[PATCH v7 0/5] kasan: support backing vmalloc space with real shadow memory

[PATCH v7 0/5] kasan: support backing vmalloc space with real shadow memory

[Daniel Axtens]

Currently, vmalloc space is backed by the early shadow page. This
means that kasan is incompatible with VMAP_STACK.

This series provides a mechanism to back vmalloc space with real,
dynamically allocated memory. I have only wired up x86, because that's
the only currently supported arch I can work with easily, but it's
very easy to wire up other architectures, and it appears that there is
some work-in-progress code to do this on arm64 and s390.

This has been discussed before in the context of VMAP_STACK:
 - https://bugzilla.kernel.org/show_bug.cgi?id=202009
 - https://lkml.org/lkml/2018/7/22/198
 - https://lkml.org/lkml/2019/7/19/822

In terms of implementation details:

Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.

Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.

We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.


v1: https://lore.kernel.org/linux-mm/20190725055503.19507-1-dja@axtens.net/
v2: https://lore.kernel.org/linux-mm/20190729142108.23343-1-dja@axtens.net/
 Address review comments:
 - Patch 1: use kasan_unpoison_shadow's built-in handling of
            ranges that do not align to a full shadow byte
 - Patch 3: prepopulate pgds rather than faulting things in
v3: https://lore.kernel.org/linux-mm/20190731071550.31814-1-dja@axtens.net/
 Address comments from Mark Rutland:
 - kasan_populate_vmalloc is a better name
 - handle concurrency correctly
 - various nits and cleanups
 - relax module alignment in KASAN_VMALLOC case
v4: https://lore.kernel.org/linux-mm/20190815001636.12235-1-dja@axtens.net/
 Changes to patch 1 only:
 - Integrate Mark's rework, thanks Mark!
 - handle the case where kasan_populate_shadow might fail
 - poision shadow on free, allowing the alloc path to just
     unpoision memory that it uses
v5: https://lore.kernel.org/linux-mm/20190830003821.10737-1-dja@axtens.net/
 Address comments from Christophe Leroy:
 - Fix some issues with my descriptions in commit messages and docs
 - Dynamically free unused shadow pages by hooking into the vmap book-keeping
 - Split out the test into a separate patch
 - Optional patch to track the number of pages allocated
 - minor checkpatch cleanups
v6: https://lore.kernel.org/linux-mm/20190902112028.23773-1-dja@axtens.net/
 Properly guard freeing pages in patch 1, drop debugging code.
v7: Add a TLB flush on freeing, thanks Mark Rutland.
    Explain more clearly how I think freeing is concurrency-safe.

Daniel Axtens (5):
  kasan: support backing vmalloc space with real shadow memory
  kasan: add test for vmalloc
  fork: support VMAP_STACK with KASAN_VMALLOC
  x86/kasan: support KASAN_VMALLOC
  kasan debug: track pages allocated for vmalloc shadow

 Documentation/dev-tools/kasan.rst |  63 ++++++++
 arch/Kconfig                      |   9 +-
 arch/x86/Kconfig                  |   1 +
 arch/x86/mm/kasan_init_64.c       |  60 ++++++++
 include/linux/kasan.h             |  31 ++++
 include/linux/moduleloader.h      |   2 +-
 include/linux/vmalloc.h           |  12 ++
 kernel/fork.c                     |   4 +
 lib/Kconfig.kasan                 |  16 +++
 lib/test_kasan.c                  |  26 ++++
 mm/kasan/common.c                 | 230 ++++++++++++++++++++++++++++++
 mm/kasan/generic_report.c         |   3 +
 mm/kasan/kasan.h                  |   1 +
 mm/vmalloc.c                      |  45 +++++-
 14 files changed, 497 insertions(+), 6 deletions(-)

-- 
2.20.1

[PATCH v7 1/5] kasan: support backing vmalloc space with real shadow memory

[Daniel Axtens]

Hook into vmalloc and vmap, and dynamically allocate real shadow
memory to back the mappings.

Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.

Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.

We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.

