* Re: [PATCH v2 1/2] mm/mm_init: Introduce a boot parameter for check_pages
2025-11-24 22:54 [PATCH v2 1/2] mm/mm_init: Introduce a boot parameter for check_pages Joshua Hahn
@ 2025-11-25 1:10 ` SeongJae Park
2025-11-25 8:44 ` Michal Hocko
2025-11-25 10:23 ` Mike Rapoport
2 siblings, 0 replies; 5+ messages in thread
From: SeongJae Park @ 2025-11-25 1:10 UTC (permalink / raw)
To: Joshua Hahn
Cc: SeongJae Park, Andrew Morton, Vlastimil Babka, Jonathan Corbet,
Mike Rapoport, linux-doc, linux-kernel, linux-mm, kernel-team
On Mon, 24 Nov 2025 14:54:06 -0800 Joshua Hahn <joshua.hahnjy@gmail.com> wrote:
> Use-after-free and double-free bugs can be very difficult to track down.
> The kernel is good at tracking these and preventing bad pages from being
> used/created through simple checks gated behind "check_pages_enabled".
>
> Currently, the only ways to enable this flag is by building with
> CONFIG_DEBUG_VM, or as a side effect of other checks such as
> init_on_{alloc, free}, page_poisoning, or debug_pagealloc among others.
> These solutions are powerful, but may often be too coarse in balancing
> the performance vs. safety that a user may want, particularly in
> latency-sensitive production environments.
>
> Introduce a new boot parameter "check_pages", which enables page checking
> with no other side effects. It takes kstrbool-able inputs as an argument
> (i.e. 0/1, true/false, on/off, ...). This patch is backwards-compatible;
> setting CONFIG_DEBUG_VM still enables page checking.
>
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Acked-by: SeongJae Park <sj@kernel.org>
Thanks,
SJ
[...]
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH v2 1/2] mm/mm_init: Introduce a boot parameter for check_pages
2025-11-24 22:54 [PATCH v2 1/2] mm/mm_init: Introduce a boot parameter for check_pages Joshua Hahn
2025-11-25 1:10 ` SeongJae Park
@ 2025-11-25 8:44 ` Michal Hocko
2025-11-25 10:23 ` Mike Rapoport
2 siblings, 0 replies; 5+ messages in thread
From: Michal Hocko @ 2025-11-25 8:44 UTC (permalink / raw)
To: Joshua Hahn
Cc: Andrew Morton, Vlastimil Babka, Jonathan Corbet, Mike Rapoport,
linux-doc, linux-kernel, linux-mm, kernel-team
On Mon 24-11-25 14:54:06, Joshua Hahn wrote:
> Use-after-free and double-free bugs can be very difficult to track down.
> The kernel is good at tracking these and preventing bad pages from being
> used/created through simple checks gated behind "check_pages_enabled".
>
> Currently, the only ways to enable this flag is by building with
> CONFIG_DEBUG_VM, or as a side effect of other checks such as
> init_on_{alloc, free}, page_poisoning, or debug_pagealloc among others.
> These solutions are powerful, but may often be too coarse in balancing
> the performance vs. safety that a user may want, particularly in
> latency-sensitive production environments.
>
> Introduce a new boot parameter "check_pages", which enables page checking
> with no other side effects. It takes kstrbool-able inputs as an argument
> (i.e. 0/1, true/false, on/off, ...). This patch is backwards-compatible;
> setting CONFIG_DEBUG_VM still enables page checking.
Arguing with performance without any performance numbers is not really
convincing but the change makes some sense to me even without that.
DEBUG_VM is just everything-in-one-bag thing which is not suitable for
production use and bad_page checks might still be valuable for such a
use.
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> v1 --> v2:
> - Changed check_pages from a build config into a boot config, as suggested
> by Vlastimil.
> - Introduced the second patch, which decouples page checking from
> init_on_page_alloc and init_on_page_free.
> ---
>
> Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++
> mm/mm_init.c | 11 ++++++++++-
> 2 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6c42061ca20e..0ba9561440a7 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -669,6 +669,14 @@
> nokmem -- Disable kernel memory accounting.
> nobpf -- Disable BPF memory accounting.
>
> + check_pages= [MM,EARLY] Enable sanity checking of pages after
> + allocations / before freeing. This adds checks to catch
> + double-frees, use-after-frees, and other sources of
> + page corruption by inspecting page internals (flags,
> + mapcount/refcount, memcg_data, etc.).
