[PATCHv2 0/2] Sanitization of buddy pages

[PATCHv2 0/2] Sanitization of buddy pages

[Laura Abbott]

Hi,

This is v2 of the series to add sanitization to the buddy allocator.
The standard sanitization blurb:

For those who aren't familiar with this, the goal of sanitization is to reduce
the severity of use after free and uninitialized data bugs. Memory is cleared
on free so any sensitive data is no longer available. Discussion of
sanitization was brough up in a thread about CVEs
(lkml.kernel.org/g/<20160119112812.GA10818@mwanda>)

Changes since v1:
- Squashed the refactor and adding the poisoning together. Having them separate
  didn't seem to give much extra benefit and lead to some churn as well.
- Corrected the order of poison vs. kernel_map in the alloc path
- zeroing can now be enabled with hibernation (enabling zero poisoning turns
  off hibernation)
- Added additional checks for skipping __GFP_ZERO. On SPARSEMEM systems the
  extended page flags are not initialized until after memory is freed to the
  buddy list which prevents the pages from being zeroed on first free via
  poisoning. This does also mean that any residual data that may be left in
  the pages from boot up will not be cleared which is a risk. I'm open to
  suggestions for fixing or it can be future work.
- A few spelling/checkpatch fixes.
- Addressed comments from Dave Hansen and Jianyu Zhan
- This series now depends on the change to allow debug_pagealloc_enabled
  to be used without !CONFIG_DEBUG_PAGEALLOC
  (http://article.gmane.org/gmane.linux.kernel.mm/145208)

Thanks,
Laura

Laura Abbott (2):
  mm/page_poison.c: Enable PAGE_POISONING as a separate option
  mm/page_poisoning.c: Allow for zero poisoning

 Documentation/kernel-parameters.txt |   5 +
 include/linux/mm.h                  |  15 +++
 include/linux/poison.h              |   4 +
 kernel/power/hibernate.c            |  17 ++++
 mm/Kconfig.debug                    |  36 ++++++-
 mm/Makefile                         |   2 +-
 mm/debug-pagealloc.c                | 137 ---------------------------
 mm/page_alloc.c                     |  13 ++-
 mm/page_ext.c                       |  10 +-
 mm/page_poison.c                    | 184 ++++++++++++++++++++++++++++++++++++
 10 files changed, 281 insertions(+), 142 deletions(-)
 delete mode 100644 mm/debug-pagealloc.c
 create mode 100644 mm/page_poison.c

-- 
2.5.0

[kernel-hardening] [PATCHv2 0/2] Sanitization of buddy pages

[Laura Abbott]

Hi,

This is v2 of the series to add sanitization to the buddy allocator.
The standard sanitization blurb:

For those who aren't familiar with this, the goal of sanitization is to reduce
the severity of use after free and uninitialized data bugs. Memory is cleared
on free so any sensitive data is no longer available. Discussion of
sanitization was brough up in a thread about CVEs
(lkml.kernel.org/g/<20160119112812.GA10818@mwanda>)

Changes since v1:
- Squashed the refactor and adding the poisoning together. Having them separate
  didn't seem to give much extra benefit and lead to some churn as well.
- Corrected the order of poison vs. kernel_map in the alloc path
- zeroing can now be enabled with hibernation (enabling zero poisoning turns
  off hibernation)
- Added additional checks for skipping __GFP_ZERO. On SPARSEMEM systems the
  extended page flags are not initialized until after memory is freed to the
  buddy list which prevents the pages from being zeroed on first free via
  poisoning. This does also mean that any residual data that may be left in
  the pages from boot up will not be cleared which is a risk. I'm open to
  suggestions for fixing or it can be future work.
- A few spelling/checkpatch fixes.
- Addressed comments from Dave Hansen and Jianyu Zhan
- This series now depends on the change to allow debug_pagealloc_enabled
  to be used without !CONFIG_DEBUG_PAGEALLOC
  (http://article.gmane.org/gmane.linux.kernel.mm/145208)

Thanks,
Laura

Laura Abbott (2):
  mm/page_poison.c: Enable PAGE_POISONING as a separate option
  mm/page_poisoning.c: Allow for zero poisoning

 Documentation/kernel-parameters.txt |   5 +
 include/linux/mm.h                  |  15 +++
 include/linux/poison.h              |   4 +
 kernel/power/hibernate.c            |  17 ++++
 mm/Kconfig.debug                    |  36 ++++++-
 mm/Makefile                         |   2 +-
 mm/debug-pagealloc.c                | 137 ---------------------------
 mm/page_alloc.c                     |  13 ++-
 mm/page_ext.c                       |  10 +-
 mm/page_poison.c                    | 184 ++++++++++++++++++++++++++++++++++++
 10 files changed, 281 insertions(+), 142 deletions(-)
 delete mode 100644 mm/debug-pagealloc.c
 create mode 100644 mm/page_poison.c

-- 
2.5.0

[PATCHv2 0/2] Sanitization of buddy pages

[Laura Abbott]

Hi,

This is v2 of the series to add sanitization to the buddy allocator.
The standard sanitization blurb:

For those who aren't familiar with this, the goal of sanitization is to reduce
the severity of use after free and uninitialized data bugs. Memory is cleared
on free so any sensitive data is no longer available. Discussion of
sanitization was brough up in a thread about CVEs
(lkml.kernel.org/g/<20160119112812.GA10818@mwanda>)

Changes since v1:
- Squashed the refactor and adding the poisoning together. Having them separate
  didn't seem to give much extra benefit and lead to some churn as well.
- Corrected the order of poison vs. kernel_map in the alloc path
- zeroing can now be enabled with hibernation (enabling zero poisoning turns
  off hibernation)
- Added additional checks for skipping __GFP_ZERO. On SPARSEMEM systems the
  extended page flags are not initialized until after memory is freed to the
  buddy list which prevents the pages from being zeroed on first free via
  poisoning. This does also mean that any residual data that may be left in
  the pages from boot up will not be cleared which is a risk. I'm open to
  suggestions for fixing or it can be future work.
- A few spelling/checkpatch fixes.
- Addressed comments from Dave Hansen and Jianyu Zhan
- This series now depends on the change to allow debug_pagealloc_enabled
  to be used without !CONFIG_DEBUG_PAGEALLOC
  (http://article.gmane.org/gmane.linux.kernel.mm/145208)

Thanks,
Laura

Laura Abbott (2):
  mm/page_poison.c: Enable PAGE_POISONING as a separate option
  mm/page_poisoning.c: Allow for zero poisoning

 Documentation/kernel-parameters.txt |   5 +
 include/linux/mm.h                  |  15 +++
 include/linux/poison.h              |   4 +
 kernel/power/hibernate.c            |  17 ++++
 mm/Kconfig.debug                    |  36 ++++++-
 mm/Makefile                         |   2 +-
 mm/debug-pagealloc.c                | 137 ---------------------------
 mm/page_alloc.c                     |  13 ++-
 mm/page_ext.c                       |  10 +-
 mm/page_poison.c                    | 184 ++++++++++++++++++++++++++++++++++++
 10 files changed, 281 insertions(+), 142 deletions(-)
 delete mode 100644 mm/debug-pagealloc.c
 create mode 100644 mm/page_poison.c

-- 
2.5.0

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[PATCHv2 1/2] mm/page_poison.c: Enable PAGE_POISONING as a separate option

[Laura Abbott]

Page poisoning is currently setup as a feature if architectures don't
have architecture debug page_alloc to allow unmapping of pages. It has
uses apart from that though. Clearing of the pages on free provides
an increase in security as it helps to limit the risk of information
leaks. Allow page poisoning to be enabled as a separate option
independent of any other debug feature. Because of how hiberanation
is implemented, the checks on alloc cannot occur if hibernation is
enabled. This option can also be set on !HIBERNATION as well.

Credit to Grsecurity/PaX team for inspiring this work

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
---
 Documentation/kernel-parameters.txt |   5 ++
 include/linux/mm.h                  |   9 ++
 mm/Kconfig.debug                    |  22 ++++-
 mm/Makefile                         |   2 +-
 mm/debug-pagealloc.c                | 137 ----------------------------
 mm/page_alloc.c                     |   2 +
 mm/page_poison.c                    | 173 ++++++++++++++++++++++++++++++++++++
 7 files changed, 211 insertions(+), 139 deletions(-)
 delete mode 100644 mm/debug-pagealloc.c
 create mode 100644 mm/page_poison.c

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 87d40a7..fdade3d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2716,6 +2716,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			we can turn it on.
 			on: enable the feature
 
+	page_poison=	[KNL] Boot-time parameter changing the state of
+			poisoning on the buddy allocator.
+			off: turn off poisoning
+			on: turn on poisoning
+
 	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
 			timeout > 0: seconds before rebooting
 			timeout = 0: wait forever
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f1cd22f..966bf0e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2174,6 +2174,15 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
 			       unsigned long size, pte_fn_t fn, void *data);
 
 
+#ifdef CONFIG_PAGE_POISONING
+extern bool page_poisoning_enabled(void);
+extern void kernel_poison_pages(struct page *page, int numpages, int enable);
+#else
+static inline bool page_poisoning_enabled(void) { return false; }
+static inline void kernel_poison_pages(struct page *page, int numpages,
+					int enable) { }
+#endif
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 extern bool _debug_pagealloc_enabled;
 extern void __kernel_map_pages(struct page *page, int numpages, int enable);
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 957d3da..25c98ae 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -27,4 +27,24 @@ config DEBUG_PAGEALLOC
 	  a resume because free pages are not saved to the suspend image.
 
 config PAGE_POISONING
-	bool
+	bool "Poison pages after freeing"
+	select PAGE_EXTENSION
+	select PAGE_POISONING_NO_SANITY if HIBERNATION
+	---help---
+	  Fill the pages with poison patterns after free_pages() and verify
+	  the patterns before alloc_pages. The filling of the memory helps
+	  reduce the risk of information leaks from freed data. This does
+	  have a potential performance impact.
+
+	  If unsure, say N
+
+config PAGE_POISONING_NO_SANITY
+	depends on PAGE_POISONING
+	bool "Only poison, don't sanity check"
+	---help---
+	   Skip the sanity checking on alloc, only fill the pages with
+	   poison on free. This reduces some of the overhead of the
+	   poisoning feature.
+
+	   If you are only interested in sanitization, say Y. Otherwise
+	   say N.
diff --git a/mm/Makefile b/mm/Makefile
index 2ed4319..cfdd481d 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -48,7 +48,7 @@ obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
 obj-$(CONFIG_SLOB) += slob.o
 obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
 obj-$(CONFIG_KSM) += ksm.o
-obj-$(CONFIG_PAGE_POISONING) += debug-pagealloc.o
+obj-$(CONFIG_PAGE_POISONING) += page_poison.o
 obj-$(CONFIG_SLAB) += slab.o
 obj-$(CONFIG_SLUB) += slub.o
 obj-$(CONFIG_KMEMCHECK) += kmemcheck.o
diff --git a/mm/debug-pagealloc.c b/mm/debug-pagealloc.c
deleted file mode 100644
index 5bf5906..0000000
--- a/mm/debug-pagealloc.c
+++ /dev/null
@@ -1,137 +0,0 @@
-#include <linux/kernel.h>
-#include <linux/string.h>
-#include <linux/mm.h>
-#include <linux/highmem.h>
-#include <linux/page_ext.h>
-#include <linux/poison.h>
-#include <linux/ratelimit.h>
-
-static bool page_poisoning_enabled __read_mostly;
-
-static bool need_page_poisoning(void)
-{
-	if (!debug_pagealloc_enabled())
-		return false;
-
-	return true;
-}
-
-static void init_page_poisoning(void)
-{
-	if (!debug_pagealloc_enabled())
-		return;
-
-	page_poisoning_enabled = true;
-}
-
-struct page_ext_operations page_poisoning_ops = {
-	.need = need_page_poisoning,
-	.init = init_page_poisoning,
-};
-
-static inline void set_page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static inline void clear_page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static inline bool page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static void poison_page(struct page *page)
-{
-	void *addr = kmap_atomic(page);
-
-	set_page_poison(page);
-	memset(addr, PAGE_POISON, PAGE_SIZE);
-	kunmap_atomic(addr);
-}
-
-static void poison_pages(struct page *page, int n)
-{
-	int i;
-
-	for (i = 0; i < n; i++)
-		poison_page(page + i);
-}
-
-static bool single_bit_flip(unsigned char a, unsigned char b)
-{
-	unsigned char error = a ^ b;
-
-	return error && !(error & (error - 1));
-}
-
-static void check_poison_mem(unsigned char *mem, size_t bytes)
-{
-	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
-	unsigned char *start;
-	unsigned char *end;
-
-	start = memchr_inv(mem, PAGE_POISON, bytes);
-	if (!start)
-		return;
-
-	for (end = mem + bytes - 1; end > start; end--) {
-		if (*end != PAGE_POISON)
-			break;
-	}
-
-	if (!__ratelimit(&ratelimit))
-		return;
-	else if (start == end && single_bit_flip(*start, PAGE_POISON))
-		printk(KERN_ERR "pagealloc: single bit error\n");
-	else
-		printk(KERN_ERR "pagealloc: memory corruption\n");
-
-	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
-			end - start + 1, 1);
-	dump_stack();
-}
-
-static void unpoison_page(struct page *page)
-{
-	void *addr;
-
-	if (!page_poison(page))
-		return;
-
-	addr = kmap_atomic(page);
-	check_poison_mem(addr, PAGE_SIZE);
-	clear_page_poison(page);
-	kunmap_atomic(addr);
-}
-
-static void unpoison_pages(struct page *page, int n)
-{
-	int i;
-
-	for (i = 0; i < n; i++)
-		unpoison_page(page + i);
-}
-
-void __kernel_map_pages(struct page *page, int numpages, int enable)
-{
-	if (!page_poisoning_enabled)
-		return;
-
-	if (enable)
-		unpoison_pages(page, numpages);
-	else
-		poison_pages(page, numpages);
-}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 63358d9..cc4762a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1002,6 +1002,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 					   PAGE_SIZE << order);
 	}
 	arch_free_page(page, order);
+	kernel_poison_pages(page, 1 << order, 0);
 	kernel_map_pages(page, 1 << order, 0);
 
 	return true;
@@ -1397,6 +1398,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 
 	arch_alloc_page(page, order);
 	kernel_map_pages(page, 1 << order, 1);
+	kernel_poison_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
 
