diff mbox series

mm: Remove HARDENED_USERCOPY_FALLBACK

Message ID 20210921061149.1091163-1-steve@sk2.org (mailing list archive)
State New
Headers show
Series mm: Remove HARDENED_USERCOPY_FALLBACK | expand

Commit Message

Stephen Kitt Sept. 21, 2021, 6:11 a.m. UTC 
This has served its purpose and is no longer used. All usercopy
violations appear to have been handled by now, any remaining
instances (or new bugs) will cause copies to be rejected.

This isn't a direct revert of commit 2d891fbc3bb6 ("usercopy: Allow
strict enforcement of whitelists"); since usercopy_fallback is
effectively 0, the fallback handling is removed too.

This also removes the usercopy_fallback module parameter on
slab_common.

Link: https://github.com/KSPP/linux/issues/153
Signed-off-by: Stephen Kitt <steve@sk2.org>
Suggested-by: Kees Cook <keescook@chromium.org>
---
 arch/powerpc/configs/skiroot_defconfig |  1 -
 include/linux/slab.h                   |  2 --
 mm/slab.c                              | 13 -------------
 mm/slab_common.c                       |  8 --------
 mm/slub.c                              | 14 --------------
 security/Kconfig                       | 14 --------------
 6 files changed, 52 deletions(-)


base-commit: 368094df48e680fa51cedb68537408cfa64b788e

Comments

Kees Cook Sept. 21, 2021, 7:01 p.m. UTC | #1 
On Tue, Sep 21, 2021 at 08:11:49AM +0200, Stephen Kitt wrote:
> This has served its purpose and is no longer used. All usercopy
> violations appear to have been handled by now, any remaining
> instances (or new bugs) will cause copies to be rejected.
> 
> This isn't a direct revert of commit 2d891fbc3bb6 ("usercopy: Allow
> strict enforcement of whitelists"); since usercopy_fallback is
> effectively 0, the fallback handling is removed too.
> 
> This also removes the usercopy_fallback module parameter on
> slab_common.
> 
> Link: https://github.com/KSPP/linux/issues/153
> Signed-off-by: Stephen Kitt <steve@sk2.org>
> Suggested-by: Kees Cook <keescook@chromium.org>

Thanks for doing this!

Acked-by: Kees Cook <keescook@chromium.org>
Joel Stanley Sept. 21, 2021, 11:50 p.m. UTC | #2 
On Tue, 21 Sept 2021 at 09:50, Stephen Kitt <steve@sk2.org> wrote:
>
> This has served its purpose and is no longer used. All usercopy
> violations appear to have been handled by now, any remaining
> instances (or new bugs) will cause copies to be rejected.
>
> This isn't a direct revert of commit 2d891fbc3bb6 ("usercopy: Allow
> strict enforcement of whitelists"); since usercopy_fallback is
> effectively 0, the fallback handling is removed too.
>
> This also removes the usercopy_fallback module parameter on
> slab_common.
>
> Link: https://github.com/KSPP/linux/issues/153
> Signed-off-by: Stephen Kitt <steve@sk2.org>
> Suggested-by: Kees Cook <keescook@chromium.org>
> ---
>  arch/powerpc/configs/skiroot_defconfig |  1 -

For the defconfig change:

