2022-08-03 22:06:44

by Peter Xu

Subject: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

These bits should only be valid when the ptes are present. Introducing two
booleans for it and set it to false when !pte_present().

Cc: Konstantin Khlebnikov <[email protected]>
Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries", 2012-05-31)
Signed-off-by: Peter Xu <[email protected]>
---
fs/proc/task_mmu.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 9913f3be9fd2..482f91577f8c 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
struct vm_area_struct *vma = walk->vma;
bool locked = !!(vma->vm_flags & VM_LOCKED);
struct page *page = NULL;
- bool migration = false;
+ bool migration = false, young = false, dirty = false;

if (pte_present(*pte)) {
page = vm_normal_page(vma, addr, *pte);
+ young = pte_young(*pte);
+ dirty = pte_dirty(*pte);
} else if (is_swap_pte(*pte)) {
swp_entry_t swpent = pte_to_swp_entry(*pte);

@@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
if (!page)
return;

- smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
- locked, migration);
+ smaps_account(mss, page, false, young, dirty, locked, migration);
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
--
2.32.0

2022-08-04 09:45:53

by Vlastimil Babka (SUSE)

Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

On 8/4/22 00:03, Peter Xu wrote:
> These bits should only be valid when the ptes are present. Introducing two
> booleans for it and set it to false when !pte_present().
>
> Cc: Konstantin Khlebnikov <[email protected]>
> Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries", 2012-05-31)
> Signed-off-by: Peter Xu <[email protected]>

Acked-by: Vlastimil Babka <[email protected]>

> ---
> fs/proc/task_mmu.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 9913f3be9fd2..482f91577f8c 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> struct vm_area_struct *vma = walk->vma;
> bool locked = !!(vma->vm_flags & VM_LOCKED);
> struct page *page = NULL;
> - bool migration = false;
> + bool migration = false, young = false, dirty = false;
>
> if (pte_present(*pte)) {
> page = vm_normal_page(vma, addr, *pte);
> + young = pte_young(*pte);
> + dirty = pte_dirty(*pte);
> } else if (is_swap_pte(*pte)) {
> swp_entry_t swpent = pte_to_swp_entry(*pte);
>
> @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> if (!page)
> return;
>
> - smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> - locked, migration);
> + smaps_account(mss, page, false, young, dirty, locked, migration);
> }
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE

2022-08-04 11:17:56

by David Hildenbrand

Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

On 04.08.22 00:03, Peter Xu wrote:
> These bits should only be valid when the ptes are present. Introducing two
> booleans for it and set it to false when !pte_present().
>
> Cc: Konstantin Khlebnikov <[email protected]>
> Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries", 2012-05-31)
> Signed-off-by: Peter Xu <[email protected]>
> ---
> fs/proc/task_mmu.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 9913f3be9fd2..482f91577f8c 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> struct vm_area_struct *vma = walk->vma;
> bool locked = !!(vma->vm_flags & VM_LOCKED);
> struct page *page = NULL;
> - bool migration = false;
> + bool migration = false, young = false, dirty = false;
>
> if (pte_present(*pte)) {
> page = vm_normal_page(vma, addr, *pte);
> + young = pte_young(*pte);
> + dirty = pte_dirty(*pte);
> } else if (is_swap_pte(*pte)) {
> swp_entry_t swpent = pte_to_swp_entry(*pte);
>
> @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> if (!page)
> return;
>
> - smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> - locked, migration);
> + smaps_account(mss, page, false, young, dirty, locked, migration);
> }
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE

Reviewed-by: David Hildenbrand <[email protected]>

--
Thanks,

David / dhildenb

2022-08-04 18:25:55

by Yang Shi

Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

On Wed, Aug 3, 2022 at 3:03 PM Peter Xu <[email protected]> wrote:
>
> These bits should only be valid when the ptes are present. Introducing two
> booleans for it and set it to false when !pte_present().
>
> Cc: Konstantin Khlebnikov <[email protected]>
> Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries", 2012-05-31)
> Signed-off-by: Peter Xu <[email protected]>