 	if (gfp_flags & __GFP_ZERO)
diff --git a/mm/page_poison.c b/mm/page_poison.c
new file mode 100644
index 0000000..89d3bc7
--- /dev/null
+++ b/mm/page_poison.c
@@ -0,0 +1,173 @@
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/highmem.h>
+#include <linux/page_ext.h>
+#include <linux/poison.h>
+#include <linux/ratelimit.h>
+
+static bool __page_poisoning_enabled __read_mostly;
+static bool want_page_poisoning __read_mostly;
+
+static int early_page_poison_param(char *buf)
+{
+	if (!buf)
+		return -EINVAL;
+
+	if (strcmp(buf, "on") == 0)
+		want_page_poisoning = true;
+	else if (strcmp(buf, "off") == 0)
+		want_page_poisoning = false;
+
+	return 0;
+}
+early_param("page_poison", early_page_poison_param);
+
+bool page_poisoning_enabled(void)
+{
+	return __page_poisoning_enabled;
+}
+
+static bool need_page_poisoning(void)
+{
+	return want_page_poisoning;
+}
+
+static void init_page_poisoning(void)
+{
+	/*
+	 * page poisoning is debug page alloc for some arches. If either
+	 * of those options are enabled, enable poisoning
+	 */
+	if (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC)) {
+		if (!want_page_poisoning && !debug_pagealloc_enabled())
+			return;
+	} else {
+		if (!want_page_poisoning)
+			return;
+	}
+
+	__page_poisoning_enabled = true;
+}
+
+struct page_ext_operations page_poisoning_ops = {
+	.need = need_page_poisoning,
+	.init = init_page_poisoning,
+};
+
+static inline void set_page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static inline void clear_page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static inline bool page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static void poison_page(struct page *page)
+{
+	void *addr = kmap_atomic(page);
+
+	set_page_poison(page);
+	memset(addr, PAGE_POISON, PAGE_SIZE);
+	kunmap_atomic(addr);
+}
+
+static void poison_pages(struct page *page, int n)
+{
+	int i;
+
+	for (i = 0; i < n; i++)
+		poison_page(page + i);
+}
+
+static bool single_bit_flip(unsigned char a, unsigned char b)
+{
+	unsigned char error = a ^ b;
+
+	return error && !(error & (error - 1));
+}
+
+static void check_poison_mem(unsigned char *mem, size_t bytes)
+{
+	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
+	unsigned char *start;
+	unsigned char *end;
+
+	if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
+		return;
+
+	start = memchr_inv(mem, PAGE_POISON, bytes);
+	if (!start)
+		return;
+
+	for (end = mem + bytes - 1; end > start; end--) {
+		if (*end != PAGE_POISON)
+			break;
+	}
+
+	if (!__ratelimit(&ratelimit))
+		return;
+	else if (start == end && single_bit_flip(*start, PAGE_POISON))
+		pr_err("pagealloc: single bit error\n");
+	else
+		pr_err("pagealloc: memory corruption\n");
+
+	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
+			end - start + 1, 1);
+	dump_stack();
+}
+
+static void unpoison_page(struct page *page)
+{
+	void *addr;
+
+	if (!page_poison(page))
+		return;
+
+	addr = kmap_atomic(page);
+	check_poison_mem(addr, PAGE_SIZE);
+	clear_page_poison(page);
+	kunmap_atomic(addr);
+}
+
+static void unpoison_pages(struct page *page, int n)
+{
+	int i;
+
+	for (i = 0; i < n; i++)
+		unpoison_page(page + i);
+}
+
+void kernel_poison_pages(struct page *page, int numpages, int enable)
+{
+	if (!page_poisoning_enabled())
+		return;
+
+	if (enable)
+		unpoison_pages(page, numpages);
+	else
+		poison_pages(page, numpages);
+}
+
+#ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
+void __kernel_map_pages(struct page *page, int numpages, int enable)
+{
+	/* This function does nothing, all work is done via poison pages */
+}
+#endif
-- 
2.5.0

[kernel-hardening] [PATCHv2 1/2] mm/page_poison.c: Enable PAGE_POISONING as a separate option

[Laura Abbott]

Page poisoning is currently setup as a feature if architectures don't
have architecture debug page_alloc to allow unmapping of pages. It has
uses apart from that though. Clearing of the pages on free provides
an increase in security as it helps to limit the risk of information
leaks. Allow page poisoning to be enabled as a separate option
independent of any other debug feature. Because of how hiberanation
is implemented, the checks on alloc cannot occur if hibernation is
enabled. This option can also be set on !HIBERNATION as well.

Credit to Grsecurity/PaX team for inspiring this work

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
---
 Documentation/kernel-parameters.txt |   5 ++
 include/linux/mm.h                  |   9 ++
 mm/Kconfig.debug                    |  22 ++++-
 mm/Makefile                         |   2 +-
 mm/debug-pagealloc.c                | 137 ----------------------------
 mm/page_alloc.c                     |   2 +
 mm/page_poison.c                    | 173 ++++++++++++++++++++++++++++++++++++
 7 files changed, 211 insertions(+), 139 deletions(-)
 delete mode 100644 mm/debug-pagealloc.c
 create mode 100644 mm/page_poison.c

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 87d40a7..fdade3d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2716,6 +2716,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			we can turn it on.
 			on: enable the feature
 
+	page_poison=	[KNL] Boot-time parameter changing the state of
+			poisoning on the buddy allocator.
+			off: turn off poisoning
+			on: turn on poisoning
+
 	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
 			timeout > 0: seconds before rebooting
 			timeout = 0: wait forever
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f1cd22f..966bf0e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2174,6 +2174,15 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
 			       unsigned long size, pte_fn_t fn, void *data);
 
 
+#ifdef CONFIG_PAGE_POISONING
+extern bool page_poisoning_enabled(void);
+extern void kernel_poison_pages(struct page *page, int numpages, int enable);
+#else
+static inline bool page_poisoning_enabled(void) { return false; }
+static inline void kernel_poison_pages(struct page *page, int numpages,
+					int enable) { }
+#endif
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 extern bool _debug_pagealloc_enabled;
 extern void __kernel_map_pages(struct page *page, int numpages, int enable);
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 957d3da..25c98ae 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -27,4 +27,24 @@ config DEBUG_PAGEALLOC
 	  a resume because free pages are not saved to the suspend image.
 
 config PAGE_POISONING
-	bool
+	bool "Poison pages after freeing"
+	select PAGE_EXTENSION
+	select PAGE_POISONING_NO_SANITY if HIBERNATION
+	---help---
+	  Fill the pages with poison patterns after free_pages() and verify
+	  the patterns before alloc_pages. The filling of the memory helps
+	  reduce the risk of information leaks from freed data. This does
+	  have a potential performance impact.
+
+	  If unsure, say N
+
+config PAGE_POISONING_NO_SANITY
+	depends on PAGE_POISONING
+	bool "Only poison, don't sanity check"
+	---help---
+	   Skip the sanity checking on alloc, only fill the pages with
+	   poison on free. This reduces some of the overhead of the
+	   poisoning feature.
+
+	   If you are only interested in sanitization, say Y. Otherwise
+	   say N.
diff --git a/mm/Makefile b/mm/Makefile
index 2ed4319..cfdd481d 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -48,7 +48,7 @@ obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
 obj-$(CONFIG_SLOB) += slob.o
 obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
 obj-$(CONFIG_KSM) += ksm.o
-obj-$(CONFIG_PAGE_POISONING) += debug-pagealloc.o
+obj-$(CONFIG_PAGE_POISONING) += page_poison.o
 obj-$(CONFIG_SLAB) += slab.o
 obj-$(CONFIG_SLUB) += slub.o
 obj-$(CONFIG_KMEMCHECK) += kmemcheck.o
diff --git a/mm/debug-pagealloc.c b/mm/debug-pagealloc.c
deleted file mode 100644
index 5bf5906..0000000
--- a/mm/debug-pagealloc.c
+++ /dev/null
@@ -1,137 +0,0 @@
-#include <linux/kernel.h>
-#include <linux/string.h>
-#include <linux/mm.h>
-#include <linux/highmem.h>
-#include <linux/page_ext.h>
-#include <linux/poison.h>
-#include <linux/ratelimit.h>
-
-static bool page_poisoning_enabled __read_mostly;
-
-static bool need_page_poisoning(void)
-{
-	if (!debug_pagealloc_enabled())
-		return false;
-
-	return true;
-}
-
-static void init_page_poisoning(void)
-{
-	if (!debug_pagealloc_enabled())
-		return;
-
-	page_poisoning_enabled = true;
-}
-
-struct page_ext_operations page_poisoning_ops = {
-	.need = need_page_poisoning,
-	.init = init_page_poisoning,
-};
-
-static inline void set_page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static inline void clear_page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static inline bool page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static void poison_page(struct page *page)
-{
-	void *addr = kmap_atomic(page);
-
-	set_page_poison(page);
-	memset(addr, PAGE_POISON, PAGE_SIZE);
-	kunmap_atomic(addr);
-}
-
-static void poison_pages(struct page *page, int n)
-{
-	int i;
-
-	for (i = 0; i < n; i++)
-		poison_page(page + i);
-}
-
-static bool single_bit_flip(unsigned char a, unsigned char b)
-{
-	unsigned char error = a ^ b;
-
-	return error && !(error & (error - 1));
-}
-
-static void check_poison_mem(unsigned char *mem, size_t bytes)
-{
-	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
-	unsigned char *start;
-	unsigned char *end;
-
-	start = memchr_inv(mem, PAGE_POISON, bytes);
-	if (!start)
-		return;
-
-	for (end = mem + bytes - 1; end > start; end--) {
-		if (*end != PAGE_POISON)
-			break;
-	}
-
-	if (!__ratelimit(&ratelimit))
-		return;
-	else if (start == end && single_bit_flip(*start, PAGE_POISON))
-		printk(KERN_ERR "pagealloc: single bit error\n");
-	else
-		printk(KERN_ERR "pagealloc: memory corruption\n");
-
-	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
-			end - start + 1, 1);
-	dump_stack();
-}
-
-static void unpoison_page(struct page *page)
-{
-	void *addr;
-
-	if (!page_poison(page))
-		return;
-
-	addr = kmap_atomic(page);
-	check_poison_mem(addr, PAGE_SIZE);
-	clear_page_poison(page);
-	kunmap_atomic(addr);
-}
-
-static void unpoison_pages(struct page *page, int n)
-{
-	int i;
-
-	for (i = 0; i < n; i++)
-		unpoison_page(page + i);
-}
-
-void __kernel_map_pages(struct page *page, int numpages, int enable)
-{
-	if (!page_poisoning_enabled)
-		return;
-
-	if (enable)
-		unpoison_pages(page, numpages);
-	else
-		poison_pages(page, numpages);
-}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 63358d9..cc4762a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1002,6 +1002,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 					   PAGE_SIZE << order);
 	}
 	arch_free_page(page, order);
+	kernel_poison_pages(page, 1 << order, 0);
 	kernel_map_pages(page, 1 << order, 0);
 
 	return true;
@@ -1397,6 +1398,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 
 	arch_alloc_page(page, order);
 	kernel_map_pages(page, 1 << order, 1);
+	kernel_poison_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
 
 	if (gfp_flags & __GFP_ZERO)
diff --git a/mm/page_poison.c b/mm/page_poison.c
new file mode 100644
index 0000000..89d3bc7
--- /dev/null
+++ b/mm/page_poison.c
@@ -0,0 +1,173 @@
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/highmem.h>
+#include <linux/page_ext.h>
+#include <linux/poison.h>
+#include <linux/ratelimit.h>
+
+static bool __page_poisoning_enabled __read_mostly;
+static bool want_page_poisoning __read_mostly;
+
+static int early_page_poison_param(char *buf)
+{
+	if (!buf)
+		return -EINVAL;
+
+	if (strcmp(buf, "on") == 0)
+		want_page_poisoning = true;
+	else if (strcmp(buf, "off") == 0)
+		want_page_poisoning = false;
+
+	return 0;
+}
+early_param("page_poison", early_page_poison_param);
+
+bool page_poisoning_enabled(void)
+{
+	return __page_poisoning_enabled;
+}
+
+static bool need_page_poisoning(void)
+{
+	return want_page_poisoning;
+}
+
+static void init_page_poisoning(void)
+{
+	/*
+	 * page poisoning is debug page alloc for some arches. If either
+	 * of those options are enabled, enable poisoning
+	 */
+	if (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC)) {
+		if (!want_page_poisoning && !debug_pagealloc_enabled())
+			return;
+	} else {
+		if (!want_page_poisoning)
+			return;
+	}
+
+	__page_poisoning_enabled = true;
+}
+
+struct page_ext_operations page_poisoning_ops = {
+	.need = need_page_poisoning,
+	.init = init_page_poisoning,
+};
+
+static inline void set_page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static inline void clear_page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static inline bool page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static void poison_page(struct page *page)
+{
+	void *addr = kmap_atomic(page);
+
+	set_page_poison(page);
+	memset(addr, PAGE_POISON, PAGE_SIZE);
+	kunmap_atomic(addr);
+}
+
+static void poison_pages(struct page *page, int n)
+{
+	int i;
+
+	for (i = 0; i < n; i++)
+		poison_page(page + i);
+}
+
+static bool single_bit_flip(unsigned char a, unsigned char b)
+{
+	unsigned char error = a ^ b;
+
+	return error && !(error & (error - 1));
+}
+
+static void check_poison_mem(unsigned char *mem, size_t bytes)
+{
+	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
+	unsigned char *start;
+	unsigned char *end;
+
+	if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
+		return;
+
+	start = memchr_inv(mem, PAGE_POISON, bytes);
+	if (!start)
+		return;
+
+	for (end = mem + bytes - 1; end > start; end--) {
+		if (*end != PAGE_POISON)
+			break;
+	}
+
+	if (!__ratelimit(&ratelimit))
+		return;
+	else if (start == end && single_bit_flip(*start, PAGE_POISON))
+		pr_err("pagealloc: single bit error\n");
+	else
+		pr_err("pagealloc: memory corruption\n");
+
+	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
+			end - start + 1, 1);
+	dump_stack();
+}
+
+static void unpoison_page(struct page *page)
+{
+	void *addr;
+
+	if (!page_poison(page))
+		return;
+
+	addr = kmap_atomic(page);
+	check_poison_mem(addr, PAGE_SIZE);
+	clear_page_poison(page);
+	kunmap_atomic(addr);
+}
+
+static void unpoison_pages(struct page *page, int n)
+{
+	int i;
+
+	for (i = 0; i < n; i++)
+		unpoison_page(page + i);
+}
+
+void kernel_poison_pages(struct page *page, int numpages, int enable)
+{
+	if (!page_poisoning_enabled())
+		return;
+
+	if (enable)
+		unpoison_pages(page, numpages);
+	else
+		poison_pages(page, numpages);
+}
+
+#ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
+void __kernel_map_pages(struct page *page, int numpages, int enable)
+{
+	/* This function does nothing, all work is done via poison pages */
+}
+#endif
-- 
2.5.0

[PATCHv2 1/2] mm/page_poison.c: Enable PAGE_POISONING as a separate option

[Laura Abbott]

Page poisoning is currently setup as a feature if architectures don't
have architecture debug page_alloc to allow unmapping of pages. It has
uses apart from that though. Clearing of the pages on free provides
an increase in security as it helps to limit the risk of information
leaks. Allow page poisoning to be enabled as a separate option
independent of any other debug feature. Because of how hiberanation
is implemented, the checks on alloc cannot occur if hibernation is
enabled. This option can also be set on !HIBERNATION as well.

