[v2,4/6] mm: replace vma->vm_flags indirect modification in ksm_madvise
Commit Message
Replace indirect modifications to vma->vm_flags with calls to modifier
functions to be able to track flag changes and to keep vma locking
correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
vm_flags modification attempts.
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
arch/s390/mm/gmap.c | 5 ++++-
mm/khugepaged.c | 2 ++
mm/ksm.c | 2 ++
4 files changed, 12 insertions(+), 2 deletions(-)
Comments
On Wed 25-01-23 00:38:49, Suren Baghdasaryan wrote:
> Replace indirect modifications to vma->vm_flags with calls to modifier
> functions to be able to track flag changes and to keep vma locking
> correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
> vm_flags modification attempts.
Those BUG_ONs scream to much IMHO. KSM is an MM internal code so I
gueess we should be willing to trust it.
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
On Wed, Jan 25, 2023 at 1:38 AM 'Michal Hocko' via kernel-team
<kernel-team@android.com> wrote:
>
> On Wed 25-01-23 00:38:49, Suren Baghdasaryan wrote:
> > Replace indirect modifications to vma->vm_flags with calls to modifier
> > functions to be able to track flag changes and to keep vma locking
> > correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
> > vm_flags modification attempts.
>
> Those BUG_ONs scream to much IMHO. KSM is an MM internal code so I
> gueess we should be willing to trust it.
Yes, but I really want to prevent an indirect misuse since it was not
easy to find these. If you feel strongly about it I will remove them
or if you have a better suggestion I'm all for it.
>
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
>
> Acked-by: Michal Hocko <mhocko@suse.com>
> --
> Michal Hocko
> SUSE Labs
>
> --
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
>
On Wed 25-01-23 08:57:48, Suren Baghdasaryan wrote:
> On Wed, Jan 25, 2023 at 1:38 AM 'Michal Hocko' via kernel-team
> <kernel-team@android.com> wrote:
> >
> > On Wed 25-01-23 00:38:49, Suren Baghdasaryan wrote:
> > > Replace indirect modifications to vma->vm_flags with calls to modifier
> > > functions to be able to track flag changes and to keep vma locking
> > > correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
> > > vm_flags modification attempts.
> >
> > Those BUG_ONs scream to much IMHO. KSM is an MM internal code so I
> > gueess we should be willing to trust it.
>
> Yes, but I really want to prevent an indirect misuse since it was not
> easy to find these. If you feel strongly about it I will remove them
> or if you have a better suggestion I'm all for it.
You can avoid that by making flags inaccesible directly, right?
On Wed, Jan 25, 2023 at 9:08 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Wed 25-01-23 08:57:48, Suren Baghdasaryan wrote:
> > On Wed, Jan 25, 2023 at 1:38 AM 'Michal Hocko' via kernel-team
> > <kernel-team@android.com> wrote:
> > >
> > > On Wed 25-01-23 00:38:49, Suren Baghdasaryan wrote:
> > > > Replace indirect modifications to vma->vm_flags with calls to modifier
> > > > functions to be able to track flag changes and to keep vma locking
> > > > correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
> > > > vm_flags modification attempts.
> > >
> > > Those BUG_ONs scream to much IMHO. KSM is an MM internal code so I
> > > gueess we should be willing to trust it.
> >
> > Yes, but I really want to prevent an indirect misuse since it was not
> > easy to find these. If you feel strongly about it I will remove them
> > or if you have a better suggestion I'm all for it.
>
> You can avoid that by making flags inaccesible directly, right?
Ah, you mean Peter's suggestion of using __private? I guess that would
cover it. I'll drop these BUG_ONs in the next version. Thanks!
