I misreading this? If we return here for vma->vm_file, the following
> > logic (shmem_file(), etc.) would be skipped, no?
>
> Oh, yes, you are right. My mistake.
>
> Andrew,
>
> Could you please apply the below fix?
um, how well tested are these changes?
On Wed, Oct 27, 2021 at 1:53 PM Andrew Morton <[email protected]> wrote:
>
> On Wed, 27 Oct 2021 13:44:37 -0700 Yang Shi <[email protected]> wrote:
>
> > > > --- a/mm/khugepaged.c
> > > > +++ b/mm/khugepaged.c
> > > > @@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
> > > > if (!transhuge_vma_enabled(vma, vm_flags))
> > > > return false;
> > > >
> > > > - /* Enabled via shmem mount options or sysfs settings. */
> > > > - if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {
> > > > + if (vma->vm_file)
> > > > return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
> > > > HPAGE_PMD_NR);
> > >
> > > Am I misreading this? If we return here for vma->vm_file, the following
> > > logic (shmem_file(), etc.) would be skipped, no?
> >
> > Oh, yes, you are right. My mistake.
> >
> > Andrew,
> >
> > Could you please apply the below fix?
>
> um, how well tested are these changes?
I has this fix on my test machine, but somehow forgot to fold it into
the original patch. The whole fix was tested by opening /dev/nullb0
readonly and mapping with PROT_EXEC, the THP was not collapsed
anymore.