To avoid the difficulties around swapping mappings around, this code
expects that the part of the shadow region that covers the vmalloc
space will not be covered by the early shadow page, but will be left
unmapped. This will require changes in arch-specific code.

This allows KASAN with VMAP_STACK, and may be helpful for architectures
that do not have a separate module space (e.g. powerpc64, which I am
currently working on). It also allows relaxing the module alignment
back to PAGE_SIZE.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=202009
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
[Mark: rework shadow allocation]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>

--

v2: let kasan_unpoison_shadow deal with ranges that do not use a
    full shadow byte.

v3: relax module alignment
    rename to kasan_populate_vmalloc which is a much better name
    deal with concurrency correctly

v4: Mark's rework
    Poision pages on vfree
    Handle allocation failures

v5: Per Christophe Leroy, split out test and dynamically free pages.

v6: Guard freeing page properly. Drop WARN_ON_ONCE(pte_none(*ptep)),
     on reflection it's unnecessary debugging cruft with too high a
     false positive rate.

v7: tlb flush, thanks Mark.
    explain more clearly how freeing works and is concurrency-safe.
---
 Documentation/dev-tools/kasan.rst |  63 +++++++++
 include/linux/kasan.h             |  31 +++++
 include/linux/moduleloader.h      |   2 +-
 include/linux/vmalloc.h           |  12 ++
 lib/Kconfig.kasan                 |  16 +++
 mm/kasan/common.c                 | 204 ++++++++++++++++++++++++++++++
 mm/kasan/generic_report.c         |   3 +
 mm/kasan/kasan.h                  |   1 +
 mm/vmalloc.c                      |  45 ++++++-
 9 files changed, 375 insertions(+), 2 deletions(-)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index b72d07d70239..bdb92c3de7a5 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -215,3 +215,66 @@ brk handler is used to print bug reports.
 A potential expansion of this mode is a hardware tag-based mode, which would
 use hardware memory tagging support instead of compiler instrumentation and
 manual shadow memory manipulation.
+
+What memory accesses are sanitised by KASAN?
+--------------------------------------------
+
+The kernel maps memory in a number of different parts of the address
+space. This poses something of a problem for KASAN, which requires
+that all addresses accessed by instrumented code have a valid shadow
+region.
+
+The range of kernel virtual addresses is large: there is not enough
+real memory to support a real shadow region for every address that
+could be accessed by the kernel.
+
+By default
+~~~~~~~~~~
+
+By default, architectures only map real memory over the shadow region
+for the linear mapping (and potentially other small areas). For all
+other areas - such as vmalloc and vmemmap space - a single read-only
+page is mapped over the shadow area. This read-only shadow page
+declares all memory accesses as permitted.
+
+This presents a problem for modules: they do not live in the linear
+mapping, but in a dedicated module space. By hooking in to the module
+allocator, KASAN can temporarily map real shadow memory to cover
+them. This allows detection of invalid accesses to module globals, for
+example.
+
+This also creates an incompatibility with ``VMAP_STACK``: if the stack
+lives in vmalloc space, it will be shadowed by the read-only page, and
+the kernel will fault when trying to set up the shadow data for stack
+variables.
+
+CONFIG_KASAN_VMALLOC
+~~~~~~~~~~~~~~~~~~~~
+
+With ``CONFIG_KASAN_VMALLOC``, KASAN can cover vmalloc space at the
+cost of greater memory usage. Currently this is only supported on x86.
+
+This works by hooking into vmalloc and vmap, and dynamically
+allocating real shadow memory to back the mappings.
+
+Most mappings in vmalloc space are small, requiring less than a full
+page of shadow space. Allocating a full shadow page per mapping would
+therefore be wasteful. Furthermore, to ensure that different mappings
+use different shadow pages, mappings would have to be aligned to
+``KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE``.
+
+Instead, we share backing space across multiple mappings. We allocate
+a backing page when a mapping in vmalloc space uses a particular page
+of the shadow region. This page can be shared by other vmalloc
+mappings later on.
+
+We hook in to the vmap infrastructure to lazily clean up unused shadow
+memory.
+
+To avoid the difficulties around swapping mappings around, we expect
+that the part of the shadow region that covers the vmalloc space will
+not be covered by the early shadow page, but will be left
+unmapped. This will require changes in arch-specific code.
+
+This allows ``VMAP_STACK`` support on x86, and can simplify support of
+architectures that do not have a fixed module region.
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index cc8a03cc9674..4f404c565db1 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -70,8 +70,18 @@ struct kasan_cache {
 	int free_meta_offset;
 };
 