>
> --
> Michal Hocko
> SUSE Labs
On Wed, Jan 25, 2023 at 12:38:49AM -0800, Suren Baghdasaryan wrote:
> Replace indirect modifications to vma->vm_flags with calls to modifier
> functions to be able to track flag changes and to keep vma locking
> correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
> vm_flags modification attempts.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
> ---
> arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
> arch/s390/mm/gmap.c | 5 ++++-
> mm/khugepaged.c | 2 ++
> mm/ksm.c | 2 ++
> 4 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index 1d67baa5557a..325a7a47d348 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -393,6 +393,7 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
> {
> unsigned long gfn = memslot->base_gfn;
> unsigned long end, start = gfn_to_hva(kvm, gfn);
> + unsigned long vm_flags;
> int ret = 0;
> struct vm_area_struct *vma;
> int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
> @@ -409,12 +410,14 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
> ret = H_STATE;
> break;
> }
> + vm_flags = vma->vm_flags;
> ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> - merge_flag, &vma->vm_flags);
> + merge_flag, &vm_flags);
> if (ret) {
> ret = H_STATE;
> break;
> }
> + reset_vm_flags(vma, vm_flags);
> start = vma->vm_end;
> } while (end > vma->vm_end);
>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 3a695b8a1e3c..d5eb47dcdacb 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2587,14 +2587,17 @@ int gmap_mark_unmergeable(void)
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> + unsigned long vm_flags;
> int ret;
> VMA_ITERATOR(vmi, mm, 0);
>
> for_each_vma(vmi, vma) {
> + vm_flags = vma->vm_flags;
> ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> - MADV_UNMERGEABLE, &vma->vm_flags);
> + MADV_UNMERGEABLE, &vm_flags);
> if (ret)
> return ret;
> + reset_vm_flags(vma, vm_flags);
> }
> mm->def_flags &= ~VM_MERGEABLE;
> return 0;
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 8abc59345bf2..76b24cd0c179 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -354,6 +354,8 @@ struct attribute_group khugepaged_attr_group = {
> int hugepage_madvise(struct vm_area_struct *vma,
> unsigned long *vm_flags, int advice)
> {
> + /* vma->vm_flags can be changed only using modifier functions */
> + BUG_ON(vm_flags == &vma->vm_flags);
> switch (advice) {
> case MADV_HUGEPAGE:
> #ifdef CONFIG_S390
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 04f1c8c2df11..992b2be9f5e6 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -2573,6 +2573,8 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
> struct mm_struct *mm = vma->vm_mm;
> int err;
>
> + /* vma->vm_flags can be changed only using modifier functions */
> + BUG_ON(vm_flags == &vma->vm_flags);
> switch (advice) {
> case MADV_MERGEABLE:
> /*
> --
> 2.39.1
>
>
@@ -393,6 +393,7 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
{
unsigned long gfn = memslot->base_gfn;
unsigned long end, start = gfn_to_hva(kvm, gfn);
+ unsigned long vm_flags;
int ret = 0;
struct vm_area_struct *vma;
int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
@@ -409,12 +410,14 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
ret = H_STATE;
break;
}
+ vm_flags = vma->vm_flags;
ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
- merge_flag, &vma->vm_flags);
+ merge_flag, &vm_flags);
if (ret) {
ret = H_STATE;
break;
}
+ reset_vm_flags(vma, vm_flags);
start = vma->vm_end;
} while (end > vma->vm_end);
@@ -2587,14 +2587,17 @@ int gmap_mark_unmergeable(void)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
+ unsigned long vm_flags;
int ret;
VMA_ITERATOR(vmi, mm, 0);
for_each_vma(vmi, vma) {
+ vm_flags = vma->vm_flags;
ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
- MADV_UNMERGEABLE, &vma->vm_flags);
+ MADV_UNMERGEABLE, &vm_flags);
if (ret)
return ret;
+ reset_vm_flags(vma, vm_flags);
}
mm->def_flags &= ~VM_MERGEABLE;
return 0;
@@ -354,6 +354,8 @@ struct attribute_group khugepaged_attr_group = {
int hugepage_madvise(struct vm_area_struct *vma,
unsigned long *vm_flags, int advice)
{
+ /* vma->vm_flags can be changed only using modifier functions */
+ BUG_ON(vm_flags == &vma->vm_flags);
switch (advice) {
case MADV_HUGEPAGE:
#ifdef CONFIG_S390
@@ -2573,6 +2573,8 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
struct mm_struct *mm = vma->vm_mm;
int err;
+ /* vma->vm_flags can be changed only using modifier functions */
+ BUG_ON(vm_flags == &vma->vm_flags);
switch (advice) {
case MADV_MERGEABLE:
/*