Reviewed-by: Yang Shi <[email protected]>

> ---
> fs/proc/task_mmu.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 9913f3be9fd2..482f91577f8c 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> struct vm_area_struct *vma = walk->vma;
> bool locked = !!(vma->vm_flags & VM_LOCKED);
> struct page *page = NULL;
> - bool migration = false;
> + bool migration = false, young = false, dirty = false;
>
> if (pte_present(*pte)) {
> page = vm_normal_page(vma, addr, *pte);
> + young = pte_young(*pte);
> + dirty = pte_dirty(*pte);
> } else if (is_swap_pte(*pte)) {
> swp_entry_t swpent = pte_to_swp_entry(*pte);
>
> @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> if (!page)
> return;
>
> - smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> - locked, migration);
> + smaps_account(mss, page, false, young, dirty, locked, migration);
> }
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> --
> 2.32.0
>

2022-08-04 22:46:42

by Andrew Morton

Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

On Wed, 3 Aug 2022 18:03:29 -0400 Peter Xu <[email protected]> wrote:

> These bits should only be valid when the ptes are present. Introducing two
> booleans for it and set it to false when !pte_present().

Please (always) describe the user visible runtime effects of the bug
which is being fixed?


> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> struct vm_area_struct *vma = walk->vma;
> bool locked = !!(vma->vm_flags & VM_LOCKED);
> struct page *page = NULL;
> - bool migration = false;
> + bool migration = false, young = false, dirty = false;
>
> if (pte_present(*pte)) {
> page = vm_normal_page(vma, addr, *pte);
> + young = pte_young(*pte);
> + dirty = pte_dirty(*pte);
> } else if (is_swap_pte(*pte)) {
> swp_entry_t swpent = pte_to_swp_entry(*pte);
>
> @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> if (!page)
> return;
>
> - smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> - locked, migration);
> + smaps_account(mss, page, false, young, dirty, locked, migration);
> }
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> --
> 2.32.0

2022-08-05 16:29:31

by Peter Xu

Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

On Thu, Aug 04, 2022 at 03:40:50PM -0700, Andrew Morton wrote:
> On Wed, 3 Aug 2022 18:03:29 -0400 Peter Xu <[email protected]> wrote:
>
> > These bits should only be valid when the ptes are present. Introducing two
> > booleans for it and set it to false when !pte_present().
>
> Please (always) describe the user visible runtime effects of the bug
> which is being fixed?

Will do in the future.

For this specific one I'll add some more details:

The bug is found during code reading and no real world issue reported,
but logically such an error can cause incorrect readings for either smaps
or smaps_rollup output on quite a few fields.

For example, it could cause over-estimate on values like Shared_Dirty,
Private_Dirty, Referenced; or it could also cause under-estimate on
values like LazyFree, Shared_Clean, Private_Clean.

Meanwhile I think I overlooked the pmd handling which seems to have the
same issue but done in another commit.. Will repost soon.

Thanks,

>
>
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> > struct vm_area_struct *vma = walk->vma;
> > bool locked = !!(vma->vm_flags & VM_LOCKED);
> > struct page *page = NULL;
> > - bool migration = false;
> > + bool migration = false, young = false, dirty = false;
> >
> > if (pte_present(*pte)) {
> > page = vm_normal_page(vma, addr, *pte);
> > + young = pte_young(*pte);
> > + dirty = pte_dirty(*pte);
> > } else if (is_swap_pte(*pte)) {
> > swp_entry_t swpent = pte_to_swp_entry(*pte);
> >
> > @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> > if (!page)
> > return;
> >
> > - smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> > - locked, migration);
> > + smaps_account(mss, page, false, young, dirty, locked, migration);
> > }
> >
> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > --
> > 2.32.0
>

--
Peter Xu