2023-03-23 02:52:59

by Muchun Song

Subject: [PATCH] mm: kfence: fix handling discontiguous page

The struct pages could be discontiguous when the kfence pool is allocated
via alloc_contig_pages() with CONFIG_SPARSEMEM and !CONFIG_SPARSEMEM_VMEMMAP.
So, the iteration should use nth_page().

Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: Muchun Song <[email protected]>
---
mm/kfence/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index d66092dd187c..1065e0568d05 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -556,7 +556,7 @@ static unsigned long kfence_init_pool(void)
* enters __slab_free() slow-path.
*/
for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
- struct slab *slab = page_slab(&pages[i]);
+ struct slab *slab = page_slab(nth_page(pages, i));

if (!i || (i % 2))
continue;
@@ -602,7 +602,7 @@ static unsigned long kfence_init_pool(void)

reset_slab:
for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
- struct slab *slab = page_slab(&pages[i]);
+ struct slab *slab = page_slab(nth_page(pages, i));

if (!i || (i % 2))
continue;
--
2.11.0

2023-03-23 08:30:45

by Marco Elver

Subject: Re: [PATCH] mm: kfence: fix handling discontiguous page

On Thu, 23 Mar 2023 at 03:50, 'Muchun Song' via kasan-dev
<[email protected]> wrote:
>
> The struct pages could be discontiguous when the kfence pool is allocated
> via alloc_contig_pages() with CONFIG_SPARSEMEM and !CONFIG_SPARSEMEM_VMEMMAP.
> So, the iteration should use nth_page().
>
> Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
> Signed-off-by: Muchun Song <[email protected]>

Reviewed-by: Marco Elver <[email protected]>

> ---
> mm/kfence/core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index d66092dd187c..1065e0568d05 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -556,7 +556,7 @@ static unsigned long kfence_init_pool(void)
> * enters __slab_free() slow-path.
> */
> for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
> - struct slab *slab = page_slab(&pages[i]);
> + struct slab *slab = page_slab(nth_page(pages, i));
>
> if (!i || (i % 2))
> continue;
> @@ -602,7 +602,7 @@ static unsigned long kfence_init_pool(void)
>
> reset_slab:
> for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
> - struct slab *slab = page_slab(&pages[i]);
> + struct slab *slab = page_slab(nth_page(pages, i));
>
> if (!i || (i % 2))
> continue;
> --
> 2.11.0
>
> --
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2023-03-23 22:22:51

by Andrew Morton

Subject: Re: [PATCH] mm: kfence: fix handling discontiguous page

On Thu, 23 Mar 2023 10:50:03 +0800 Muchun Song <[email protected]> wrote:

> The struct pages could be discontiguous when the kfence pool is allocated
> via alloc_contig_pages() with CONFIG_SPARSEMEM and !CONFIG_SPARSEMEM_VMEMMAP.
> So, the iteration should use nth_page().

What are the user-visible runtime effects of this flaw?

Thanks.

2023-03-24 02:13:55

by Muchun Song

Subject: Re: [PATCH] mm: kfence: fix handling discontiguous page

> On Mar 24, 2023, at 06:18, Andrew Morton <[email protected]> wrote:
>
> On Thu, 23 Mar 2023 10:50:03 +0800 Muchun Song <[email protected]> wrote:
>
>> The struct pages could be discontiguous when the kfence pool is allocated
>> via alloc_contig_pages() with CONFIG_SPARSEMEM and !CONFIG_SPARSEMEM_VMEMMAP.
>> So, the iteration should use nth_page().
>
> What are the user-visible runtime effects of this flaw?

Set the PG_slab and memcg_data to a arbitrary address (may be not used as a struct
page), so the worst case may corrupt the kernel.

Thanks.

>
> Thanks.

2023-03-24 03:52:27

by Kefeng Wang

Subject: Re: [PATCH] mm: kfence: fix handling discontiguous page

On 2023/3/23 10:50, Muchun Song wrote:
> The struct pages could be discontiguous when the kfence pool is allocated
> via alloc_contig_pages() with CONFIG_SPARSEMEM and !CONFIG_SPARSEMEM_VMEMMAP.
> So, the iteration should use nth_page().
>

Reviewed-by: Kefeng Wang <[email protected]>

> Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
> Signed-off-by: Muchun Song <[email protected]>
> ---
> mm/kfence/core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index d66092dd187c..1065e0568d05 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -556,7 +556,7 @@ static unsigned long kfence_init_pool(void)
> * enters __slab_free() slow-path.
> */
> for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
> - struct slab *slab = page_slab(&pages[i]);
> + struct slab *slab = page_slab(nth_page(pages, i));
>
> if (!i || (i % 2))
> continue;
> @@ -602,7 +602,7 @@ static unsigned long kfence_init_pool(void)
>
> reset_slab:
> for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
> - struct slab *slab = page_slab(&pages[i]);
> + struct slab *slab = page_slab(nth_page(pages, i));
>
> if (!i || (i % 2))
> continue;