mm/page_poison.c: enable PAGE_POISONING as a separate option
Page poisoning is currently set up 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
kernel_map pages since the two features do separate work. Because of
how hiberanation is implemented, the checks on alloc cannot occur if
hibernation is enabled. The runtime alloc checks can also be enabled
with an option when !HIBERNATION.
Credit to Grsecurity/PaX team for inspiring this work
Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mathias Krause <minipli@googlemail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Jianyu Zhan <nasa4836@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index a0c136a..1f99f9a 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -41,4 +41,27 @@
can be overridden by debug_pagealloc=off|on.
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.
+
+ Note that "poison" here is not the same thing as the "HWPoison"
+ for CONFIG_MEMORY_FAILURE. This is software poisoning only.
+
+ 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-$(CONFIG_SLOB) += slob.o
obj-$(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/page_alloc.c b/mm/page_alloc.c
index 0691403..2a08349 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1025,6 +1025,7 @@
PAGE_SIZE << order);
}
arch_free_page(page, order);
+ kernel_poison_pages(page, 1 << order, 0);
kernel_map_pages(page, 1 << order, 0);
return true;
@@ -1420,6 +1421,7 @@
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/debug-pagealloc.c b/mm/page_poison.c
similarity index 66%
rename from mm/debug-pagealloc.c
rename to mm/page_poison.c
index 5bf5906..89d3bc7 100644
--- a/mm/debug-pagealloc.c
+++ b/mm/page_poison.c
@@ -6,22 +6,48 @@
#include <linux/poison.h>
#include <linux/ratelimit.h>
-static bool page_poisoning_enabled __read_mostly;
+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)
{
- if (!debug_pagealloc_enabled())
- return false;
-
- return true;
+ return want_page_poisoning;
}
static void init_page_poisoning(void)
{
- if (!debug_pagealloc_enabled())
- return;
+ /*
+ * 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;
+ __page_poisoning_enabled = true;
}
struct page_ext_operations page_poisoning_ops = {
@@ -83,6 +109,9 @@
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;
@@ -95,9 +124,9 @@
if (!__ratelimit(&ratelimit))
return;
else if (start == end && single_bit_flip(*start, PAGE_POISON))
- printk(KERN_ERR "pagealloc: single bit error\n");
+ pr_err("pagealloc: single bit error\n");
else
- printk(KERN_ERR "pagealloc: memory corruption\n");
+ pr_err("pagealloc: memory corruption\n");
print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
end - start + 1, 1);
@@ -125,9 +154,9 @@
unpoison_page(page + i);
}
-void __kernel_map_pages(struct page *page, int numpages, int enable)
+void kernel_poison_pages(struct page *page, int numpages, int enable)
{
- if (!page_poisoning_enabled)
+ if (!page_poisoning_enabled())
return;
if (enable)
@@ -135,3 +164,10 @@
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