+/*
+ * These functions provide a special case to support backing module
+ * allocations with real shadow memory. With KASAN vmalloc, the special
+ * case is unnecessary, as the work is handled in the generic case.
+ */
+#ifndef CONFIG_KASAN_VMALLOC
 int kasan_module_alloc(void *addr, size_t size);
 void kasan_free_shadow(const struct vm_struct *vm);
+#else
+static inline int kasan_module_alloc(void *addr, size_t size) { return 0; }
+static inline void kasan_free_shadow(const struct vm_struct *vm) {}
+#endif
 
 int kasan_add_zero_shadow(void *start, unsigned long size);
 void kasan_remove_zero_shadow(void *start, unsigned long size);
@@ -194,4 +204,25 @@ static inline void *kasan_reset_tag(const void *addr)
 
 #endif /* CONFIG_KASAN_SW_TAGS */
 
+#ifdef CONFIG_KASAN_VMALLOC
+int kasan_populate_vmalloc(unsigned long requested_size,
+			   struct vm_struct *area);
+void kasan_poison_vmalloc(void *start, unsigned long size);
+void kasan_release_vmalloc(unsigned long start, unsigned long end,
+			   unsigned long free_region_start,
+			   unsigned long free_region_end);
+#else
+static inline int kasan_populate_vmalloc(unsigned long requested_size,
+					 struct vm_struct *area)
+{
+	return 0;
+}
+
+static inline void kasan_poison_vmalloc(void *start, unsigned long size) {}
+static inline void kasan_release_vmalloc(unsigned long start,
+					 unsigned long end,
+					 unsigned long free_region_start,
+					 unsigned long free_region_end) {}
+#endif
+
 #endif /* LINUX_KASAN_H */
diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
index 5229c18025e9..ca92aea8a6bd 100644
--- a/include/linux/moduleloader.h
+++ b/include/linux/moduleloader.h
@@ -91,7 +91,7 @@ void module_arch_cleanup(struct module *mod);
 /* Any cleanup before freeing mod->module_init */
 void module_arch_freeing_init(struct module *mod);
 
-#ifdef CONFIG_KASAN
+#if defined(CONFIG_KASAN) && !defined(CONFIG_KASAN_VMALLOC)
 #include <linux/kasan.h>
 #define MODULE_ALIGN (PAGE_SIZE << KASAN_SHADOW_SCALE_SHIFT)
 #else
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index a1334bd18ef1..01bd08f0f52f 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -21,6 +21,18 @@ struct notifier_block;		/* in notifier.h */
 #define VM_UNINITIALIZED	0x00000020	/* vm_struct is not fully initialized */
 #define VM_NO_GUARD		0x00000040      /* don't add guard page */
 #define VM_KASAN		0x00000080      /* has allocated kasan shadow memory */
+
+/*
+ * VM_KASAN is used slighly differently depending on CONFIG_KASAN_VMALLOC.
+ *
+ * If IS_ENABLED(CONFIG_KASAN_VMALLOC), VM_KASAN is set on a vm_struct after
+ * shadow memory has been mapped. It's used to handle allocation errors so that
+ * we don't try to poision shadow on free if it was never allocated.
+ *
+ * Otherwise, VM_KASAN is set for kasan_module_alloc() allocations and used to
+ * determine which allocations need the module shadow freed.
+ */
+
 /*
  * Memory with VM_FLUSH_RESET_PERMS cannot be freed in an interrupt or with
  * vfree_atomic().
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 6c9682ce0254..81f5464ea9e1 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -6,6 +6,9 @@ config HAVE_ARCH_KASAN
 config HAVE_ARCH_KASAN_SW_TAGS
 	bool
 
+config	HAVE_ARCH_KASAN_VMALLOC
+	bool
+
 config CC_HAS_KASAN_GENERIC
 	def_bool $(cc-option, -fsanitize=kernel-address)
 
@@ -142,6 +145,19 @@ config KASAN_SW_TAGS_IDENTIFY
 	  (use-after-free or out-of-bounds) at the cost of increased
 	  memory consumption.
 
