* Re: [PATCH v3] mm/mm_init: Introduce a boot parameter for check_pages
2025-12-01 18:07 [PATCH v3] mm/mm_init: Introduce a boot parameter for check_pages Joshua Hahn
@ 2025-12-02 10:59 ` Vlastimil Babka
2025-12-02 11:09 ` Mike Rapoport
2025-12-03 9:01 ` Anshuman Khandual
2 siblings, 0 replies; 4+ messages in thread
From: Vlastimil Babka @ 2025-12-02 10:59 UTC (permalink / raw)
To: Joshua Hahn, Andrew Morton
Cc: SeongJae Park, Jonathan Corbet, Mike Rapoport, linux-doc,
linux-kernel, linux-mm, kernel-team
On 12/1/25 7:07 PM, 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.
>
> Acked-by: SeongJae Park <sj@kernel.org>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Thanks!
> ---
> v2 --> v3:
> - Dropped the second patch. I may pursue it at another time : -)
> - Variable renaming (dropping leading _) and cleaner check in
> mem_debugging_and_hardening_init, as suggested by Mike Rapoport
> 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 | 10 +++++++++-
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6c42061ca20e..acdc7fbdecac 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..fc2a6f1e518f 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
> @@ -2534,7 +2542,7 @@ DEFINE_STATIC_KEY_MAYBE(CONFIG_DEBUG_VM, check_pages_enabled);
> static void __init mem_debugging_and_hardening_init(void)
> {
> bool page_poisoning_requested = false;
> - bool want_check_pages = false;
> + bool want_check_pages = check_pages_enabled_early;
>
> #ifdef CONFIG_PAGE_POISONING
> /*
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v3] mm/mm_init: Introduce a boot parameter for check_pages
2025-12-01 18:07 [PATCH v3] mm/mm_init: Introduce a boot parameter for check_pages Joshua Hahn
2025-12-02 10:59 ` Vlastimil Babka
@ 2025-12-02 11:09 ` Mike Rapoport
2025-12-03 9:01 ` Anshuman Khandual
2 siblings, 0 replies; 4+ messages in thread
From: Mike Rapoport @ 2025-12-02 11:09 UTC (permalink / raw)
To: Andrew Morton, Joshua Hahn
Cc: Mike Rapoport, Vlastimil Babka, SeongJae Park, Jonathan Corbet,
linux-doc, linux-kernel, linux-mm, kernel-team
On Mon, 01 Dec 2025 10:07:38 -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.
>
> [...]
Applied to for-next branch of memblock.git tree, thanks!
[1/1] mm/mm_init: Introduce a boot parameter for check_pages
commit: a29b922955aa2bedde15876707532b982dec183c
tree: https://git.kernel.org/pub/scm/linux/kernel/git/rppt/memblock
branch: for-next
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v3] mm/mm_init: Introduce a boot parameter for check_pages
2025-12-01 18:07 [PATCH v3] mm/mm_init: Introduce a boot parameter for check_pages Joshua Hahn
2025-12-02 10:59 ` Vlastimil Babka
2025-12-02 11:09 ` Mike Rapoport
@ 2025-12-03 9:01 ` Anshuman Khandual
2 siblings, 0 replies; 4+ messages in thread
From: Anshuman Khandual @ 2025-12-03 9:01 UTC (permalink / raw)
To: Joshua Hahn, Andrew Morton
Cc: Vlastimil Babka, SeongJae Park, Jonathan Corbet, Mike Rapoport,
linux-doc, linux-kernel, linux-mm, kernel-team
On 01/12/25 11:37 PM, 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.
>
> Acked-by: SeongJae Park <sj@kernel.org>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> ---
> v2 --> v3:
> - Dropped the second patch. I may pursue it at another time : -)
> - Variable renaming (dropping leading _) and cleaner check in
> mem_debugging_and_hardening_init, as suggested by Mike Rapoport
> 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 | 10 +++++++++-
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6c42061ca20e..acdc7fbdecac 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..fc2a6f1e518f 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
> @@ -2534,7 +2542,7 @@ DEFINE_STATIC_KEY_MAYBE(CONFIG_DEBUG_VM, check_pages_enabled);
> static void __init mem_debugging_and_hardening_init(void)
> {
> bool page_poisoning_requested = false;
> - bool want_check_pages = false;
> + bool want_check_pages = check_pages_enabled_early;
>
> #ifdef CONFIG_PAGE_POISONING
> /*
LGTM.
Also a very nice write up for the commit message explaining
the new kernel parameter rationale comprehensively.
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
^ permalink raw reply [flat|nested] 4+ messages in thread