Credit to Grsecurity/PaX team for inspiring this work

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
---
 Documentation/kernel-parameters.txt |   5 ++
 include/linux/mm.h                  |   9 ++
 mm/Kconfig.debug                    |  22 ++++-
 mm/Makefile                         |   2 +-
 mm/debug-pagealloc.c                | 137 ----------------------------
 mm/page_alloc.c                     |   2 +
 mm/page_poison.c                    | 173 ++++++++++++++++++++++++++++++++++++
 7 files changed, 211 insertions(+), 139 deletions(-)
 delete mode 100644 mm/debug-pagealloc.c
 create mode 100644 mm/page_poison.c

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 87d40a7..fdade3d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2716,6 +2716,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			we can turn it on.
 			on: enable the feature
 
+	page_poison=	[KNL] Boot-time parameter changing the state of
+			poisoning on the buddy allocator.
+			off: turn off poisoning
+			on: turn on poisoning
+
 	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
 			timeout > 0: seconds before rebooting
 			timeout = 0: wait forever
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f1cd22f..966bf0e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2174,6 +2174,15 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
 			       unsigned long size, pte_fn_t fn, void *data);
 
 
+#ifdef CONFIG_PAGE_POISONING
+extern bool page_poisoning_enabled(void);
+extern void kernel_poison_pages(struct page *page, int numpages, int enable);
+#else
+static inline bool page_poisoning_enabled(void) { return false; }
+static inline void kernel_poison_pages(struct page *page, int numpages,
+					int enable) { }
+#endif
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 extern bool _debug_pagealloc_enabled;
 extern void __kernel_map_pages(struct page *page, int numpages, int enable);
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 957d3da..25c98ae 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -27,4 +27,24 @@ config DEBUG_PAGEALLOC
 	  a resume because free pages are not saved to the suspend image.
 
 config PAGE_POISONING
-	bool
+	bool "Poison pages after freeing"
+	select PAGE_EXTENSION
+	select PAGE_POISONING_NO_SANITY if HIBERNATION
+	---help---
+	  Fill the pages with poison patterns after free_pages() and verify
+	  the patterns before alloc_pages. The filling of the memory helps
+	  reduce the risk of information leaks from freed data. This does
+	  have a potential performance impact.
+
+	  If unsure, say N
+
+config PAGE_POISONING_NO_SANITY
+	depends on PAGE_POISONING
+	bool "Only poison, don't sanity check"
+	---help---
+	   Skip the sanity checking on alloc, only fill the pages with
+	   poison on free. This reduces some of the overhead of the
+	   poisoning feature.
+
+	   If you are only interested in sanitization, say Y. Otherwise
+	   say N.
diff --git a/mm/Makefile b/mm/Makefile
index 2ed4319..cfdd481d 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -48,7 +48,7 @@ obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
 obj-$(CONFIG_SLOB) += slob.o
 obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
 obj-$(CONFIG_KSM) += ksm.o
-obj-$(CONFIG_PAGE_POISONING) += debug-pagealloc.o
+obj-$(CONFIG_PAGE_POISONING) += page_poison.o
 obj-$(CONFIG_SLAB) += slab.o
 obj-$(CONFIG_SLUB) += slub.o
 obj-$(CONFIG_KMEMCHECK) += kmemcheck.o
diff --git a/mm/debug-pagealloc.c b/mm/debug-pagealloc.c
deleted file mode 100644
index 5bf5906..0000000
--- a/mm/debug-pagealloc.c
+++ /dev/null
@@ -1,137 +0,0 @@
-#include <linux/kernel.h>
-#include <linux/string.h>
-#include <linux/mm.h>
-#include <linux/highmem.h>
-#include <linux/page_ext.h>
-#include <linux/poison.h>
-#include <linux/ratelimit.h>
-
-static bool page_poisoning_enabled __read_mostly;
-
-static bool need_page_poisoning(void)
-{
-	if (!debug_pagealloc_enabled())
-		return false;
-
-	return true;
-}
-
-static void init_page_poisoning(void)
-{
-	if (!debug_pagealloc_enabled())
-		return;
-
-	page_poisoning_enabled = true;
-}
-
-struct page_ext_operations page_poisoning_ops = {
-	.need = need_page_poisoning,
-	.init = init_page_poisoning,
-};
-
-static inline void set_page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static inline void clear_page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static inline bool page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static void poison_page(struct page *page)
-{
-	void *addr = kmap_atomic(page);
-
-	set_page_poison(page);
-	memset(addr, PAGE_POISON, PAGE_SIZE);
-	kunmap_atomic(addr);
-}
-
-static void poison_pages(struct page *page, int n)
-{
-	int i;
-
-	for (i = 0; i < n; i++)
-		poison_page(page + i);
-}
-
-static bool single_bit_flip(unsigned char a, unsigned char b)
-{
-	unsigned char error = a ^ b;
-
-	return error && !(error & (error - 1));
-}
-
-static void check_poison_mem(unsigned char *mem, size_t bytes)
-{
-	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
-	unsigned char *start;
-	unsigned char *end;
-
-	start = memchr_inv(mem, PAGE_POISON, bytes);
-	if (!start)
-		return;
-
-	for (end = mem + bytes - 1; end > start; end--) {
-		if (*end != PAGE_POISON)
-			break;
-	}
-
-	if (!__ratelimit(&ratelimit))
-		return;
-	else if (start == end && single_bit_flip(*start, PAGE_POISON))
-		printk(KERN_ERR "pagealloc: single bit error\n");
-	else
-		printk(KERN_ERR "pagealloc: memory corruption\n");
-
-	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
-			end - start + 1, 1);
-	dump_stack();
-}
-
-static void unpoison_page(struct page *page)
-{
-	void *addr;
-
-	if (!page_poison(page))
-		return;
-
-	addr = kmap_atomic(page);
-	check_poison_mem(addr, PAGE_SIZE);
-	clear_page_poison(page);
-	kunmap_atomic(addr);
-}
-
-static void unpoison_pages(struct page *page, int n)
-{
-	int i;
-
-	for (i = 0; i < n; i++)
-		unpoison_page(page + i);
-}
-
-void __kernel_map_pages(struct page *page, int numpages, int enable)
-{
-	if (!page_poisoning_enabled)
-		return;
-
-	if (enable)
-		unpoison_pages(page, numpages);
-	else
-		poison_pages(page, numpages);
-}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 63358d9..cc4762a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1002,6 +1002,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 					   PAGE_SIZE << order);
 	}
 	arch_free_page(page, order);
+	kernel_poison_pages(page, 1 << order, 0);
 	kernel_map_pages(page, 1 << order, 0);
 
 	return true;
@@ -1397,6 +1398,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 
 	arch_alloc_page(page, order);
 	kernel_map_pages(page, 1 << order, 1);
+	kernel_poison_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
 
 	if (gfp_flags & __GFP_ZERO)
diff --git a/mm/page_poison.c b/mm/page_poison.c
new file mode 100644
index 0000000..89d3bc7
--- /dev/null
+++ b/mm/page_poison.c
@@ -0,0 +1,173 @@
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/highmem.h>
+#include <linux/page_ext.h>
+#include <linux/poison.h>
+#include <linux/ratelimit.h>
+
+static bool __page_poisoning_enabled __read_mostly;
+static bool want_page_poisoning __read_mostly;
+
+static int early_page_poison_param(char *buf)
+{
+	if (!buf)
+		return -EINVAL;
+
+	if (strcmp(buf, "on") == 0)
+		want_page_poisoning = true;
+	else if (strcmp(buf, "off") == 0)
+		want_page_poisoning = false;
+
+	return 0;
+}
+early_param("page_poison", early_page_poison_param);
+
+bool page_poisoning_enabled(void)
+{
+	return __page_poisoning_enabled;
+}
+
+static bool need_page_poisoning(void)
+{
+	return want_page_poisoning;
+}
+
+static void init_page_poisoning(void)
+{
+	/*
+	 * page poisoning is debug page alloc for some arches. If either
+	 * of those options are enabled, enable poisoning
+	 */
+	if (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC)) {
+		if (!want_page_poisoning && !debug_pagealloc_enabled())
+			return;
+	} else {
+		if (!want_page_poisoning)
+			return;
+	}
+
+	__page_poisoning_enabled = true;
+}
+
+struct page_ext_operations page_poisoning_ops = {
+	.need = need_page_poisoning,
+	.init = init_page_poisoning,
+};
+
+static inline void set_page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static inline void clear_page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static inline bool page_poison(struct page *page)
+{
+	struct page_ext *page_ext;
+
+	page_ext = lookup_page_ext(page);
+	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+}
+
+static void poison_page(struct page *page)
+{
+	void *addr = kmap_atomic(page);
+
+	set_page_poison(page);
+	memset(addr, PAGE_POISON, PAGE_SIZE);
+	kunmap_atomic(addr);
+}
+
+static void poison_pages(struct page *page, int n)
+{
+	int i;
+
+	for (i = 0; i < n; i++)
+		poison_page(page + i);
+}
+
+static bool single_bit_flip(unsigned char a, unsigned char b)
+{
+	unsigned char error = a ^ b;
+
+	return error && !(error & (error - 1));
+}
+
+static void check_poison_mem(unsigned char *mem, size_t bytes)
+{
+	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
+	unsigned char *start;
+	unsigned char *end;
+
+	if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
+		return;
+
+	start = memchr_inv(mem, PAGE_POISON, bytes);
+	if (!start)
+		return;
+
+	for (end = mem + bytes - 1; end > start; end--) {
+		if (*end != PAGE_POISON)
+			break;
+	}
+
+	if (!__ratelimit(&ratelimit))
+		return;
+	else if (start == end && single_bit_flip(*start, PAGE_POISON))
+		pr_err("pagealloc: single bit error\n");
+	else
+		pr_err("pagealloc: memory corruption\n");
+
+	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
+			end - start + 1, 1);
+	dump_stack();
+}
+
+static void unpoison_page(struct page *page)
+{
+	void *addr;
+
+	if (!page_poison(page))
+		return;
+
+	addr = kmap_atomic(page);
+	check_poison_mem(addr, PAGE_SIZE);
+	clear_page_poison(page);
+	kunmap_atomic(addr);
+}
+
+static void unpoison_pages(struct page *page, int n)
+{
+	int i;
+
+	for (i = 0; i < n; i++)
+		unpoison_page(page + i);
+}
+
+void kernel_poison_pages(struct page *page, int numpages, int enable)
+{
+	if (!page_poisoning_enabled())
+		return;
+
+	if (enable)
+		unpoison_pages(page, numpages);
+	else
+		poison_pages(page, numpages);
+}
+
+#ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
+void __kernel_map_pages(struct page *page, int numpages, int enable)
+{
+	/* This function does nothing, all work is done via poison pages */
+}
+#endif
-- 
2.5.0

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[PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

By default, page poisoning uses a poison value (0xaa) on free. If this
is changed to 0, the page is not only sanitized but zeroing on alloc
with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
corruption from the poisoning is harder to detect. This feature also
cannot be used with hibernation since pages are not guaranteed to be
zeroed after hibernation.

Credit to Grsecurity/PaX team for inspiring this work

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
---
 include/linux/mm.h       |  2 ++
 include/linux/poison.h   |  4 ++++
 kernel/power/hibernate.c | 17 +++++++++++++++++
 mm/Kconfig.debug         | 14 ++++++++++++++
 mm/page_alloc.c          | 11 ++++++++++-
 mm/page_ext.c            | 10 ++++++++--
 mm/page_poison.c         |  7 +++++--
 7 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 966bf0e..59ce0dc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
 #ifdef CONFIG_PAGE_POISONING
 extern bool page_poisoning_enabled(void);
 extern void kernel_poison_pages(struct page *page, int numpages, int enable);
+extern bool page_is_poisoned(struct page *page);
 #else
 static inline bool page_poisoning_enabled(void) { return false; }
 static inline void kernel_poison_pages(struct page *page, int numpages,
 					int enable) { }
+static inline bool page_is_poisoned(struct page *page) { return false; }
 #endif
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
diff --git a/include/linux/poison.h b/include/linux/poison.h
index 4a27153..51334ed 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -30,7 +30,11 @@
 #define TIMER_ENTRY_STATIC	((void *) 0x300 + POISON_POINTER_DELTA)
 
 /********** mm/debug-pagealloc.c **********/
+#ifdef CONFIG_PAGE_POISONING_ZERO
+#define PAGE_POISON 0x00
+#else
 #define PAGE_POISON 0xaa
+#endif
 
 /********** mm/page_alloc.c ************/
 
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index b7342a2..aa0f26b 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
 	return nohibernate_setup(str);
 }
 
+static int __init page_poison_nohibernate_setup(char *str)
+{
+#ifdef CONFIG_PAGE_POISONING_ZERO
+	/*
+	 * The zeroing option for page poison skips the checks on alloc.
+	 * since hibernation doesn't save free pages there's no way to
+	 * guarantee the pages will still be zeroed.
+	 */
+	if (!strcmp(str, "on")) {
+		pr_info("Disabling hibernation due to page poisoning\n");
+		return nohibernate_setup(str);
+	}
+#endif
+	return 1;
+}
+
 __setup("noresume", noresume_setup);
 __setup("resume_offset=", resume_offset_setup);
 __setup("resume=", resume_setup);
@@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
 __setup("resumedelay=", resumedelay_setup);
 __setup("nohibernate", nohibernate_setup);
 __setup("kaslr", kaslr_nohibernate_setup);
+__setup("page_poison=", page_poison_nohibernate_setup);
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 25c98ae..3d3b954 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
 
 	   If you are only interested in sanitization, say Y. Otherwise
 	   say N.
+
+config PAGE_POISONING_ZERO
+	bool "Use zero for poisoning instead of random data"
+	depends on PAGE_POISONING
+	---help---
+	   Instead of using the existing poison value, fill the pages with
+	   zeros. This makes it harder to detect when errors are occurring
+	   due to sanitization but the zeroing at free means that it is
+	   no longer necessary to write zeros when GFP_ZERO is used on
+	   allocation.
+
+	   Enabling page poisoning with this option will disable hibernation
+
+	   If unsure, say N
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cc4762a..59bd9dc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
 	return 0;
 }
 