Reviewed-by: Joel Stanley <joel@jms.id.au>

Cheers,

Joel

>  include/linux/slab.h                   |  2 --
>  mm/slab.c                              | 13 -------------
>  mm/slab_common.c                       |  8 --------
>  mm/slub.c                              | 14 --------------
>  security/Kconfig                       | 14 --------------
>  6 files changed, 52 deletions(-)
>
> diff --git a/arch/powerpc/configs/skiroot_defconfig b/arch/powerpc/configs/skiroot_defconfig
> index b806a5d3a695..c3ba614c973d 100644
> --- a/arch/powerpc/configs/skiroot_defconfig
> +++ b/arch/powerpc/configs/skiroot_defconfig
> @@ -275,7 +275,6 @@ CONFIG_NLS_UTF8=y
>  CONFIG_ENCRYPTED_KEYS=y
>  CONFIG_SECURITY=y
>  CONFIG_HARDENED_USERCOPY=y
> -# CONFIG_HARDENED_USERCOPY_FALLBACK is not set
>  CONFIG_HARDENED_USERCOPY_PAGESPAN=y
>  CONFIG_FORTIFY_SOURCE=y
>  CONFIG_SECURITY_LOCKDOWN_LSM=y
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 0c97d788762c..5b21515afae0 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -142,8 +142,6 @@ struct mem_cgroup;
>  void __init kmem_cache_init(void);
>  bool slab_is_available(void);
>
> -extern bool usercopy_fallback;
> -
>  struct kmem_cache *kmem_cache_create(const char *name, unsigned int size,
>                         unsigned int align, slab_flags_t flags,
>                         void (*ctor)(void *));
> diff --git a/mm/slab.c b/mm/slab.c
> index d0f725637663..4d826394ffcb 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -4207,19 +4207,6 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
>             n <= cachep->useroffset - offset + cachep->usersize)
>                 return;
>
> -       /*
> -        * If the copy is still within the allocated object, produce
> -        * a warning instead of rejecting the copy. This is intended
> -        * to be a temporary method to find any missing usercopy
> -        * whitelists.
> -        */
> -       if (usercopy_fallback &&
> -           offset <= cachep->object_size &&
> -           n <= cachep->object_size - offset) {
> -               usercopy_warn("SLAB object", cachep->name, to_user, offset, n);
> -               return;
> -       }
> -
>         usercopy_abort("SLAB object", cachep->name, to_user, offset, n);
>  }
>  #endif /* CONFIG_HARDENED_USERCOPY */
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index a4a571428c51..925b00c1d4e8 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -37,14 +37,6 @@ LIST_HEAD(slab_caches);
>  DEFINE_MUTEX(slab_mutex);
>  struct kmem_cache *kmem_cache;
>
> -#ifdef CONFIG_HARDENED_USERCOPY
> -bool usercopy_fallback __ro_after_init =
> -               IS_ENABLED(CONFIG_HARDENED_USERCOPY_FALLBACK);
> -module_param(usercopy_fallback, bool, 0400);
> -MODULE_PARM_DESC(usercopy_fallback,
> -               "WARN instead of reject usercopy whitelist violations");
> -#endif
> -
>  static LIST_HEAD(slab_caches_to_rcu_destroy);
>  static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work);
>  static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
> diff --git a/mm/slub.c b/mm/slub.c
> index 3f96e099817a..77f53e76a3c3 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4125,7 +4125,6 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
>  {
>         struct kmem_cache *s;
>         unsigned int offset;
> -       size_t object_size;
>         bool is_kfence = is_kfence_address(ptr);
>
>         ptr = kasan_reset_tag(ptr);
> @@ -4158,19 +4157,6 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
>             n <= s->useroffset - offset + s->usersize)
>                 return;
>
> -       /*
> -        * If the copy is still within the allocated object, produce
> -        * a warning instead of rejecting the copy. This is intended
> -        * to be a temporary method to find any missing usercopy
> -        * whitelists.
> -        */
> -       object_size = slab_ksize(s);
> -       if (usercopy_fallback &&
> -           offset <= object_size && n <= object_size - offset) {
> -               usercopy_warn("SLUB object", s->name, to_user, offset, n);
> -               return;
> -       }
> -
>         usercopy_abort("SLUB object", s->name, to_user, offset, n);
>  }
>  #endif /* CONFIG_HARDENED_USERCOPY */
> diff --git a/security/Kconfig b/security/Kconfig
> index 0ced7fd33e4d..d9698900c9b7 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -163,20 +163,6 @@ config HARDENED_USERCOPY
>           or are part of the kernel text. This kills entire classes
>           of heap overflow exploits and similar kernel memory exposures.
>
> -config HARDENED_USERCOPY_FALLBACK
> -       bool "Allow usercopy whitelist violations to fallback to object size"
> -       depends on HARDENED_USERCOPY
> -       default y
> -       help
> -         This is a temporary option that allows missing usercopy whitelists
> -         to be discovered via a WARN() to the kernel log, instead of
> -         rejecting the copy, falling back to non-whitelisted hardened
> -         usercopy that checks the slab allocation size instead of the
> -         whitelist size. This option will be removed once it seems like
> -         all missing usercopy whitelists have been identified and fixed.
> -         Booting with "slab_common.usercopy_fallback=Y/N" can change
> -         this setting.
> -
>  config HARDENED_USERCOPY_PAGESPAN
>         bool "Refuse to copy allocations that span multiple pages"
>         depends on HARDENED_USERCOPY
>
> base-commit: 368094df48e680fa51cedb68537408cfa64b788e
> --
> 2.30.2
>
David Rientjes Sept. 26, 2021, 8:49 p.m. UTC | #3 
On Tue, 21 Sep 2021, Stephen Kitt wrote:

> This has served its purpose and is no longer used. All usercopy
> violations appear to have been handled by now, any remaining
> instances (or new bugs) will cause copies to be rejected.
> 
> This isn't a direct revert of commit 2d891fbc3bb6 ("usercopy: Allow
> strict enforcement of whitelists"); since usercopy_fallback is
> effectively 0, the fallback handling is removed too.
> 
> This also removes the usercopy_fallback module parameter on
> slab_common.
> 
> Link: https://github.com/KSPP/linux/issues/153
> Signed-off-by: Stephen Kitt <steve@sk2.org>
> Suggested-by: Kees Cook <keescook@chromium.org>