+config KASAN_VMALLOC
+	bool "Back mappings in vmalloc space with real shadow memory"
+	depends on KASAN && HAVE_ARCH_KASAN_VMALLOC
+	help
+	  By default, the shadow region for vmalloc space is the read-only
+	  zero page. This means that KASAN cannot detect errors involving
+	  vmalloc space.
+
+	  Enabling this option will hook in to vmap/vmalloc and back those
+	  mappings with real shadow memory allocated on demand. This allows
+	  for KASAN to detect more sorts of errors (and to support vmapped
+	  stacks), but at the cost of higher memory usage.
+
 config TEST_KASAN
 	tristate "Module for testing KASAN for bug detection"
 	depends on m && KASAN
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 6814d6d6a023..e33cbab83309 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -36,6 +36,8 @@
 #include <linux/bug.h>
 #include <linux/uaccess.h>
 
+#include <asm/tlbflush.h>
+
 #include "kasan.h"
 #include "../slab.h"
 
@@ -590,6 +592,7 @@ void kasan_kfree_large(void *ptr, unsigned long ip)
 	/* The object will be poisoned by page_alloc. */
 }
 
+#ifndef CONFIG_KASAN_VMALLOC
 int kasan_module_alloc(void *addr, size_t size)
 {
 	void *ret;
@@ -625,6 +628,7 @@ void kasan_free_shadow(const struct vm_struct *vm)
 	if (vm->flags & VM_KASAN)
 		vfree(kasan_mem_to_shadow(vm->addr));
 }
+#endif
 
 extern void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip);
 
@@ -744,3 +748,203 @@ static int __init kasan_memhotplug_init(void)
 