+static inline bool free_pages_prezeroed(bool poisoned)
+{
+	return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
+		page_poisoning_enabled() && poisoned;
+}
+
 static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 								int alloc_flags)
 {
 	int i;
+	bool poisoned = true;
 
 	for (i = 0; i < (1 << order); i++) {
 		struct page *p = page + i;
 		if (unlikely(check_new_page(p)))
 			return 1;
+		if (poisoned)
+			poisoned &= page_is_poisoned(p);
 	}
 
 	set_page_private(page, 0);
@@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 	kernel_poison_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
 
-	if (gfp_flags & __GFP_ZERO)
+	if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
 		for (i = 0; i < (1 << order); i++)
 			clear_highpage(page + i);
 
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 292ca7b..2d864e6 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
 	struct page_ext *base;
 
 	base = NODE_DATA(page_to_nid(page))->node_page_ext;
-#ifdef CONFIG_DEBUG_VM
+#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
 	/*
 	 * The sanity checks the page allocator does upon freeing a
 	 * page can reach here before the page_ext arrays are
 	 * allocated when feeding a range of pages to the allocator
 	 * for the first time during bootup or memory hotplug.
+	 *
+	 * This check is also necessary for ensuring page poisoning
+	 * works as expected when enabled
 	 */
 	if (unlikely(!base))
 		return NULL;
@@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
 	struct mem_section *section = __pfn_to_section(pfn);
-#ifdef CONFIG_DEBUG_VM
+#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
 	/*
 	 * The sanity checks the page allocator does upon freeing a
 	 * page can reach here before the page_ext arrays are
 	 * allocated when feeding a range of pages to the allocator
 	 * for the first time during bootup or memory hotplug.
+	 *
+	 * This check is also necessary for ensuring page poisoning
+	 * works as expected when enabled
 	 */
 	if (!section->page_ext)
 		return NULL;
diff --git a/mm/page_poison.c b/mm/page_poison.c
index 89d3bc7..479e7ea 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
 	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
 }
 
-static inline bool page_poison(struct page *page)
+bool page_is_poisoned(struct page *page)
 {
 	struct page_ext *page_ext;
 
 	page_ext = lookup_page_ext(page);
+	if (!page_ext)
+		return false;
+
 	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
 }
 
@@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
 {
 	void *addr;
 
-	if (!page_poison(page))
+	if (!page_is_poisoned(page))
 		return;
 
 	addr = kmap_atomic(page);
-- 
2.5.0

[kernel-hardening] [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

By default, page poisoning uses a poison value (0xaa) on free. If this
is changed to 0, the page is not only sanitized but zeroing on alloc
with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
corruption from the poisoning is harder to detect. This feature also
cannot be used with hibernation since pages are not guaranteed to be
zeroed after hibernation.

Credit to Grsecurity/PaX team for inspiring this work

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
---
 include/linux/mm.h       |  2 ++
 include/linux/poison.h   |  4 ++++
 kernel/power/hibernate.c | 17 +++++++++++++++++
 mm/Kconfig.debug         | 14 ++++++++++++++
 mm/page_alloc.c          | 11 ++++++++++-
 mm/page_ext.c            | 10 ++++++++--
 mm/page_poison.c         |  7 +++++--
 7 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 966bf0e..59ce0dc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
 #ifdef CONFIG_PAGE_POISONING
 extern bool page_poisoning_enabled(void);
 extern void kernel_poison_pages(struct page *page, int numpages, int enable);
+extern bool page_is_poisoned(struct page *page);
 #else
 static inline bool page_poisoning_enabled(void) { return false; }
 static inline void kernel_poison_pages(struct page *page, int numpages,
 					int enable) { }
+static inline bool page_is_poisoned(struct page *page) { return false; }
 #endif
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
diff --git a/include/linux/poison.h b/include/linux/poison.h
index 4a27153..51334ed 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -30,7 +30,11 @@
 #define TIMER_ENTRY_STATIC	((void *) 0x300 + POISON_POINTER_DELTA)
 
 /********** mm/debug-pagealloc.c **********/
+#ifdef CONFIG_PAGE_POISONING_ZERO
+#define PAGE_POISON 0x00
+#else
 #define PAGE_POISON 0xaa
+#endif
 
 /********** mm/page_alloc.c ************/
 
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index b7342a2..aa0f26b 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
 	return nohibernate_setup(str);
 }
 
+static int __init page_poison_nohibernate_setup(char *str)
+{
+#ifdef CONFIG_PAGE_POISONING_ZERO
+	/*
+	 * The zeroing option for page poison skips the checks on alloc.
+	 * since hibernation doesn't save free pages there's no way to
+	 * guarantee the pages will still be zeroed.
+	 */
+	if (!strcmp(str, "on")) {
+		pr_info("Disabling hibernation due to page poisoning\n");
+		return nohibernate_setup(str);
+	}
+#endif
+	return 1;
+}
+
 __setup("noresume", noresume_setup);
 __setup("resume_offset=", resume_offset_setup);
 __setup("resume=", resume_setup);
@@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
 __setup("resumedelay=", resumedelay_setup);
 __setup("nohibernate", nohibernate_setup);
 __setup("kaslr", kaslr_nohibernate_setup);
+__setup("page_poison=", page_poison_nohibernate_setup);
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 25c98ae..3d3b954 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
 
 	   If you are only interested in sanitization, say Y. Otherwise
 	   say N.
+
+config PAGE_POISONING_ZERO
+	bool "Use zero for poisoning instead of random data"
+	depends on PAGE_POISONING
+	---help---
+	   Instead of using the existing poison value, fill the pages with
+	   zeros. This makes it harder to detect when errors are occurring
+	   due to sanitization but the zeroing at free means that it is
+	   no longer necessary to write zeros when GFP_ZERO is used on
+	   allocation.
+
+	   Enabling page poisoning with this option will disable hibernation
+
+	   If unsure, say N
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cc4762a..59bd9dc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
 	return 0;
 }
 
+static inline bool free_pages_prezeroed(bool poisoned)
+{
+	return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
+		page_poisoning_enabled() && poisoned;
+}
+
 static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 								int alloc_flags)
 {
 	int i;
+	bool poisoned = true;
 
 	for (i = 0; i < (1 << order); i++) {
 		struct page *p = page + i;
 		if (unlikely(check_new_page(p)))
 			return 1;
+		if (poisoned)
+			poisoned &= page_is_poisoned(p);
 	}
 
 	set_page_private(page, 0);
@@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 	kernel_poison_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
 
-	if (gfp_flags & __GFP_ZERO)
+	if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
 		for (i = 0; i < (1 << order); i++)
 			clear_highpage(page + i);
 
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 292ca7b..2d864e6 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
 	struct page_ext *base;
 
 	base = NODE_DATA(page_to_nid(page))->node_page_ext;
-#ifdef CONFIG_DEBUG_VM
+#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
 	/*
 	 * The sanity checks the page allocator does upon freeing a
 	 * page can reach here before the page_ext arrays are
 	 * allocated when feeding a range of pages to the allocator
 	 * for the first time during bootup or memory hotplug.
+	 *
+	 * This check is also necessary for ensuring page poisoning
+	 * works as expected when enabled
 	 */
 	if (unlikely(!base))
 		return NULL;
@@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
 	struct mem_section *section = __pfn_to_section(pfn);
-#ifdef CONFIG_DEBUG_VM
+#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
 	/*
 	 * The sanity checks the page allocator does upon freeing a
 	 * page can reach here before the page_ext arrays are
 	 * allocated when feeding a range of pages to the allocator
 	 * for the first time during bootup or memory hotplug.
+	 *
+	 * This check is also necessary for ensuring page poisoning
+	 * works as expected when enabled
 	 */
 	if (!section->page_ext)
 		return NULL;
diff --git a/mm/page_poison.c b/mm/page_poison.c
index 89d3bc7..479e7ea 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
 	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
 }
 
-static inline bool page_poison(struct page *page)
+bool page_is_poisoned(struct page *page)
 {
 	struct page_ext *page_ext;
 
 	page_ext = lookup_page_ext(page);
+	if (!page_ext)
+		return false;
+
 	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
 }
 
@@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
 {
 	void *addr;
 
-	if (!page_poison(page))
+	if (!page_is_poisoned(page))
 		return;
 
 	addr = kmap_atomic(page);
-- 
2.5.0

[PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

By default, page poisoning uses a poison value (0xaa) on free. If this
is changed to 0, the page is not only sanitized but zeroing on alloc
with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
corruption from the poisoning is harder to detect. This feature also
cannot be used with hibernation since pages are not guaranteed to be
zeroed after hibernation.

Credit to Grsecurity/PaX team for inspiring this work

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
---
 include/linux/mm.h       |  2 ++
 include/linux/poison.h   |  4 ++++
 kernel/power/hibernate.c | 17 +++++++++++++++++
 mm/Kconfig.debug         | 14 ++++++++++++++
 mm/page_alloc.c          | 11 ++++++++++-
 mm/page_ext.c            | 10 ++++++++--
 mm/page_poison.c         |  7 +++++--
 7 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 966bf0e..59ce0dc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
 #ifdef CONFIG_PAGE_POISONING
 extern bool page_poisoning_enabled(void);
 extern void kernel_poison_pages(struct page *page, int numpages, int enable);
+extern bool page_is_poisoned(struct page *page);
 #else
 static inline bool page_poisoning_enabled(void) { return false; }
 static inline void kernel_poison_pages(struct page *page, int numpages,
 					int enable) { }
+static inline bool page_is_poisoned(struct page *page) { return false; }
 #endif
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
diff --git a/include/linux/poison.h b/include/linux/poison.h
index 4a27153..51334ed 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -30,7 +30,11 @@
 #define TIMER_ENTRY_STATIC	((void *) 0x300 + POISON_POINTER_DELTA)
 
 /********** mm/debug-pagealloc.c **********/
+#ifdef CONFIG_PAGE_POISONING_ZERO
+#define PAGE_POISON 0x00
+#else
 #define PAGE_POISON 0xaa
+#endif
 
 /********** mm/page_alloc.c ************/
 
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index b7342a2..aa0f26b 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
 	return nohibernate_setup(str);
 }
 
+static int __init page_poison_nohibernate_setup(char *str)
+{
+#ifdef CONFIG_PAGE_POISONING_ZERO
+	/*
+	 * The zeroing option for page poison skips the checks on alloc.
+	 * since hibernation doesn't save free pages there's no way to
+	 * guarantee the pages will still be zeroed.
+	 */
+	if (!strcmp(str, "on")) {
+		pr_info("Disabling hibernation due to page poisoning\n");
+		return nohibernate_setup(str);
+	}
+#endif
+	return 1;
+}
+
 __setup("noresume", noresume_setup);
 __setup("resume_offset=", resume_offset_setup);
 __setup("resume=", resume_setup);
@@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
 __setup("resumedelay=", resumedelay_setup);
 __setup("nohibernate", nohibernate_setup);
 __setup("kaslr", kaslr_nohibernate_setup);
+__setup("page_poison=", page_poison_nohibernate_setup);
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 25c98ae..3d3b954 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
 
 	   If you are only interested in sanitization, say Y. Otherwise
 	   say N.
+
+config PAGE_POISONING_ZERO
+	bool "Use zero for poisoning instead of random data"
+	depends on PAGE_POISONING
+	---help---
+	   Instead of using the existing poison value, fill the pages with
+	   zeros. This makes it harder to detect when errors are occurring
+	   due to sanitization but the zeroing at free means that it is
+	   no longer necessary to write zeros when GFP_ZERO is used on
+	   allocation.
+
+	   Enabling page poisoning with this option will disable hibernation
+
+	   If unsure, say N
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cc4762a..59bd9dc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
 	return 0;
 }
 
+static inline bool free_pages_prezeroed(bool poisoned)
+{
+	return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
+		page_poisoning_enabled() && poisoned;
+}
+
 static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 								int alloc_flags)
 {
 	int i;
+	bool poisoned = true;
 
 	for (i = 0; i < (1 << order); i++) {
 		struct page *p = page + i;
 		if (unlikely(check_new_page(p)))
 			return 1;
+		if (poisoned)
+			poisoned &= page_is_poisoned(p);
 	}
 
 	set_page_private(page, 0);
@@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 	kernel_poison_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
 
-	if (gfp_flags & __GFP_ZERO)
+	if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
 		for (i = 0; i < (1 << order); i++)
 			clear_highpage(page + i);
 
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 292ca7b..2d864e6 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
 	struct page_ext *base;
 
 	base = NODE_DATA(page_to_nid(page))->node_page_ext;
-#ifdef CONFIG_DEBUG_VM
+#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
 	/*
 	 * The sanity checks the page allocator does upon freeing a
 	 * page can reach here before the page_ext arrays are
 	 * allocated when feeding a range of pages to the allocator
 	 * for the first time during bootup or memory hotplug.
+	 *
+	 * This check is also necessary for ensuring page poisoning
+	 * works as expected when enabled
 	 */
 	if (unlikely(!base))
 		return NULL;
@@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
 	struct mem_section *section = __pfn_to_section(pfn);
-#ifdef CONFIG_DEBUG_VM
+#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
 	/*
 	 * The sanity checks the page allocator does upon freeing a
 	 * page can reach here before the page_ext arrays are
 	 * allocated when feeding a range of pages to the allocator
 	 * for the first time during bootup or memory hotplug.
+	 *
+	 * This check is also necessary for ensuring page poisoning
+	 * works as expected when enabled
 	 */
 	if (!section->page_ext)
 		return NULL;
diff --git a/mm/page_poison.c b/mm/page_poison.c
index 89d3bc7..479e7ea 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
 	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
 }
 
-static inline bool page_poison(struct page *page)
+bool page_is_poisoned(struct page *page)
 {
 	struct page_ext *page_ext;
 
 	page_ext = lookup_page_ext(page);
+	if (!page_ext)
+		return false;
+
 	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
 }
 
@@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
 {
 	void *addr;
 
-	if (!page_poison(page))
+	if (!page_is_poisoned(page))
 		return;
 
 	addr = kmap_atomic(page);
-- 
2.5.0

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Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Rafael J. Wysocki]

On Thursday, January 28, 2016 06:38:19 PM Laura Abbott wrote:
> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.
> 
> Credit to Grsecurity/PaX team for inspiring this work
> 
> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>

The hibernation disabling part is fine by me.

Please feel free to add an ACK from me to this if that helps.

Thanks,
Rafael

[kernel-hardening] Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Rafael J. Wysocki]

On Thursday, January 28, 2016 06:38:19 PM Laura Abbott wrote:
> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.
> 
> Credit to Grsecurity/PaX team for inspiring this work
> 
> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>

The hibernation disabling part is fine by me.

