| Message ID | 20211027195221.3825-1-shy828301@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: khugepaged: skip huge page collapse for special files | expand |
> On Oct 27, 2021, at 12:52 PM, Yang Shi <shy828301@gmail.com> 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/000000000000c6a82505ce284e4c@google.com/ > > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") > Reported-by: Hao Sun <sunhao.th@gmail.com> > Reported-by: syzbot+aae069be1de40fb11825@syzkaller.appspotmail.com > Cc: Hao Sun <sunhao.th@gmail.com> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Cc: Song Liu <songliubraving@fb.com> > Cc: Andrea Righi <andrea.righi@canonical.com> > Cc: <stable@vger.kernel.org> > Signed-off-by: Hugh Dickins <hughd@google.com> > Signed-off-by: Yang Shi <shy828301@gmail.com> > --- > The patch is basically based off the proposal from Hugh > (https://lore.kernel.org/linux-mm/a07564a3-b2fc-9ffe-3ace-3f276075ea5c@google.com/). > 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? 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, Oct 27, 2021 at 1:35 PM Song Liu <songliubraving@fb.com> wrote: > > > > > On Oct 27, 2021, at 12:52 PM, Yang Shi <shy828301@gmail.com> 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/000000000000c6a82505ce284e4c@google.com/ > > > > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") > > Reported-by: Hao Sun <sunhao.th@gmail.com> > > Reported-by: syzbot+aae069be1de40fb11825@syzkaller.appspotmail.com > > Cc: Hao Sun <sunhao.th@gmail.com> > > Cc: Matthew Wilcox <willy@infradead.org> > > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > Cc: Song Liu <songliubraving@fb.com> > > Cc: Andrea Righi <andrea.righi@canonical.com> > > Cc: <stable@vger.kernel.org> > > Signed-off-by: Hugh Dickins <hughd@google.com> > > Signed-off-by: Yang Shi <shy828301@gmail.com> > > --- > > The patch is basically based off the proposal from Hugh > > (https://lore.kernel.org/linux-mm/a07564a3-b2fc-9ffe-3ace-3f276075ea5c@google.com/). > > 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, Oct 27, 2021 at 12:52:21PM -0700, Yang Shi wrote: > +++ 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); > - } > + > + /* Enabled via shmem mount options or sysfs settings. */ > + if (shmem_file(vma->vm_file)) > + return shmem_huge_enabled(vma); This doesn't make sense to me. if vma->vm_file, we already returned, so this is dead code. > /* 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 <shy828301@gmail.com> 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 1:50 PM Matthew Wilcox <willy@infradead.org> wrote: > > On Wed, Oct 27, 2021 at 12:52:21PM -0700, Yang Shi wrote: > > +++ 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); > > - } > > + > > + /* Enabled via shmem mount options or sysfs settings. */ > > + if (shmem_file(vma->vm_file)) > > + return shmem_huge_enabled(vma); > > This doesn't make sense to me. if vma->vm_file, we already returned, > so this is dead code. Yes, Song mentioned the same thing. Fixed by an incremental patch. > > > /* 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, Oct 27, 2021 at 02:32:02PM -0700, Yang Shi wrote: > > This doesn't make sense to me. if vma->vm_file, we already returned, > > so this is dead code. > > Yes, Song mentioned the same thing. Fixed by an incremental patch. I saw that after I sent this. My email sometimes arrives slowly.
On Wed, Oct 27, 2021 at 1:53 PM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Wed, 27 Oct 2021 13:44:37 -0700 Yang Shi <shy828301@gmail.com> 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.
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); - } + + /* 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)
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/000000000000c6a82505ce284e4c@google.com/ Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Reported-by: Hao Sun <sunhao.th@gmail.com> Reported-by: syzbot+aae069be1de40fb11825@syzkaller.appspotmail.com Cc: Hao Sun <sunhao.th@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Song Liu <songliubraving@fb.com> Cc: Andrea Righi <andrea.righi@canonical.com> Cc: <stable@vger.kernel.org> Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Yang Shi <shy828301@gmail.com> --- The patch is basically based off the proposal from Hugh (https://lore.kernel.org/linux-mm/a07564a3-b2fc-9ffe-3ace-3f276075ea5c@google.com/). 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(-)