 core_initcall(kasan_memhotplug_init);
 #endif
+
+#ifdef CONFIG_KASAN_VMALLOC
+static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
+				      void *unused)
+{
+	unsigned long page;
+	pte_t pte;
+
+	if (likely(!pte_none(*ptep)))
+		return 0;
+
+	page = __get_free_page(GFP_KERNEL);
+	if (!page)
+		return -ENOMEM;
+
+	memset((void *)page, KASAN_VMALLOC_INVALID, PAGE_SIZE);
+	pte = pfn_pte(PFN_DOWN(__pa(page)), PAGE_KERNEL);
+
+	/*
+	 * Ensure poisoning is visible before the shadow is made visible
+	 * to other CPUs.
+	 */
+	smp_wmb();
+
+	spin_lock(&init_mm.page_table_lock);
+	if (likely(pte_none(*ptep))) {
+		set_pte_at(&init_mm, addr, ptep, pte);
+		page = 0;
+	}
+	spin_unlock(&init_mm.page_table_lock);
+	if (page)
+		free_page(page);
+	return 0;
+}
+
+int kasan_populate_vmalloc(unsigned long requested_size, struct vm_struct *area)
+{
+	unsigned long shadow_start, shadow_end;
+	int ret;
+
+	shadow_start = (unsigned long)kasan_mem_to_shadow(area->addr);
+	shadow_start = ALIGN_DOWN(shadow_start, PAGE_SIZE);
+	shadow_end = (unsigned long)kasan_mem_to_shadow(area->addr +
+							area->size);
+	shadow_end = ALIGN(shadow_end, PAGE_SIZE);
+
+	ret = apply_to_page_range(&init_mm, shadow_start,
+				  shadow_end - shadow_start,
+				  kasan_populate_vmalloc_pte, NULL);
+	if (ret)
+		return ret;
+
+	kasan_unpoison_shadow(area->addr, requested_size);
+
+	area->flags |= VM_KASAN;
+
+	return 0;
+}
+
+/*
+ * Poison the shadow for a vmalloc region. Called as part of the
+ * freeing process at the time the region is freed.
+ */
+void kasan_poison_vmalloc(void *start, unsigned long size)
+{
+	size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
+	kasan_poison_shadow(start, size, KASAN_VMALLOC_INVALID);
+}
+
+static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
+					void *unused)
+{
+	unsigned long page;
+
+	page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT);
+
+	spin_lock(&init_mm.page_table_lock);
+
+	if (likely(!pte_none(*ptep))) {
+		pte_clear(&init_mm, addr, ptep);
+		free_page(page);
+	}
+	spin_unlock(&init_mm.page_table_lock);
+
+	return 0;
+}
+
+/*
+ * Release the backing for the vmalloc region [start, end), which
+ * lies within the free region [free_region_start, free_region_end).
+ *
+ * This can be run lazily, long after the region was freed. It runs
+ * under vmap_area_lock, so it's not safe to interact with the vmalloc/vmap
+ * infrastructure.
+ *
+ * How does this work?
+ * -------------------
+ *
+ * We have a region that is page aligned, labelled as A.
+ * That might not map onto the shadow in a way that is page-aligned:
+ *
+ *                    start                     end
+ *                    v                         v
+ * |????????|????????|AAAAAAAA|AA....AA|AAAAAAAA|????????| < vmalloc
+ *  -------- -------- --------          -------- --------
+ *      |        |       |                 |        |
+ *      |        |       |         /-------/        |
+ *      \-------\|/------/         |/---------------/
+ *              |||                ||
+ *             |??AAAAAA|AAAAAAAA|AA??????|                < shadow
+ *                 (1)      (2)      (3)
+ *
+ * First we align the start upwards and the end downwards, so that the
+ * shadow of the region aligns with shadow page boundaries. In the
+ * example, this gives us the shadow page (2). This is the shadow entirely
+ * covered by this allocation.
+ *
+ * Then we have the tricky bits. We want to know if we can free the
+ * partially covered shadow pages - (1) and (3) in the example. For this,
+ * we are given the start and end of the free region that contains this
+ * allocation. Extending our previous example, we could have:
+ *
+ *  free_region_start                                    free_region_end
+ *  |                 start                     end      |
+ *  v                 v                         v        v
+ * |FFFFFFFF|FFFFFFFF|AAAAAAAA|AA....AA|AAAAAAAA|FFFFFFFF| < vmalloc
+ *  -------- -------- --------          -------- --------
+ *      |        |       |                 |        |
+ *      |        |       |         /-------/        |
+ *      \-------\|/------/         |/---------------/
+ *              |||                ||
+ *             |FFAAAAAA|AAAAAAAA|AAF?????|                < shadow
+ *                 (1)      (2)      (3) 
+ *
+ * Once again, we align the start of the free region up, and the end of
+ * the free region down so that the shadow is page aligned. So we can free
+ * page (1) - we know no allocation currently uses anything in that page,
+ * because all of it is in the vmalloc free region. But we cannot free
+ * page (3), because we can't be sure that the rest of it is unused.
+ *
+ * We only consider pages that contain part of the original region for
+ * freeing: we don't try to free other pages from the free region or we'd
+ * end up trying to free huge chunks of virtual address space.
+ *
+ * Concurrency
+ * -----------
+ *
+ * How do we know that we're not freeing a page that is simultaneously
+ * being used for a fresh allocation in kasan_populate_vmalloc(_pte)?
+ *
+ * We _can_ have kasan_release_vmalloc and kasan_populate_vmalloc running
+ * at the same time. While we run under vmap_area_lock, the population
+ * code does not: alloc_vmap_area and the per-cpu allocator both take the
+ * lock before calling __alloc_vmap_area to identify and reserve a region,
+ * and both release the lock before we call kasan_populate_vmalloc.
+ *
+ * vmap_area_lock instead operates to ensure that the larger range
+ * [free_region_start, free_region_end) is safe: because __alloc_vmap_area
+ * is excluded, no space identified as free will become non-free while we
+ * are running. This means that so long as we are careful with alignment
+ * and only free shadow pages entirely covered by the free region, we will
+ * not run in to trouble - any simultaneous allocations will be for
+ * disjoint regions.
+ */
+void kasan_release_vmalloc(unsigned long start, unsigned long end,
+			   unsigned long free_region_start,
+			   unsigned long free_region_end)
+{
+	void *shadow_start, *shadow_end;
+	unsigned long region_start, region_end;
+
+	region_start = ALIGN(start, PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
+	region_end = ALIGN_DOWN(end, PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
+
+	free_region_start = ALIGN(free_region_start,
+				  PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
+
+	if (start != region_start &&
+	    free_region_start < region_start)
+		region_start -= PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE;
+
+	free_region_end = ALIGN_DOWN(free_region_end,
+				     PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
+
+	if (end != region_end &&
+	    free_region_end > region_end)
+		region_end += PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE;
+
+	shadow_start = kasan_mem_to_shadow((void *)region_start);
+	shadow_end = kasan_mem_to_shadow((void *)region_end);
+
+	if (shadow_end > shadow_start) {
+		apply_to_page_range(&init_mm, (unsigned long)shadow_start,
+				    (unsigned long)(shadow_end - shadow_start),
+				    kasan_depopulate_vmalloc_pte, NULL);
+		flush_tlb_kernel_range((unsigned long)shadow_start,
+				       (unsigned long)shadow_end);
+	}
+}
+#endif
diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
index 36c645939bc9..2d97efd4954f 100644
--- a/mm/kasan/generic_report.c
+++ b/mm/kasan/generic_report.c
@@ -86,6 +86,9 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info)
 	case KASAN_ALLOCA_RIGHT:
 		bug_type = "alloca-out-of-bounds";
 		break;
+	case KASAN_VMALLOC_INVALID:
+		bug_type = "vmalloc-out-of-bounds";
+		break;
 	}
 