Please feel free to add an ACK from me to this if that helps.

Thanks,
Rafael

Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Rafael J. Wysocki]

On Thursday, January 28, 2016 06:38:19 PM Laura Abbott wrote:
> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.
> 
> Credit to Grsecurity/PaX team for inspiring this work
> 
> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>

The hibernation disabling part is fine by me.

Please feel free to add an ACK from me to this if that helps.

Thanks,
Rafael

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
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Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Kees Cook]

On Thu, Jan 28, 2016 at 6:38 PM, Laura Abbott <labbott@fedoraproject.org> wrote:
> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.
>
> Credit to Grsecurity/PaX team for inspiring this work
>
> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
> ---
>  include/linux/mm.h       |  2 ++
>  include/linux/poison.h   |  4 ++++
>  kernel/power/hibernate.c | 17 +++++++++++++++++
>  mm/Kconfig.debug         | 14 ++++++++++++++
>  mm/page_alloc.c          | 11 ++++++++++-
>  mm/page_ext.c            | 10 ++++++++--
>  mm/page_poison.c         |  7 +++++--
>  7 files changed, 60 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 966bf0e..59ce0dc 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>  #ifdef CONFIG_PAGE_POISONING
>  extern bool page_poisoning_enabled(void);
>  extern void kernel_poison_pages(struct page *page, int numpages, int enable);
> +extern bool page_is_poisoned(struct page *page);
>  #else
>  static inline bool page_poisoning_enabled(void) { return false; }
>  static inline void kernel_poison_pages(struct page *page, int numpages,
>                                         int enable) { }
> +static inline bool page_is_poisoned(struct page *page) { return false; }
>  #endif
>
>  #ifdef CONFIG_DEBUG_PAGEALLOC
> diff --git a/include/linux/poison.h b/include/linux/poison.h
> index 4a27153..51334ed 100644
> --- a/include/linux/poison.h
> +++ b/include/linux/poison.h
> @@ -30,7 +30,11 @@
>  #define TIMER_ENTRY_STATIC     ((void *) 0x300 + POISON_POINTER_DELTA)
>
>  /********** mm/debug-pagealloc.c **********/
> +#ifdef CONFIG_PAGE_POISONING_ZERO
> +#define PAGE_POISON 0x00
> +#else
>  #define PAGE_POISON 0xaa
> +#endif
>
>  /********** mm/page_alloc.c ************/
>
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index b7342a2..aa0f26b 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
>         return nohibernate_setup(str);
>  }
>
> +static int __init page_poison_nohibernate_setup(char *str)
> +{
> +#ifdef CONFIG_PAGE_POISONING_ZERO
> +       /*
> +        * The zeroing option for page poison skips the checks on alloc.
> +        * since hibernation doesn't save free pages there's no way to
> +        * guarantee the pages will still be zeroed.
> +        */
> +       if (!strcmp(str, "on")) {
> +               pr_info("Disabling hibernation due to page poisoning\n");
> +               return nohibernate_setup(str);
> +       }
> +#endif
> +       return 1;
> +}
> +
>  __setup("noresume", noresume_setup);
>  __setup("resume_offset=", resume_offset_setup);
>  __setup("resume=", resume_setup);
> @@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
>  __setup("resumedelay=", resumedelay_setup);
>  __setup("nohibernate", nohibernate_setup);
>  __setup("kaslr", kaslr_nohibernate_setup);
> +__setup("page_poison=", page_poison_nohibernate_setup);
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 25c98ae..3d3b954 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
>
>            If you are only interested in sanitization, say Y. Otherwise
>            say N.
> +
> +config PAGE_POISONING_ZERO
> +       bool "Use zero for poisoning instead of random data"
> +       depends on PAGE_POISONING
> +       ---help---
> +          Instead of using the existing poison value, fill the pages with
> +          zeros. This makes it harder to detect when errors are occurring
> +          due to sanitization but the zeroing at free means that it is
> +          no longer necessary to write zeros when GFP_ZERO is used on
> +          allocation.

May be worth noting the security benefit in this help text.

> +
> +          Enabling page poisoning with this option will disable hibernation

This isn't obvious to me. It looks like you need to both use
CONFIG_PAGE_POISOING_ZERO and put "page_poison=on" on the command line
to enable it?

-Kees

> +
> +          If unsure, say N
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cc4762a..59bd9dc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
>         return 0;
>  }
>
> +static inline bool free_pages_prezeroed(bool poisoned)
> +{
> +       return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
> +               page_poisoning_enabled() && poisoned;
> +}
> +
>  static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>                                                                 int alloc_flags)
>  {
>         int i;
> +       bool poisoned = true;
>
>         for (i = 0; i < (1 << order); i++) {
>                 struct page *p = page + i;
>                 if (unlikely(check_new_page(p)))
>                         return 1;
> +               if (poisoned)
> +                       poisoned &= page_is_poisoned(p);
>         }
>
>         set_page_private(page, 0);
> @@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>         kernel_poison_pages(page, 1 << order, 1);
>         kasan_alloc_pages(page, order);
>
> -       if (gfp_flags & __GFP_ZERO)
> +       if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
>                 for (i = 0; i < (1 << order); i++)
>                         clear_highpage(page + i);
>
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 292ca7b..2d864e6 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>         struct page_ext *base;
>
>         base = NODE_DATA(page_to_nid(page))->node_page_ext;
> -#ifdef CONFIG_DEBUG_VM
> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>         /*
>          * The sanity checks the page allocator does upon freeing a
>          * page can reach here before the page_ext arrays are
>          * allocated when feeding a range of pages to the allocator
>          * for the first time during bootup or memory hotplug.
> +        *
> +        * This check is also necessary for ensuring page poisoning
> +        * works as expected when enabled
>          */
>         if (unlikely(!base))
>                 return NULL;
> @@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>  {
>         unsigned long pfn = page_to_pfn(page);
>         struct mem_section *section = __pfn_to_section(pfn);
> -#ifdef CONFIG_DEBUG_VM
> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>         /*
>          * The sanity checks the page allocator does upon freeing a
>          * page can reach here before the page_ext arrays are
>          * allocated when feeding a range of pages to the allocator
>          * for the first time during bootup or memory hotplug.
> +        *
> +        * This check is also necessary for ensuring page poisoning
> +        * works as expected when enabled
>          */
>         if (!section->page_ext)
>                 return NULL;
> diff --git a/mm/page_poison.c b/mm/page_poison.c
> index 89d3bc7..479e7ea 100644
> --- a/mm/page_poison.c
> +++ b/mm/page_poison.c
> @@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
>         __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>  }
>
> -static inline bool page_poison(struct page *page)
> +bool page_is_poisoned(struct page *page)
>  {
>         struct page_ext *page_ext;
>
>         page_ext = lookup_page_ext(page);
> +       if (!page_ext)
> +               return false;
> +
>         return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>  }
>
> @@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
>  {
>         void *addr;
>
> -       if (!page_poison(page))
> +       if (!page_is_poisoned(page))
>                 return;
>
>         addr = kmap_atomic(page);
> --
> 2.5.0
>



-- 
Kees Cook
Chrome OS & Brillo Security

[kernel-hardening] Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Kees Cook]

On Thu, Jan 28, 2016 at 6:38 PM, Laura Abbott <labbott@fedoraproject.org> wrote:
> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.
>
> Credit to Grsecurity/PaX team for inspiring this work
>
> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
> ---
>  include/linux/mm.h       |  2 ++
>  include/linux/poison.h   |  4 ++++
>  kernel/power/hibernate.c | 17 +++++++++++++++++
>  mm/Kconfig.debug         | 14 ++++++++++++++
>  mm/page_alloc.c          | 11 ++++++++++-
>  mm/page_ext.c            | 10 ++++++++--
>  mm/page_poison.c         |  7 +++++--
>  7 files changed, 60 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 966bf0e..59ce0dc 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>  #ifdef CONFIG_PAGE_POISONING
>  extern bool page_poisoning_enabled(void);
>  extern void kernel_poison_pages(struct page *page, int numpages, int enable);
> +extern bool page_is_poisoned(struct page *page);
>  #else
>  static inline bool page_poisoning_enabled(void) { return false; }
>  static inline void kernel_poison_pages(struct page *page, int numpages,
>                                         int enable) { }
> +static inline bool page_is_poisoned(struct page *page) { return false; }
>  #endif
>
>  #ifdef CONFIG_DEBUG_PAGEALLOC
> diff --git a/include/linux/poison.h b/include/linux/poison.h
> index 4a27153..51334ed 100644
> --- a/include/linux/poison.h
> +++ b/include/linux/poison.h
> @@ -30,7 +30,11 @@
>  #define TIMER_ENTRY_STATIC     ((void *) 0x300 + POISON_POINTER_DELTA)
>
>  /********** mm/debug-pagealloc.c **********/
> +#ifdef CONFIG_PAGE_POISONING_ZERO
> +#define PAGE_POISON 0x00
> +#else
>  #define PAGE_POISON 0xaa
> +#endif
>
>  /********** mm/page_alloc.c ************/
>
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index b7342a2..aa0f26b 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
>         return nohibernate_setup(str);
>  }
>
> +static int __init page_poison_nohibernate_setup(char *str)
> +{
> +#ifdef CONFIG_PAGE_POISONING_ZERO
> +       /*
> +        * The zeroing option for page poison skips the checks on alloc.
> +        * since hibernation doesn't save free pages there's no way to
> +        * guarantee the pages will still be zeroed.
> +        */
> +       if (!strcmp(str, "on")) {
> +               pr_info("Disabling hibernation due to page poisoning\n");
> +               return nohibernate_setup(str);
> +       }
> +#endif
> +       return 1;
> +}
> +
>  __setup("noresume", noresume_setup);
>  __setup("resume_offset=", resume_offset_setup);
>  __setup("resume=", resume_setup);
> @@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
>  __setup("resumedelay=", resumedelay_setup);
>  __setup("nohibernate", nohibernate_setup);
>  __setup("kaslr", kaslr_nohibernate_setup);
> +__setup("page_poison=", page_poison_nohibernate_setup);
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 25c98ae..3d3b954 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
>
>            If you are only interested in sanitization, say Y. Otherwise
>            say N.
> +
> +config PAGE_POISONING_ZERO
> +       bool "Use zero for poisoning instead of random data"
> +       depends on PAGE_POISONING
> +       ---help---
> +          Instead of using the existing poison value, fill the pages with
> +          zeros. This makes it harder to detect when errors are occurring
> +          due to sanitization but the zeroing at free means that it is
> +          no longer necessary to write zeros when GFP_ZERO is used on
> +          allocation.

May be worth noting the security benefit in this help text.

> +
> +          Enabling page poisoning with this option will disable hibernation

This isn't obvious to me. It looks like you need to both use
CONFIG_PAGE_POISOING_ZERO and put "page_poison=on" on the command line
to enable it?

-Kees

> +
> +          If unsure, say N
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cc4762a..59bd9dc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
>         return 0;
>  }
>
> +static inline bool free_pages_prezeroed(bool poisoned)
> +{
> +       return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
> +               page_poisoning_enabled() && poisoned;
> +}
> +
>  static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>                                                                 int alloc_flags)
>  {
>         int i;
> +       bool poisoned = true;
>
>         for (i = 0; i < (1 << order); i++) {
>                 struct page *p = page + i;
>                 if (unlikely(check_new_page(p)))
>                         return 1;
> +               if (poisoned)
> +                       poisoned &= page_is_poisoned(p);
>         }
>
>         set_page_private(page, 0);
> @@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>         kernel_poison_pages(page, 1 << order, 1);
>         kasan_alloc_pages(page, order);
>
> -       if (gfp_flags & __GFP_ZERO)
> +       if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
>                 for (i = 0; i < (1 << order); i++)
>                         clear_highpage(page + i);
>
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 292ca7b..2d864e6 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>         struct page_ext *base;
>
>         base = NODE_DATA(page_to_nid(page))->node_page_ext;
> -#ifdef CONFIG_DEBUG_VM
> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>         /*
>          * The sanity checks the page allocator does upon freeing a
>          * page can reach here before the page_ext arrays are
>          * allocated when feeding a range of pages to the allocator
>          * for the first time during bootup or memory hotplug.
> +        *
> +        * This check is also necessary for ensuring page poisoning
> +        * works as expected when enabled
>          */
>         if (unlikely(!base))
>                 return NULL;
> @@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>  {
>         unsigned long pfn = page_to_pfn(page);
>         struct mem_section *section = __pfn_to_section(pfn);
> -#ifdef CONFIG_DEBUG_VM
> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>         /*
>          * The sanity checks the page allocator does upon freeing a
>          * page can reach here before the page_ext arrays are
>          * allocated when feeding a range of pages to the allocator
>          * for the first time during bootup or memory hotplug.
> +        *
> +        * This check is also necessary for ensuring page poisoning
> +        * works as expected when enabled
>          */
>         if (!section->page_ext)
>                 return NULL;
> diff --git a/mm/page_poison.c b/mm/page_poison.c
> index 89d3bc7..479e7ea 100644
> --- a/mm/page_poison.c
> +++ b/mm/page_poison.c
> @@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
>         __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>  }
>
> -static inline bool page_poison(struct page *page)
> +bool page_is_poisoned(struct page *page)
>  {
>         struct page_ext *page_ext;
>
>         page_ext = lookup_page_ext(page);
> +       if (!page_ext)
> +               return false;
> +
>         return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>  }
>
> @@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
>  {
>         void *addr;
>
> -       if (!page_poison(page))
> +       if (!page_is_poisoned(page))
>                 return;
>
>         addr = kmap_atomic(page);
> --
> 2.5.0
>



-- 
Kees Cook
Chrome OS & Brillo Security

Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Kees Cook]