> + Format: { "0" | "1" }
> + Default: 0 (1 if CONFIG_DEBUG_VM is set)
> +
> checkreqprot= [SELINUX] Set initial checkreqprot flag value.
> Format: { "0" | "1" }
> See security/selinux/Kconfig help text.
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index c6812b4dbb2e..01d46efc42b4 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -2525,6 +2525,14 @@ early_param("init_on_free", early_init_on_free);
>
> DEFINE_STATIC_KEY_MAYBE(CONFIG_DEBUG_VM, check_pages_enabled);
>
> +static bool _check_pages_enabled_early __initdata;
> +
> +static int __init early_check_pages(char *buf)
> +{
> + return kstrtobool(buf, &_check_pages_enabled_early);
> +}
> +early_param("check_pages", early_check_pages);
> +
> /*
> * Enable static keys related to various memory debugging and hardening options.
> * Some override others, and depend on early params that are evaluated in the
> @@ -2591,7 +2599,8 @@ static void __init mem_debugging_and_hardening_init(void)
> * of struct pages being allocated or freed. With CONFIG_DEBUG_VM it's
> * enabled already.
> */
> - if (!IS_ENABLED(CONFIG_DEBUG_VM) && want_check_pages)
> + if (!IS_ENABLED(CONFIG_DEBUG_VM) && (_check_pages_enabled_early ||
> + want_check_pages))
> static_branch_enable(&check_pages_enabled);
> }
>
> --
> 2.47.3
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH v2 1/2] mm/mm_init: Introduce a boot parameter for check_pages
2025-11-24 22:54 [PATCH v2 1/2] mm/mm_init: Introduce a boot parameter for check_pages Joshua Hahn
2025-11-25 1:10 ` SeongJae Park
2025-11-25 8:44 ` Michal Hocko
@ 2025-11-25 10:23 ` Mike Rapoport
2025-11-25 18:44 ` Joshua Hahn
2 siblings, 1 reply; 5+ messages in thread
From: Mike Rapoport @ 2025-11-25 10:23 UTC (permalink / raw)
To: Joshua Hahn
Cc: Andrew Morton, Vlastimil Babka, Jonathan Corbet, linux-doc,
linux-kernel, linux-mm, kernel-team
On Mon, Nov 24, 2025 at 02:54:06PM -0800, Joshua Hahn wrote:
> Use-after-free and double-free bugs can be very difficult to track down.
> The kernel is good at tracking these and preventing bad pages from being
> used/created through simple checks gated behind "check_pages_enabled".
>
> Currently, the only ways to enable this flag is by building with
> CONFIG_DEBUG_VM, or as a side effect of other checks such as
> init_on_{alloc, free}, page_poisoning, or debug_pagealloc among others.
> These solutions are powerful, but may often be too coarse in balancing
> the performance vs. safety that a user may want, particularly in
> latency-sensitive production environments.
>
> Introduce a new boot parameter "check_pages", which enables page checking
> with no other side effects. It takes kstrbool-able inputs as an argument
> (i.e. 0/1, true/false, on/off, ...). This patch is backwards-compatible;
> setting CONFIG_DEBUG_VM still enables page checking.
>
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> ---
> v1 --> v2:
> - Changed check_pages from a build config into a boot config, as suggested
> by Vlastimil.
> - Introduced the second patch, which decouples page checking from
> init_on_page_alloc and init_on_page_free.
> ---
>
> Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++
> mm/mm_init.c | 11 ++++++++++-
> 2 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6c42061ca20e..0ba9561440a7 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -669,6 +669,14 @@
> nokmem -- Disable kernel memory accounting.
> nobpf -- Disable BPF memory accounting.
>
> + check_pages= [MM,EARLY] Enable sanity checking of pages after
> + allocations / before freeing. This adds checks to catch
> + double-frees, use-after-frees, and other sources of
> + page corruption by inspecting page internals (flags,
> + mapcount/refcount, memcg_data, etc.).
> + Format: { "0" | "1" }
> + Default: 0 (1 if CONFIG_DEBUG_VM is set)
> +
> checkreqprot= [SELINUX] Set initial checkreqprot flag value.
> Format: { "0" | "1" }
> See security/selinux/Kconfig help text.