 	return bug_type;
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 35cff6bbb716..3a083274628e 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -25,6 +25,7 @@
 #endif
 
 #define KASAN_GLOBAL_REDZONE    0xFA  /* redzone for global variable */
+#define KASAN_VMALLOC_INVALID   0xF9  /* unallocated space in vmapped page */
 
 /*
  * Stack redzone shadow values
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index b8101030f79e..bf806566cad0 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -690,8 +690,19 @@ merge_or_add_vmap_area(struct vmap_area *va,
 	struct list_head *next;
 	struct rb_node **link;
 	struct rb_node *parent;
+	unsigned long orig_start, orig_end;
 	bool merged = false;
 
+	/*
+	 * To manage KASAN vmalloc memory usage, we use this opportunity to
+	 * clean up the shadow memory allocated to back this allocation.
+	 * Because a vmalloc shadow page covers several pages, the start or end
+	 * of an allocation might not align with a shadow page. Use the merging
+	 * opportunities to try to extend the region we can release.
+	 */
+	orig_start = va->va_start;
+	orig_end = va->va_end;
+
 	/*
 	 * Find a place in the tree where VA potentially will be
 	 * inserted, unless it is merged with its sibling/siblings.
@@ -741,6 +752,10 @@ merge_or_add_vmap_area(struct vmap_area *va,
 		if (sibling->va_end == va->va_start) {
 			sibling->va_end = va->va_end;
 
+			kasan_release_vmalloc(orig_start, orig_end,
+					      sibling->va_start,
+					      sibling->va_end);
+
 			/* Check and update the tree if needed. */
 			augment_tree_propagate_from(sibling);
 
@@ -754,6 +769,8 @@ merge_or_add_vmap_area(struct vmap_area *va,
 	}
 
 insert:
+	kasan_release_vmalloc(orig_start, orig_end, va->va_start, va->va_end);
+
 	if (!merged) {
 		link_va(va, root, parent, link, head);
 		augment_tree_propagate_from(va);
@@ -2068,6 +2085,22 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
 
 	setup_vmalloc_vm(area, va, flags, caller);
 