On Thu, Jan 28, 2016 at 6:38 PM, Laura Abbott <labbott@fedoraproject.org> wrote:
> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.
>
> Credit to Grsecurity/PaX team for inspiring this work
>
> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
> ---
>  include/linux/mm.h       |  2 ++
>  include/linux/poison.h   |  4 ++++
>  kernel/power/hibernate.c | 17 +++++++++++++++++
>  mm/Kconfig.debug         | 14 ++++++++++++++
>  mm/page_alloc.c          | 11 ++++++++++-
>  mm/page_ext.c            | 10 ++++++++--
>  mm/page_poison.c         |  7 +++++--
>  7 files changed, 60 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 966bf0e..59ce0dc 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>  #ifdef CONFIG_PAGE_POISONING
>  extern bool page_poisoning_enabled(void);
>  extern void kernel_poison_pages(struct page *page, int numpages, int enable);
> +extern bool page_is_poisoned(struct page *page);
>  #else
>  static inline bool page_poisoning_enabled(void) { return false; }
>  static inline void kernel_poison_pages(struct page *page, int numpages,
>                                         int enable) { }
> +static inline bool page_is_poisoned(struct page *page) { return false; }
>  #endif
>
>  #ifdef CONFIG_DEBUG_PAGEALLOC
> diff --git a/include/linux/poison.h b/include/linux/poison.h
> index 4a27153..51334ed 100644
> --- a/include/linux/poison.h
> +++ b/include/linux/poison.h
> @@ -30,7 +30,11 @@
>  #define TIMER_ENTRY_STATIC     ((void *) 0x300 + POISON_POINTER_DELTA)
>
>  /********** mm/debug-pagealloc.c **********/
> +#ifdef CONFIG_PAGE_POISONING_ZERO
> +#define PAGE_POISON 0x00
> +#else
>  #define PAGE_POISON 0xaa
> +#endif
>
>  /********** mm/page_alloc.c ************/
>
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index b7342a2..aa0f26b 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
>         return nohibernate_setup(str);
>  }
>
> +static int __init page_poison_nohibernate_setup(char *str)
> +{
> +#ifdef CONFIG_PAGE_POISONING_ZERO
> +       /*
> +        * The zeroing option for page poison skips the checks on alloc.
> +        * since hibernation doesn't save free pages there's no way to
> +        * guarantee the pages will still be zeroed.
> +        */
> +       if (!strcmp(str, "on")) {
> +               pr_info("Disabling hibernation due to page poisoning\n");
> +               return nohibernate_setup(str);
> +       }
> +#endif
> +       return 1;
> +}
> +
>  __setup("noresume", noresume_setup);
>  __setup("resume_offset=", resume_offset_setup);
>  __setup("resume=", resume_setup);
> @@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
>  __setup("resumedelay=", resumedelay_setup);
>  __setup("nohibernate", nohibernate_setup);
>  __setup("kaslr", kaslr_nohibernate_setup);
> +__setup("page_poison=", page_poison_nohibernate_setup);
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 25c98ae..3d3b954 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
>
>            If you are only interested in sanitization, say Y. Otherwise
>            say N.
> +
> +config PAGE_POISONING_ZERO
> +       bool "Use zero for poisoning instead of random data"
> +       depends on PAGE_POISONING
> +       ---help---
> +          Instead of using the existing poison value, fill the pages with
> +          zeros. This makes it harder to detect when errors are occurring
> +          due to sanitization but the zeroing at free means that it is
> +          no longer necessary to write zeros when GFP_ZERO is used on
> +          allocation.

May be worth noting the security benefit in this help text.

> +
> +          Enabling page poisoning with this option will disable hibernation

This isn't obvious to me. It looks like you need to both use
CONFIG_PAGE_POISOING_ZERO and put "page_poison=on" on the command line
to enable it?

-Kees

> +
> +          If unsure, say N
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cc4762a..59bd9dc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
>         return 0;
>  }
>
> +static inline bool free_pages_prezeroed(bool poisoned)
> +{
> +       return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
> +               page_poisoning_enabled() && poisoned;
> +}
> +
>  static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>                                                                 int alloc_flags)
>  {
>         int i;
> +       bool poisoned = true;
>
>         for (i = 0; i < (1 << order); i++) {
>                 struct page *p = page + i;
>                 if (unlikely(check_new_page(p)))
>                         return 1;
> +               if (poisoned)
> +                       poisoned &= page_is_poisoned(p);
>         }
>
>         set_page_private(page, 0);
> @@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>         kernel_poison_pages(page, 1 << order, 1);
>         kasan_alloc_pages(page, order);
>
> -       if (gfp_flags & __GFP_ZERO)
> +       if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
>                 for (i = 0; i < (1 << order); i++)
>                         clear_highpage(page + i);
>
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 292ca7b..2d864e6 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>         struct page_ext *base;
>
>         base = NODE_DATA(page_to_nid(page))->node_page_ext;
> -#ifdef CONFIG_DEBUG_VM
> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>         /*
>          * The sanity checks the page allocator does upon freeing a
>          * page can reach here before the page_ext arrays are
>          * allocated when feeding a range of pages to the allocator
>          * for the first time during bootup or memory hotplug.
> +        *
> +        * This check is also necessary for ensuring page poisoning
> +        * works as expected when enabled
>          */
>         if (unlikely(!base))
>                 return NULL;
> @@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>  {
>         unsigned long pfn = page_to_pfn(page);
>         struct mem_section *section = __pfn_to_section(pfn);
> -#ifdef CONFIG_DEBUG_VM
> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>         /*
>          * The sanity checks the page allocator does upon freeing a
>          * page can reach here before the page_ext arrays are
>          * allocated when feeding a range of pages to the allocator
>          * for the first time during bootup or memory hotplug.
> +        *
> +        * This check is also necessary for ensuring page poisoning
> +        * works as expected when enabled
>          */
>         if (!section->page_ext)
>                 return NULL;
> diff --git a/mm/page_poison.c b/mm/page_poison.c
> index 89d3bc7..479e7ea 100644
> --- a/mm/page_poison.c
> +++ b/mm/page_poison.c
> @@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
>         __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>  }
>
> -static inline bool page_poison(struct page *page)
> +bool page_is_poisoned(struct page *page)
>  {
>         struct page_ext *page_ext;
>
>         page_ext = lookup_page_ext(page);
> +       if (!page_ext)
> +               return false;
> +
>         return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>  }
>
> @@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
>  {
>         void *addr;
>
> -       if (!page_poison(page))
> +       if (!page_is_poisoned(page))
>                 return;
>
>         addr = kmap_atomic(page);
> --
> 2.5.0
>



-- 
Kees Cook
Chrome OS & Brillo Security

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Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

On 01/28/2016 08:46 PM, Kees Cook wrote:
> On Thu, Jan 28, 2016 at 6:38 PM, Laura Abbott <labbott@fedoraproject.org> wrote:
>> By default, page poisoning uses a poison value (0xaa) on free. If this
>> is changed to 0, the page is not only sanitized but zeroing on alloc
>> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
>> corruption from the poisoning is harder to detect. This feature also
>> cannot be used with hibernation since pages are not guaranteed to be
>> zeroed after hibernation.
>>
>> Credit to Grsecurity/PaX team for inspiring this work
>>
>> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
>> ---
>>   include/linux/mm.h       |  2 ++
>>   include/linux/poison.h   |  4 ++++
>>   kernel/power/hibernate.c | 17 +++++++++++++++++
>>   mm/Kconfig.debug         | 14 ++++++++++++++
>>   mm/page_alloc.c          | 11 ++++++++++-
>>   mm/page_ext.c            | 10 ++++++++--
>>   mm/page_poison.c         |  7 +++++--
>>   7 files changed, 60 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 966bf0e..59ce0dc 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>>   #ifdef CONFIG_PAGE_POISONING
>>   extern bool page_poisoning_enabled(void);
>>   extern void kernel_poison_pages(struct page *page, int numpages, int enable);
>> +extern bool page_is_poisoned(struct page *page);
>>   #else
>>   static inline bool page_poisoning_enabled(void) { return false; }
>>   static inline void kernel_poison_pages(struct page *page, int numpages,
>>                                          int enable) { }
>> +static inline bool page_is_poisoned(struct page *page) { return false; }
>>   #endif
>>
>>   #ifdef CONFIG_DEBUG_PAGEALLOC
>> diff --git a/include/linux/poison.h b/include/linux/poison.h
>> index 4a27153..51334ed 100644
>> --- a/include/linux/poison.h
>> +++ b/include/linux/poison.h
>> @@ -30,7 +30,11 @@
>>   #define TIMER_ENTRY_STATIC     ((void *) 0x300 + POISON_POINTER_DELTA)
>>
>>   /********** mm/debug-pagealloc.c **********/
>> +#ifdef CONFIG_PAGE_POISONING_ZERO
>> +#define PAGE_POISON 0x00
>> +#else
>>   #define PAGE_POISON 0xaa
>> +#endif
>>
>>   /********** mm/page_alloc.c ************/
>>
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index b7342a2..aa0f26b 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
>>          return nohibernate_setup(str);
>>   }
>>
>> +static int __init page_poison_nohibernate_setup(char *str)
>> +{
>> +#ifdef CONFIG_PAGE_POISONING_ZERO
>> +       /*
>> +        * The zeroing option for page poison skips the checks on alloc.
>> +        * since hibernation doesn't save free pages there's no way to
>> +        * guarantee the pages will still be zeroed.
>> +        */
>> +       if (!strcmp(str, "on")) {
>> +               pr_info("Disabling hibernation due to page poisoning\n");
>> +               return nohibernate_setup(str);
>> +       }
>> +#endif
>> +       return 1;
>> +}
>> +
>>   __setup("noresume", noresume_setup);
>>   __setup("resume_offset=", resume_offset_setup);
>>   __setup("resume=", resume_setup);
>> @@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
>>   __setup("resumedelay=", resumedelay_setup);
>>   __setup("nohibernate", nohibernate_setup);
>>   __setup("kaslr", kaslr_nohibernate_setup);
>> +__setup("page_poison=", page_poison_nohibernate_setup);
>> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
>> index 25c98ae..3d3b954 100644
>> --- a/mm/Kconfig.debug
>> +++ b/mm/Kconfig.debug
>> @@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
>>
>>             If you are only interested in sanitization, say Y. Otherwise
>>             say N.
>> +
>> +config PAGE_POISONING_ZERO
>> +       bool "Use zero for poisoning instead of random data"
>> +       depends on PAGE_POISONING
>> +       ---help---
>> +          Instead of using the existing poison value, fill the pages with
>> +          zeros. This makes it harder to detect when errors are occurring
>> +          due to sanitization but the zeroing at free means that it is
>> +          no longer necessary to write zeros when GFP_ZERO is used on
>> +          allocation.
>
> May be worth noting the security benefit in this help text.
>

This is supposed to build on the existing page poisoning which mentions the
security bit. I think this text needs to be clarified how this works.
  
>> +
>> +          Enabling page poisoning with this option will disable hibernation
>
> This isn't obvious to me. It looks like you need to both use
> CONFIG_PAGE_POISOING_ZERO and put "page_poison=on" on the command line
> to enable it?

Yeah, this isn't really clear. I'll make it more obvious this is an extension
of page poisoning so page poisoning must be enabled first.

>
> -Kees
>

Thanks,
Laura
  
>> +
>> +          If unsure, say N
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index cc4762a..59bd9dc 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
>>          return 0;
>>   }
>>
>> +static inline bool free_pages_prezeroed(bool poisoned)
>> +{
>> +       return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
>> +               page_poisoning_enabled() && poisoned;
>> +}
>> +
>>   static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>                                                                  int alloc_flags)
>>   {
>>          int i;
>> +       bool poisoned = true;
>>
>>          for (i = 0; i < (1 << order); i++) {
>>                  struct page *p = page + i;
>>                  if (unlikely(check_new_page(p)))
>>                          return 1;
>> +               if (poisoned)
>> +                       poisoned &= page_is_poisoned(p);
>>          }
>>
>>          set_page_private(page, 0);
>> @@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>          kernel_poison_pages(page, 1 << order, 1);
>>          kasan_alloc_pages(page, order);
>>
>> -       if (gfp_flags & __GFP_ZERO)
>> +       if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
>>                  for (i = 0; i < (1 << order); i++)
>>                          clear_highpage(page + i);
>>
>> diff --git a/mm/page_ext.c b/mm/page_ext.c
>> index 292ca7b..2d864e6 100644
>> --- a/mm/page_ext.c
>> +++ b/mm/page_ext.c
>> @@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>>          struct page_ext *base;
>>
>>          base = NODE_DATA(page_to_nid(page))->node_page_ext;
>> -#ifdef CONFIG_DEBUG_VM
>> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>>          /*
>>           * The sanity checks the page allocator does upon freeing a
>>           * page can reach here before the page_ext arrays are
>>           * allocated when feeding a range of pages to the allocator
>>           * for the first time during bootup or memory hotplug.
>> +        *
>> +        * This check is also necessary for ensuring page poisoning
>> +        * works as expected when enabled
>>           */
>>          if (unlikely(!base))
>>                  return NULL;
>> @@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>>   {
>>          unsigned long pfn = page_to_pfn(page);
>>          struct mem_section *section = __pfn_to_section(pfn);
>> -#ifdef CONFIG_DEBUG_VM
>> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>>          /*
>>           * The sanity checks the page allocator does upon freeing a
>>           * page can reach here before the page_ext arrays are
>>           * allocated when feeding a range of pages to the allocator
>>           * for the first time during bootup or memory hotplug.
>> +        *
>> +        * This check is also necessary for ensuring page poisoning
>> +        * works as expected when enabled
>>           */
>>          if (!section->page_ext)
>>                  return NULL;
>> diff --git a/mm/page_poison.c b/mm/page_poison.c
>> index 89d3bc7..479e7ea 100644
>> --- a/mm/page_poison.c
>> +++ b/mm/page_poison.c
>> @@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
>>          __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>>   }
>>
>> -static inline bool page_poison(struct page *page)
>> +bool page_is_poisoned(struct page *page)
>>   {
>>          struct page_ext *page_ext;
>>
>>          page_ext = lookup_page_ext(page);
>> +       if (!page_ext)
>> +               return false;
>> +
>>          return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>>   }
>>
>> @@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
>>   {
>>          void *addr;
>>
>> -       if (!page_poison(page))
>> +       if (!page_is_poisoned(page))
>>                  return;
>>
>>          addr = kmap_atomic(page);
>> --
>> 2.5.0
>>
>
>
>