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index c6812b4dbb2e..01d46efc42b4 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -2525,6 +2525,14 @@ early_param("init_on_free", early_init_on_free);
>
> DEFINE_STATIC_KEY_MAYBE(CONFIG_DEBUG_VM, check_pages_enabled);
>
> +static bool _check_pages_enabled_early __initdata;
No need in the leading underscore.
> +
> +static int __init early_check_pages(char *buf)
> +{
> + return kstrtobool(buf, &_check_pages_enabled_early);
> +}
> +early_param("check_pages", early_check_pages);
> +
> /*
> * Enable static keys related to various memory debugging and hardening options.
> * Some override others, and depend on early params that are evaluated in the
> @@ -2591,7 +2599,8 @@ static void __init mem_debugging_and_hardening_init(void)
> * of struct pages being allocated or freed. With CONFIG_DEBUG_VM it's
> * enabled already.
> */
> - if (!IS_ENABLED(CONFIG_DEBUG_VM) && want_check_pages)
> + if (!IS_ENABLED(CONFIG_DEBUG_VM) && (_check_pages_enabled_early ||
> + want_check_pages))
You can initialize want_check_pages to check_pages_enabled_early, would be
clearer IMO.
> static_branch_enable(&check_pages_enabled);
> }
>
> --
> 2.47.3
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH v2 1/2] mm/mm_init: Introduce a boot parameter for check_pages
2025-11-25 10:23 ` Mike Rapoport
@ 2025-11-25 18:44 ` Joshua Hahn
0 siblings, 0 replies; 5+ messages in thread
From: Joshua Hahn @ 2025-11-25 18:44 UTC (permalink / raw)
To: Mike Rapoport
Cc: Andrew Morton, Vlastimil Babka, Jonathan Corbet, linux-doc,
linux-kernel, linux-mm, kernel-team
On Tue, 25 Nov 2025 12:23:14 +0200 Mike Rapoport <rppt@kernel.org> wrote:
> On Mon, Nov 24, 2025 at 02:54:06PM -0800, Joshua Hahn wrote:
> > Use-after-free and double-free bugs can be very difficult to track down.
> > The kernel is good at tracking these and preventing bad pages from being
> > used/created through simple checks gated behind "check_pages_enabled".
> >
> > Currently, the only ways to enable this flag is by building with
> > CONFIG_DEBUG_VM, or as a side effect of other checks such as
> > init_on_{alloc, free}, page_poisoning, or debug_pagealloc among others.
> > These solutions are powerful, but may often be too coarse in balancing
> > the performance vs. safety that a user may want, particularly in
> > latency-sensitive production environments.
> >
> > Introduce a new boot parameter "check_pages", which enables page checking
> > with no other side effects. It takes kstrbool-able inputs as an argument
> > (i.e. 0/1, true/false, on/off, ...). This patch is backwards-compatible;
> > setting CONFIG_DEBUG_VM still enables page checking.
> >
> > Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
...
Hello Mike, thank you for your review!
> > +static bool _check_pages_enabled_early __initdata;
>
> No need in the leading underscore.
Gotcha, no preference here on my end at all, so I'm happy to drop the leading
underscore. I was just modeling the variable after _init_on_alloc_enabled_early
and _init_on_free_enabled_early, but it seems like those are the only ones
that do have this leading underscore anyways.
> > +
> > +static int __init early_check_pages(char *buf)
> > +{
> > + return kstrtobool(buf, &_check_pages_enabled_early);
> > +}
> > +early_param("check_pages", early_check_pages);
> > +
> > /*
> > * Enable static keys related to various memory debugging and hardening options.
> > * Some override others, and depend on early params that are evaluated in the
> > @@ -2591,7 +2599,8 @@ static void __init mem_debugging_and_hardening_init(void)
> > * of struct pages being allocated or freed. With CONFIG_DEBUG_VM it's
> > * enabled already.
> > */
> > - if (!IS_ENABLED(CONFIG_DEBUG_VM) && want_check_pages)
> > + if (!IS_ENABLED(CONFIG_DEBUG_VM) && (_check_pages_enabled_early ||
> > + want_check_pages))
>
> You can initialize want_check_pages to check_pages_enabled_early, would be
> clearer IMO.
Yup, totally makes sense as well. I'll include this change in v3.
Thank you for all your feedback, I hope you have a great day!
Joshua
^ permalink raw reply [flat|nested] 5+ messages in thread