+	/*
+	 * For KASAN, if we are in vmalloc space, we need to cover the shadow
+	 * area with real memory. If we come here through VM_ALLOC, this is
+	 * done by a higher level function that has access to the true size,
+	 * which might not be a full page.
+	 *
+	 * We assume module space comes via VM_ALLOC path.
+	 */
+	if (is_vmalloc_addr(area->addr) && !(area->flags & VM_ALLOC)) {
+		if (kasan_populate_vmalloc(area->size, area)) {
+			unmap_vmap_area(va);
+			kfree(area);
+			return NULL;
+		}
+	}
+
 	return area;
 }
 
@@ -2245,6 +2278,9 @@ static void __vunmap(const void *addr, int deallocate_pages)
 	debug_check_no_locks_freed(area->addr, get_vm_area_size(area));
 	debug_check_no_obj_freed(area->addr, get_vm_area_size(area));
 
+	if (area->flags & VM_KASAN)
+		kasan_poison_vmalloc(area->addr, area->size);
+
 	vm_remove_mappings(area, deallocate_pages);
 
 	if (deallocate_pages) {
@@ -2495,6 +2531,9 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	if (!addr)
 		return NULL;
 
+	if (kasan_populate_vmalloc(real_size, area))
+		return NULL;
+
 	/*
 	 * In this function, newly allocated vm_struct has VM_UNINITIALIZED
 	 * flag. It means that vm_struct is not fully initialized.
@@ -3349,10 +3388,14 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 	spin_unlock(&vmap_area_lock);
 
 	/* insert all vm's */
-	for (area = 0; area < nr_vms; area++)
+	for (area = 0; area < nr_vms; area++) {
 		setup_vmalloc_vm(vms[area], vas[area], VM_ALLOC,
 				 pcpu_get_vm_areas);
 
+		/* assume success here */
+		kasan_populate_vmalloc(sizes[area], vms[area]);
+	}
+
 	kfree(vas);
 	return vms;
 
-- 
2.20.1

[PATCH v7 2/5] kasan: add test for vmalloc

[Daniel Axtens]

Test kasan vmalloc support by adding a new test to the module.

Signed-off-by: Daniel Axtens <dja@axtens.net>

--

v5: split out per Christophe Leroy
---
 lib/test_kasan.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 49cc4d570a40..328d33beae36 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -19,6 +19,7 @@
 #include <linux/string.h>
 #include <linux/uaccess.h>
 #include <linux/io.h>
+#include <linux/vmalloc.h>
 
 #include <asm/page.h>
 
@@ -748,6 +749,30 @@ static noinline void __init kmalloc_double_kzfree(void)
 	kzfree(ptr);
 }
 
+#ifdef CONFIG_KASAN_VMALLOC
+static noinline void __init vmalloc_oob(void)
+{
+	void *area;
+
+	pr_info("vmalloc out-of-bounds\n");
+
+	/*
+	 * We have to be careful not to hit the guard page.
+	 * The MMU will catch that and crash us.
+	 */
+	area = vmalloc(3000);
+	if (!area) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	((volatile char *)area)[3100];
+	vfree(area);
+}
+#else
+static void __init vmalloc_oob(void) {}
+#endif
+
 static int __init kmalloc_tests_init(void)
 {
 	/*
@@ -793,6 +818,7 @@ static int __init kmalloc_tests_init(void)
 	kasan_strings();
 	kasan_bitops();
 	kmalloc_double_kzfree();
+	vmalloc_oob();
 
 	kasan_restore_multi_shot(multishot);
 
-- 
2.20.1

[PATCH v7 3/5] fork: support VMAP_STACK with KASAN_VMALLOC

[Daniel Axtens]

Supporting VMAP_STACK with KASAN_VMALLOC is straightforward:

 - clear the shadow region of vmapped stacks when swapping them in
 - tweak Kconfig to allow VMAP_STACK to be turned on with KASAN

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 arch/Kconfig  | 9 +++++----
 kernel/fork.c | 4 ++++
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 6728c5fa057e..e15f1486682a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -843,16 +843,17 @@ config HAVE_ARCH_VMAP_STACK
 config VMAP_STACK
 	default y
 	bool "Use a virtually-mapped stack"
-	depends on HAVE_ARCH_VMAP_STACK && !KASAN
+	depends on HAVE_ARCH_VMAP_STACK
+	depends on !KASAN || KASAN_VMALLOC
 	---help---
 	  Enable this if you want the use virtually-mapped kernel stacks
 	  with guard pages.  This causes kernel stack overflows to be
 	  caught immediately rather than causing difficult-to-diagnose
 	  corruption.
 