[kernel-hardening] Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

On 01/28/2016 08:46 PM, Kees Cook wrote:
> On Thu, Jan 28, 2016 at 6:38 PM, Laura Abbott <labbott@fedoraproject.org> wrote:
>> By default, page poisoning uses a poison value (0xaa) on free. If this
>> is changed to 0, the page is not only sanitized but zeroing on alloc
>> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
>> corruption from the poisoning is harder to detect. This feature also
>> cannot be used with hibernation since pages are not guaranteed to be
>> zeroed after hibernation.
>>
>> Credit to Grsecurity/PaX team for inspiring this work
>>
>> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
>> ---
>>   include/linux/mm.h       |  2 ++
>>   include/linux/poison.h   |  4 ++++
>>   kernel/power/hibernate.c | 17 +++++++++++++++++
>>   mm/Kconfig.debug         | 14 ++++++++++++++
>>   mm/page_alloc.c          | 11 ++++++++++-
>>   mm/page_ext.c            | 10 ++++++++--
>>   mm/page_poison.c         |  7 +++++--
>>   7 files changed, 60 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 966bf0e..59ce0dc 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>>   #ifdef CONFIG_PAGE_POISONING
>>   extern bool page_poisoning_enabled(void);
>>   extern void kernel_poison_pages(struct page *page, int numpages, int enable);
>> +extern bool page_is_poisoned(struct page *page);
>>   #else
>>   static inline bool page_poisoning_enabled(void) { return false; }
>>   static inline void kernel_poison_pages(struct page *page, int numpages,
>>                                          int enable) { }
>> +static inline bool page_is_poisoned(struct page *page) { return false; }
>>   #endif
>>
>>   #ifdef CONFIG_DEBUG_PAGEALLOC
>> diff --git a/include/linux/poison.h b/include/linux/poison.h
>> index 4a27153..51334ed 100644
>> --- a/include/linux/poison.h
>> +++ b/include/linux/poison.h
>> @@ -30,7 +30,11 @@
>>   #define TIMER_ENTRY_STATIC     ((void *) 0x300 + POISON_POINTER_DELTA)
>>
>>   /********** mm/debug-pagealloc.c **********/
>> +#ifdef CONFIG_PAGE_POISONING_ZERO
>> +#define PAGE_POISON 0x00
>> +#else
>>   #define PAGE_POISON 0xaa
>> +#endif
>>
>>   /********** mm/page_alloc.c ************/
>>
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index b7342a2..aa0f26b 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
>>          return nohibernate_setup(str);
>>   }
>>
>> +static int __init page_poison_nohibernate_setup(char *str)
>> +{
>> +#ifdef CONFIG_PAGE_POISONING_ZERO
>> +       /*
>> +        * The zeroing option for page poison skips the checks on alloc.
>> +        * since hibernation doesn't save free pages there's no way to
>> +        * guarantee the pages will still be zeroed.
>> +        */
>> +       if (!strcmp(str, "on")) {
>> +               pr_info("Disabling hibernation due to page poisoning\n");
>> +               return nohibernate_setup(str);
>> +       }
>> +#endif
>> +       return 1;
>> +}
>> +
>>   __setup("noresume", noresume_setup);
>>   __setup("resume_offset=", resume_offset_setup);
>>   __setup("resume=", resume_setup);
>> @@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
>>   __setup("resumedelay=", resumedelay_setup);
>>   __setup("nohibernate", nohibernate_setup);
>>   __setup("kaslr", kaslr_nohibernate_setup);
>> +__setup("page_poison=", page_poison_nohibernate_setup);
>> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
>> index 25c98ae..3d3b954 100644
>> --- a/mm/Kconfig.debug
>> +++ b/mm/Kconfig.debug
>> @@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
>>
>>             If you are only interested in sanitization, say Y. Otherwise
>>             say N.
>> +
>> +config PAGE_POISONING_ZERO
>> +       bool "Use zero for poisoning instead of random data"
>> +       depends on PAGE_POISONING
>> +       ---help---
>> +          Instead of using the existing poison value, fill the pages with
>> +          zeros. This makes it harder to detect when errors are occurring
>> +          due to sanitization but the zeroing at free means that it is
>> +          no longer necessary to write zeros when GFP_ZERO is used on
>> +          allocation.
>
> May be worth noting the security benefit in this help text.
>

This is supposed to build on the existing page poisoning which mentions the
security bit. I think this text needs to be clarified how this works.
  
>> +
>> +          Enabling page poisoning with this option will disable hibernation
>
> This isn't obvious to me. It looks like you need to both use
> CONFIG_PAGE_POISOING_ZERO and put "page_poison=on" on the command line
> to enable it?

Yeah, this isn't really clear. I'll make it more obvious this is an extension
of page poisoning so page poisoning must be enabled first.

>
> -Kees
>

Thanks,
Laura
  
>> +
>> +          If unsure, say N
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index cc4762a..59bd9dc 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
>>          return 0;
>>   }
>>
>> +static inline bool free_pages_prezeroed(bool poisoned)
>> +{
>> +       return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
>> +               page_poisoning_enabled() && poisoned;
>> +}
>> +
>>   static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>                                                                  int alloc_flags)
>>   {
>>          int i;
>> +       bool poisoned = true;
>>
>>          for (i = 0; i < (1 << order); i++) {
>>                  struct page *p = page + i;
>>                  if (unlikely(check_new_page(p)))
>>                          return 1;
>> +               if (poisoned)
>> +                       poisoned &= page_is_poisoned(p);
>>          }
>>
>>          set_page_private(page, 0);
>> @@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>          kernel_poison_pages(page, 1 << order, 1);
>>          kasan_alloc_pages(page, order);
>>
>> -       if (gfp_flags & __GFP_ZERO)
>> +       if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
>>                  for (i = 0; i < (1 << order); i++)
>>                          clear_highpage(page + i);
>>
>> diff --git a/mm/page_ext.c b/mm/page_ext.c
>> index 292ca7b..2d864e6 100644
>> --- a/mm/page_ext.c
>> +++ b/mm/page_ext.c
>> @@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>>          struct page_ext *base;
>>
>>          base = NODE_DATA(page_to_nid(page))->node_page_ext;
>> -#ifdef CONFIG_DEBUG_VM
>> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>>          /*
>>           * The sanity checks the page allocator does upon freeing a
>>           * page can reach here before the page_ext arrays are
>>           * allocated when feeding a range of pages to the allocator
>>           * for the first time during bootup or memory hotplug.
>> +        *
>> +        * This check is also necessary for ensuring page poisoning
>> +        * works as expected when enabled
>>           */
>>          if (unlikely(!base))
>>                  return NULL;
>> @@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>>   {
>>          unsigned long pfn = page_to_pfn(page);
>>          struct mem_section *section = __pfn_to_section(pfn);
>> -#ifdef CONFIG_DEBUG_VM
>> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>>          /*
>>           * The sanity checks the page allocator does upon freeing a
>>           * page can reach here before the page_ext arrays are
>>           * allocated when feeding a range of pages to the allocator
>>           * for the first time during bootup or memory hotplug.
>> +        *
>> +        * This check is also necessary for ensuring page poisoning
>> +        * works as expected when enabled
>>           */
>>          if (!section->page_ext)
>>                  return NULL;
>> diff --git a/mm/page_poison.c b/mm/page_poison.c
>> index 89d3bc7..479e7ea 100644
>> --- a/mm/page_poison.c
>> +++ b/mm/page_poison.c
>> @@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
>>          __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>>   }
>>
>> -static inline bool page_poison(struct page *page)
>> +bool page_is_poisoned(struct page *page)
>>   {
>>          struct page_ext *page_ext;
>>
>>          page_ext = lookup_page_ext(page);
>> +       if (!page_ext)
>> +               return false;
>> +
>>          return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>>   }
>>
>> @@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
>>   {
>>          void *addr;
>>
>> -       if (!page_poison(page))
>> +       if (!page_is_poisoned(page))
>>                  return;
>>
>>          addr = kmap_atomic(page);
>> --
>> 2.5.0
>>
>
>
>

Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

On 01/28/2016 08:46 PM, Kees Cook wrote:
> On Thu, Jan 28, 2016 at 6:38 PM, Laura Abbott <labbott@fedoraproject.org> wrote:
>> By default, page poisoning uses a poison value (0xaa) on free. If this
>> is changed to 0, the page is not only sanitized but zeroing on alloc
>> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
>> corruption from the poisoning is harder to detect. This feature also
>> cannot be used with hibernation since pages are not guaranteed to be
>> zeroed after hibernation.
>>
>> Credit to Grsecurity/PaX team for inspiring this work
>>
>> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
>> ---
>>   include/linux/mm.h       |  2 ++
>>   include/linux/poison.h   |  4 ++++
>>   kernel/power/hibernate.c | 17 +++++++++++++++++
>>   mm/Kconfig.debug         | 14 ++++++++++++++
>>   mm/page_alloc.c          | 11 ++++++++++-
>>   mm/page_ext.c            | 10 ++++++++--
>>   mm/page_poison.c         |  7 +++++--
>>   7 files changed, 60 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 966bf0e..59ce0dc 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>>   #ifdef CONFIG_PAGE_POISONING
>>   extern bool page_poisoning_enabled(void);
>>   extern void kernel_poison_pages(struct page *page, int numpages, int enable);
>> +extern bool page_is_poisoned(struct page *page);
>>   #else
>>   static inline bool page_poisoning_enabled(void) { return false; }
>>   static inline void kernel_poison_pages(struct page *page, int numpages,
>>                                          int enable) { }
>> +static inline bool page_is_poisoned(struct page *page) { return false; }
>>   #endif
>>
>>   #ifdef CONFIG_DEBUG_PAGEALLOC
>> diff --git a/include/linux/poison.h b/include/linux/poison.h
>> index 4a27153..51334ed 100644
>> --- a/include/linux/poison.h
>> +++ b/include/linux/poison.h
>> @@ -30,7 +30,11 @@
>>   #define TIMER_ENTRY_STATIC     ((void *) 0x300 + POISON_POINTER_DELTA)
>>
>>   /********** mm/debug-pagealloc.c **********/
>> +#ifdef CONFIG_PAGE_POISONING_ZERO
>> +#define PAGE_POISON 0x00
>> +#else
>>   #define PAGE_POISON 0xaa
>> +#endif
>>
>>   /********** mm/page_alloc.c ************/
>>
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index b7342a2..aa0f26b 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
>>          return nohibernate_setup(str);
>>   }
>>
>> +static int __init page_poison_nohibernate_setup(char *str)
>> +{
>> +#ifdef CONFIG_PAGE_POISONING_ZERO
>> +       /*
>> +        * The zeroing option for page poison skips the checks on alloc.
>> +        * since hibernation doesn't save free pages there's no way to
>> +        * guarantee the pages will still be zeroed.
>> +        */
>> +       if (!strcmp(str, "on")) {
>> +               pr_info("Disabling hibernation due to page poisoning\n");
>> +               return nohibernate_setup(str);
>> +       }
>> +#endif
>> +       return 1;
>> +}
>> +
>>   __setup("noresume", noresume_setup);
>>   __setup("resume_offset=", resume_offset_setup);
>>   __setup("resume=", resume_setup);
>> @@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
>>   __setup("resumedelay=", resumedelay_setup);
>>   __setup("nohibernate", nohibernate_setup);
>>   __setup("kaslr", kaslr_nohibernate_setup);
>> +__setup("page_poison=", page_poison_nohibernate_setup);
>> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
>> index 25c98ae..3d3b954 100644
>> --- a/mm/Kconfig.debug
>> +++ b/mm/Kconfig.debug
>> @@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
>>
>>             If you are only interested in sanitization, say Y. Otherwise
>>             say N.
>> +
>> +config PAGE_POISONING_ZERO
>> +       bool "Use zero for poisoning instead of random data"
>> +       depends on PAGE_POISONING
>> +       ---help---
>> +          Instead of using the existing poison value, fill the pages with
>> +          zeros. This makes it harder to detect when errors are occurring
>> +          due to sanitization but the zeroing at free means that it is
>> +          no longer necessary to write zeros when GFP_ZERO is used on
>> +          allocation.
>
> May be worth noting the security benefit in this help text.
>

This is supposed to build on the existing page poisoning which mentions the
security bit. I think this text needs to be clarified how this works.
  
>> +
>> +          Enabling page poisoning with this option will disable hibernation
>
> This isn't obvious to me. It looks like you need to both use
> CONFIG_PAGE_POISOING_ZERO and put "page_poison=on" on the command line
> to enable it?

Yeah, this isn't really clear. I'll make it more obvious this is an extension
of page poisoning so page poisoning must be enabled first.

>
> -Kees
>

Thanks,
Laura
  
>> +
>> +          If unsure, say N
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index cc4762a..59bd9dc 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
>>          return 0;
>>   }
>>
>> +static inline bool free_pages_prezeroed(bool poisoned)
>> +{
>> +       return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
>> +               page_poisoning_enabled() && poisoned;
>> +}
>> +
>>   static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>                                                                  int alloc_flags)
>>   {
>>          int i;
>> +       bool poisoned = true;
>>
>>          for (i = 0; i < (1 << order); i++) {
>>                  struct page *p = page + i;
>>                  if (unlikely(check_new_page(p)))
>>                          return 1;
>> +               if (poisoned)
>> +                       poisoned &= page_is_poisoned(p);
>>          }
>>
>>          set_page_private(page, 0);
>> @@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>          kernel_poison_pages(page, 1 << order, 1);
>>          kasan_alloc_pages(page, order);
>>
>> -       if (gfp_flags & __GFP_ZERO)
>> +       if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
>>                  for (i = 0; i < (1 << order); i++)
>>                          clear_highpage(page + i);
>>
>> diff --git a/mm/page_ext.c b/mm/page_ext.c
>> index 292ca7b..2d864e6 100644
>> --- a/mm/page_ext.c
>> +++ b/mm/page_ext.c
>> @@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>>          struct page_ext *base;
>>
>>          base = NODE_DATA(page_to_nid(page))->node_page_ext;
>> -#ifdef CONFIG_DEBUG_VM
>> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>>          /*
>>           * The sanity checks the page allocator does upon freeing a
>>           * page can reach here before the page_ext arrays are
>>           * allocated when feeding a range of pages to the allocator
>>           * for the first time during bootup or memory hotplug.
>> +        *
>> +        * This check is also necessary for ensuring page poisoning
>> +        * works as expected when enabled
>>           */
>>          if (unlikely(!base))
>>                  return NULL;
>> @@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>>   {
>>          unsigned long pfn = page_to_pfn(page);
>>          struct mem_section *section = __pfn_to_section(pfn);
>> -#ifdef CONFIG_DEBUG_VM
>> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>>          /*
>>           * The sanity checks the page allocator does upon freeing a
>>           * page can reach here before the page_ext arrays are
>>           * allocated when feeding a range of pages to the allocator
>>           * for the first time during bootup or memory hotplug.
>> +        *
>> +        * This check is also necessary for ensuring page poisoning
>> +        * works as expected when enabled
>>           */
>>          if (!section->page_ext)
>>                  return NULL;
>> diff --git a/mm/page_poison.c b/mm/page_poison.c
>> index 89d3bc7..479e7ea 100644
>> --- a/mm/page_poison.c
>> +++ b/mm/page_poison.c
>> @@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
>>          __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>>   }
>>
>> -static inline bool page_poison(struct page *page)
>> +bool page_is_poisoned(struct page *page)
>>   {
>>          struct page_ext *page_ext;
>>
>>          page_ext = lookup_page_ext(page);
>> +       if (!page_ext)
>> +               return false;
>> +
>>          return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>>   }
>>
>> @@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
>>   {
>>          void *addr;
>>
>> -       if (!page_poison(page))
>> +       if (!page_is_poisoned(page))
>>                  return;
>>
>>          addr = kmap_atomic(page);
>> --
>> 2.5.0
>>
>
>
>