Acked-by: David Rientjes <rientjes@google.com>
diff mbox series

Patch

diff --git a/arch/powerpc/configs/skiroot_defconfig b/arch/powerpc/configs/skiroot_defconfig
index b806a5d3a695..c3ba614c973d 100644
--- a/arch/powerpc/configs/skiroot_defconfig
+++ b/arch/powerpc/configs/skiroot_defconfig
@@ -275,7 +275,6 @@  CONFIG_NLS_UTF8=y
 CONFIG_ENCRYPTED_KEYS=y
 CONFIG_SECURITY=y
 CONFIG_HARDENED_USERCOPY=y
-# CONFIG_HARDENED_USERCOPY_FALLBACK is not set
 CONFIG_HARDENED_USERCOPY_PAGESPAN=y
 CONFIG_FORTIFY_SOURCE=y
 CONFIG_SECURITY_LOCKDOWN_LSM=y
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 0c97d788762c..5b21515afae0 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -142,8 +142,6 @@  struct mem_cgroup;
 void __init kmem_cache_init(void);
 bool slab_is_available(void);
 
-extern bool usercopy_fallback;
-
 struct kmem_cache *kmem_cache_create(const char *name, unsigned int size,
 			unsigned int align, slab_flags_t flags,
 			void (*ctor)(void *));
diff --git a/mm/slab.c b/mm/slab.c
index d0f725637663..4d826394ffcb 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4207,19 +4207,6 @@  void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 	    n <= cachep->useroffset - offset + cachep->usersize)
 		return;
 
-	/*
-	 * If the copy is still within the allocated object, produce
-	 * a warning instead of rejecting the copy. This is intended
-	 * to be a temporary method to find any missing usercopy
-	 * whitelists.
-	 */
-	if (usercopy_fallback &&
-	    offset <= cachep->object_size &&
-	    n <= cachep->object_size - offset) {
-		usercopy_warn("SLAB object", cachep->name, to_user, offset, n);
-		return;
-	}
-
 	usercopy_abort("SLAB object", cachep->name, to_user, offset, n);
 }
 #endif /* CONFIG_HARDENED_USERCOPY */
diff --git a/mm/slab_common.c b/mm/slab_common.c
index a4a571428c51..925b00c1d4e8 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -37,14 +37,6 @@  LIST_HEAD(slab_caches);
 DEFINE_MUTEX(slab_mutex);
 struct kmem_cache *kmem_cache;
 
-#ifdef CONFIG_HARDENED_USERCOPY
-bool usercopy_fallback __ro_after_init =
-		IS_ENABLED(CONFIG_HARDENED_USERCOPY_FALLBACK);
-module_param(usercopy_fallback, bool, 0400);
-MODULE_PARM_DESC(usercopy_fallback,
-		"WARN instead of reject usercopy whitelist violations");
-#endif
-
 static LIST_HEAD(slab_caches_to_rcu_destroy);
 static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work);
 static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
diff --git a/mm/slub.c b/mm/slub.c
index 3f96e099817a..77f53e76a3c3 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4125,7 +4125,6 @@  void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 {
 	struct kmem_cache *s;
 	unsigned int offset;
-	size_t object_size;
 	bool is_kfence = is_kfence_address(ptr);
 
 	ptr = kasan_reset_tag(ptr);
@@ -4158,19 +4157,6 @@  void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 	    n <= s->useroffset - offset + s->usersize)
 		return;
 
-	/*
-	 * If the copy is still within the allocated object, produce
-	 * a warning instead of rejecting the copy. This is intended
-	 * to be a temporary method to find any missing usercopy
-	 * whitelists.
-	 */
-	object_size = slab_ksize(s);
-	if (usercopy_fallback &&
-	    offset <= object_size && n <= object_size - offset) {
-		usercopy_warn("SLUB object", s->name, to_user, offset, n);
-		return;
-	}
-
 	usercopy_abort("SLUB object", s->name, to_user, offset, n);
 }
 #endif /* CONFIG_HARDENED_USERCOPY */
diff --git a/security/Kconfig b/security/Kconfig
index 0ced7fd33e4d..d9698900c9b7 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -163,20 +163,6 @@  config HARDENED_USERCOPY
 	  or are part of the kernel text. This kills entire classes
 	  of heap overflow exploits and similar kernel memory exposures.
 
-config HARDENED_USERCOPY_FALLBACK
-	bool "Allow usercopy whitelist violations to fallback to object size"
-	depends on HARDENED_USERCOPY
-	default y
-	help
-	  This is a temporary option that allows missing usercopy whitelists
-	  to be discovered via a WARN() to the kernel log, instead of
-	  rejecting the copy, falling back to non-whitelisted hardened
-	  usercopy that checks the slab allocation size instead of the
-	  whitelist size. This option will be removed once it seems like
-	  all missing usercopy whitelists have been identified and fixed.
-	  Booting with "slab_common.usercopy_fallback=Y/N" can change
-	  this setting.
-
 config HARDENED_USERCOPY_PAGESPAN
 	bool "Refuse to copy allocations that span multiple pages"
 	depends on HARDENED_USERCOPY