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Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

On 01/28/2016 08:46 PM, Kees Cook wrote:
> On Thu, Jan 28, 2016 at 6:38 PM, Laura Abbott <labbott@fedoraproject.org> wrote:
>> By default, page poisoning uses a poison value (0xaa) on free. If this
>> is changed to 0, the page is not only sanitized but zeroing on alloc
>> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
>> corruption from the poisoning is harder to detect. This feature also
>> cannot be used with hibernation since pages are not guaranteed to be
>> zeroed after hibernation.
>>
>> Credit to Grsecurity/PaX team for inspiring this work
>>
>> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
>> ---
>>   include/linux/mm.h       |  2 ++
>>   include/linux/poison.h   |  4 ++++
>>   kernel/power/hibernate.c | 17 +++++++++++++++++
>>   mm/Kconfig.debug         | 14 ++++++++++++++
>>   mm/page_alloc.c          | 11 ++++++++++-
>>   mm/page_ext.c            | 10 ++++++++--
>>   mm/page_poison.c         |  7 +++++--
>>   7 files changed, 60 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 966bf0e..59ce0dc 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2177,10 +2177,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>>   #ifdef CONFIG_PAGE_POISONING
>>   extern bool page_poisoning_enabled(void);
>>   extern void kernel_poison_pages(struct page *page, int numpages, int enable);
>> +extern bool page_is_poisoned(struct page *page);
>>   #else
>>   static inline bool page_poisoning_enabled(void) { return false; }
>>   static inline void kernel_poison_pages(struct page *page, int numpages,
>>                                          int enable) { }
>> +static inline bool page_is_poisoned(struct page *page) { return false; }
>>   #endif
>>
>>   #ifdef CONFIG_DEBUG_PAGEALLOC
>> diff --git a/include/linux/poison.h b/include/linux/poison.h
>> index 4a27153..51334ed 100644
>> --- a/include/linux/poison.h
>> +++ b/include/linux/poison.h
>> @@ -30,7 +30,11 @@
>>   #define TIMER_ENTRY_STATIC     ((void *) 0x300 + POISON_POINTER_DELTA)
>>
>>   /********** mm/debug-pagealloc.c **********/
>> +#ifdef CONFIG_PAGE_POISONING_ZERO
>> +#define PAGE_POISON 0x00
>> +#else
>>   #define PAGE_POISON 0xaa
>> +#endif
>>
>>   /********** mm/page_alloc.c ************/
>>
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index b7342a2..aa0f26b 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str)
>>          return nohibernate_setup(str);
>>   }
>>
>> +static int __init page_poison_nohibernate_setup(char *str)
>> +{
>> +#ifdef CONFIG_PAGE_POISONING_ZERO
>> +       /*
>> +        * The zeroing option for page poison skips the checks on alloc.
>> +        * since hibernation doesn't save free pages there's no way to
>> +        * guarantee the pages will still be zeroed.
>> +        */
>> +       if (!strcmp(str, "on")) {
>> +               pr_info("Disabling hibernation due to page poisoning\n");
>> +               return nohibernate_setup(str);
>> +       }
>> +#endif
>> +       return 1;
>> +}
>> +
>>   __setup("noresume", noresume_setup);
>>   __setup("resume_offset=", resume_offset_setup);
>>   __setup("resume=", resume_setup);
>> @@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup);
>>   __setup("resumedelay=", resumedelay_setup);
>>   __setup("nohibernate", nohibernate_setup);
>>   __setup("kaslr", kaslr_nohibernate_setup);
>> +__setup("page_poison=", page_poison_nohibernate_setup);
>> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
>> index 25c98ae..3d3b954 100644
>> --- a/mm/Kconfig.debug
>> +++ b/mm/Kconfig.debug
>> @@ -48,3 +48,17 @@ config PAGE_POISONING_NO_SANITY
>>
>>             If you are only interested in sanitization, say Y. Otherwise
>>             say N.
>> +
>> +config PAGE_POISONING_ZERO
>> +       bool "Use zero for poisoning instead of random data"
>> +       depends on PAGE_POISONING
>> +       ---help---
>> +          Instead of using the existing poison value, fill the pages with
>> +          zeros. This makes it harder to detect when errors are occurring
>> +          due to sanitization but the zeroing at free means that it is
>> +          no longer necessary to write zeros when GFP_ZERO is used on
>> +          allocation.
>
> May be worth noting the security benefit in this help text.
>

This is supposed to build on the existing page poisoning which mentions the
security bit. I think this text needs to be clarified how this works.
  
>> +
>> +          Enabling page poisoning with this option will disable hibernation
>
> This isn't obvious to me. It looks like you need to both use
> CONFIG_PAGE_POISOING_ZERO and put "page_poison=on" on the command line
> to enable it?

Yeah, this isn't really clear. I'll make it more obvious this is an extension
of page poisoning so page poisoning must be enabled first.

>
> -Kees
>

Thanks,
Laura
  
>> +
>> +          If unsure, say N
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index cc4762a..59bd9dc 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1382,15 +1382,24 @@ static inline int check_new_page(struct page *page)
>>          return 0;
>>   }
>>
>> +static inline bool free_pages_prezeroed(bool poisoned)
>> +{
>> +       return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
>> +               page_poisoning_enabled() && poisoned;
>> +}
>> +
>>   static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>                                                                  int alloc_flags)
>>   {
>>          int i;
>> +       bool poisoned = true;
>>
>>          for (i = 0; i < (1 << order); i++) {
>>                  struct page *p = page + i;
>>                  if (unlikely(check_new_page(p)))
>>                          return 1;
>> +               if (poisoned)
>> +                       poisoned &= page_is_poisoned(p);
>>          }
>>
>>          set_page_private(page, 0);
>> @@ -1401,7 +1410,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>>          kernel_poison_pages(page, 1 << order, 1);
>>          kasan_alloc_pages(page, order);
>>
>> -       if (gfp_flags & __GFP_ZERO)
>> +       if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
>>                  for (i = 0; i < (1 << order); i++)
>>                          clear_highpage(page + i);
>>
>> diff --git a/mm/page_ext.c b/mm/page_ext.c
>> index 292ca7b..2d864e6 100644
>> --- a/mm/page_ext.c
>> +++ b/mm/page_ext.c
>> @@ -106,12 +106,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>>          struct page_ext *base;
>>
>>          base = NODE_DATA(page_to_nid(page))->node_page_ext;
>> -#ifdef CONFIG_DEBUG_VM
>> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>>          /*
>>           * The sanity checks the page allocator does upon freeing a
>>           * page can reach here before the page_ext arrays are
>>           * allocated when feeding a range of pages to the allocator
>>           * for the first time during bootup or memory hotplug.
>> +        *
>> +        * This check is also necessary for ensuring page poisoning
>> +        * works as expected when enabled
>>           */
>>          if (unlikely(!base))
>>                  return NULL;
>> @@ -180,12 +183,15 @@ struct page_ext *lookup_page_ext(struct page *page)
>>   {
>>          unsigned long pfn = page_to_pfn(page);
>>          struct mem_section *section = __pfn_to_section(pfn);
>> -#ifdef CONFIG_DEBUG_VM
>> +#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>>          /*
>>           * The sanity checks the page allocator does upon freeing a
>>           * page can reach here before the page_ext arrays are
>>           * allocated when feeding a range of pages to the allocator
>>           * for the first time during bootup or memory hotplug.
>> +        *
>> +        * This check is also necessary for ensuring page poisoning
>> +        * works as expected when enabled
>>           */
>>          if (!section->page_ext)
>>                  return NULL;
>> diff --git a/mm/page_poison.c b/mm/page_poison.c
>> index 89d3bc7..479e7ea 100644
>> --- a/mm/page_poison.c
>> +++ b/mm/page_poison.c
>> @@ -71,11 +71,14 @@ static inline void clear_page_poison(struct page *page)
>>          __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>>   }
>>
>> -static inline bool page_poison(struct page *page)
>> +bool page_is_poisoned(struct page *page)
>>   {
>>          struct page_ext *page_ext;
>>
>>          page_ext = lookup_page_ext(page);
>> +       if (!page_ext)
>> +               return false;
>> +
>>          return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
>>   }
>>
>> @@ -137,7 +140,7 @@ static void unpoison_page(struct page *page)
>>   {
>>          void *addr;
>>
>> -       if (!page_poison(page))
>> +       if (!page_is_poisoned(page))
>>                  return;
>>
>>          addr = kmap_atomic(page);
>> --
>> 2.5.0
>>
>
>
>

Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Pavel Machek]

Hi!

> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.

So... this makes kernel harder to debug for performance advantage...?
If so.. how big is the performance advantage?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

[kernel-hardening] Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Pavel Machek]

Hi!

> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.

So... this makes kernel harder to debug for performance advantage...?
If so.. how big is the performance advantage?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Pavel Machek]

Hi!

> By default, page poisoning uses a poison value (0xaa) on free. If this
> is changed to 0, the page is not only sanitized but zeroing on alloc
> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> corruption from the poisoning is harder to detect. This feature also
> cannot be used with hibernation since pages are not guaranteed to be
> zeroed after hibernation.

So... this makes kernel harder to debug for performance advantage...?
If so.. how big is the performance advantage?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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To unsubscribe, send a message with 'unsubscribe linux-mm' in
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Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

On 01/29/2016 02:45 AM, Pavel Machek wrote:
> Hi!
>
>> By default, page poisoning uses a poison value (0xaa) on free. If this
>> is changed to 0, the page is not only sanitized but zeroing on alloc
>> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
>> corruption from the poisoning is harder to detect. This feature also
>> cannot be used with hibernation since pages are not guaranteed to be
>> zeroed after hibernation.
>
> So... this makes kernel harder to debug for performance advantage...?
> If so.. how big is the performance advantage?
> 									Pavel
>

The performance advantage really depends on the benchmark you are running.
It was pointed out this may help some unknown amount with merging pages
in VMs since the pages are now identical and can be merged. The debugging
is also only slightly more difficult. With the non-zero poisoning value
it's easier to see that a crash was caused by triggering the poison vs.
just some random NULL pointer.

As as been pointed out, this help text could use some updating so I'll
clarify this more.

Thanks,
Laura

[kernel-hardening] Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

On 01/29/2016 02:45 AM, Pavel Machek wrote:
> Hi!
>
>> By default, page poisoning uses a poison value (0xaa) on free. If this
>> is changed to 0, the page is not only sanitized but zeroing on alloc
>> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
>> corruption from the poisoning is harder to detect. This feature also
>> cannot be used with hibernation since pages are not guaranteed to be
>> zeroed after hibernation.
>
> So... this makes kernel harder to debug for performance advantage...?
> If so.. how big is the performance advantage?
> 									Pavel
>

The performance advantage really depends on the benchmark you are running.
It was pointed out this may help some unknown amount with merging pages
in VMs since the pages are now identical and can be merged. The debugging
is also only slightly more difficult. With the non-zero poisoning value
it's easier to see that a crash was caused by triggering the poison vs.
just some random NULL pointer.

As as been pointed out, this help text could use some updating so I'll
clarify this more.

Thanks,
Laura

Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Laura Abbott]

On 01/29/2016 02:45 AM, Pavel Machek wrote:
> Hi!
>
>> By default, page poisoning uses a poison value (0xaa) on free. If this
>> is changed to 0, the page is not only sanitized but zeroing on alloc
>> with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
>> corruption from the poisoning is harder to detect. This feature also
>> cannot be used with hibernation since pages are not guaranteed to be
>> zeroed after hibernation.
>
> So... this makes kernel harder to debug for performance advantage...?
> If so.. how big is the performance advantage?
> 									Pavel
>

The performance advantage really depends on the benchmark you are running.
It was pointed out this may help some unknown amount with merging pages
in VMs since the pages are now identical and can be merged. The debugging
is also only slightly more difficult. With the non-zero poisoning value
it's easier to see that a crash was caused by triggering the poison vs.
just some random NULL pointer.

As as been pointed out, this help text could use some updating so I'll
clarify this more.

Thanks,
Laura

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Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Pavel Machek]

Hi!

> >>By default, page poisoning uses a poison value (0xaa) on free. If this
> >>is changed to 0, the page is not only sanitized but zeroing on alloc
> >>with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> >>corruption from the poisoning is harder to detect. This feature also
> >>cannot be used with hibernation since pages are not guaranteed to be
> >>zeroed after hibernation.
> >
> >So... this makes kernel harder to debug for performance advantage...?
> >If so.. how big is the performance advantage?

> 
> The performance advantage really depends on the benchmark you are
> running.

You are trying to improve performance, so you should publish at least
one benchmark where it helps.

Alternatively, quote kernel build times with and without the
patch.

If it speeds kernel compile twice, I guess I may even help with
hibernation support. If it makes kernel compile faster by .00000034%
(or slows it down), we should probably simply ignore this patch.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

[kernel-hardening] Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Pavel Machek]

Hi!

> >>By default, page poisoning uses a poison value (0xaa) on free. If this
> >>is changed to 0, the page is not only sanitized but zeroing on alloc
> >>with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> >>corruption from the poisoning is harder to detect. This feature also
> >>cannot be used with hibernation since pages are not guaranteed to be
> >>zeroed after hibernation.
> >
> >So... this makes kernel harder to debug for performance advantage...?
> >If so.. how big is the performance advantage?

> 
> The performance advantage really depends on the benchmark you are
> running.

You are trying to improve performance, so you should publish at least
one benchmark where it helps.

Alternatively, quote kernel build times with and without the
patch.

If it speeds kernel compile twice, I guess I may even help with
hibernation support. If it makes kernel compile faster by .00000034%
(or slows it down), we should probably simply ignore this patch.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [PATCHv2 2/2] mm/page_poisoning.c: Allow for zero poisoning

[Pavel Machek]

Hi!

> >>By default, page poisoning uses a poison value (0xaa) on free. If this
> >>is changed to 0, the page is not only sanitized but zeroing on alloc
> >>with __GFP_ZERO can be skipped as well. The tradeoff is that detecting
> >>corruption from the poisoning is harder to detect. This feature also
> >>cannot be used with hibernation since pages are not guaranteed to be
> >>zeroed after hibernation.
> >
> >So... this makes kernel harder to debug for performance advantage...?
> >If so.. how big is the performance advantage?

> 
> The performance advantage really depends on the benchmark you are
> running.

You are trying to improve performance, so you should publish at least
one benchmark where it helps.

Alternatively, quote kernel build times with and without the
patch.

If it speeds kernel compile twice, I guess I may even help with
hibernation support. If it makes kernel compile faster by .00000034%
(or slows it down), we should probably simply ignore this patch.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>