-	  This is presently incompatible with KASAN because KASAN expects
-	  the stack to map directly to the KASAN shadow map using a formula
-	  that is incorrect if the stack is in vmalloc space.
+	  To use this with KASAN, the architecture must support backing
+	  virtual mappings with real shadow memory, and KASAN_VMALLOC must
+	  be enabled.
 
 config ARCH_OPTIONAL_KERNEL_RWX
 	def_bool n
diff --git a/kernel/fork.c b/kernel/fork.c
index f601168f6b21..52279fd5e72d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -94,6 +94,7 @@
 #include <linux/livepatch.h>
 #include <linux/thread_info.h>
 #include <linux/stackleak.h>
+#include <linux/kasan.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -229,6 +230,9 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 		if (!s)
 			continue;
 
+		/* Clear the KASAN shadow of the stack. */
+		kasan_unpoison_shadow(s->addr, THREAD_SIZE);
+
 		/* Clear stale pointers from reused stack. */
 		memset(s->addr, 0, THREAD_SIZE);
 
-- 
2.20.1

[PATCH v7 4/5] x86/kasan: support KASAN_VMALLOC

[Daniel Axtens]

In the case where KASAN directly allocates memory to back vmalloc
space, don't map the early shadow page over it.

We prepopulate pgds/p4ds for the range that would otherwise be empty.
This is required to get it synced to hardware on boot, allowing the
lower levels of the page tables to be filled dynamically.

Acked-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>

---
v5: fix some checkpatch CHECK warnings. There are some that remain
    around lines ending with '(': I have not changed these because
    it's consistent with the rest of the file and it's not easy to
    see how to fix it without creating an overlong line or lots of
    temporary variables.

v2: move from faulting in shadow pgds to prepopulating
---
 arch/x86/Kconfig            |  1 +
 arch/x86/mm/kasan_init_64.c | 60 +++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2502f7f60c9c..300b4766ccfa 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -134,6 +134,7 @@ config X86
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_KASAN			if X86_64
+	select HAVE_ARCH_KASAN_VMALLOC		if X86_64
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS		if MMU
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if MMU && COMPAT
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 296da58f3013..8f00f462709e 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -245,6 +245,51 @@ static void __init kasan_map_early_shadow(pgd_t *pgd)
 	} while (pgd++, addr = next, addr != end);
 }
 
+static void __init kasan_shallow_populate_p4ds(pgd_t *pgd,
+					       unsigned long addr,
+					       unsigned long end,
+					       int nid)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	void *p;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+
+		if (p4d_none(*p4d)) {
+			p = early_alloc(PAGE_SIZE, nid, true);
+			p4d_populate(&init_mm, p4d, p);
+		}
+	} while (p4d++, addr = next, addr != end);
+}
+
+static void __init kasan_shallow_populate_pgds(void *start, void *end)
+{
+	unsigned long addr, next;
+	pgd_t *pgd;
+	void *p;
+	int nid = early_pfn_to_nid((unsigned long)start);
+
+	addr = (unsigned long)start;
+	pgd = pgd_offset_k(addr);
+	do {
+		next = pgd_addr_end(addr, (unsigned long)end);
+
+		if (pgd_none(*pgd)) {
+			p = early_alloc(PAGE_SIZE, nid, true);
+			pgd_populate(&init_mm, pgd, p);
+		}
+
+		/*
+		 * we need to populate p4ds to be synced when running in
+		 * four level mode - see sync_global_pgds_l4()
+		 */
+		kasan_shallow_populate_p4ds(pgd, addr, next, nid);
+	} while (pgd++, addr = next, addr != (unsigned long)end);
+}
+
 #ifdef CONFIG_KASAN_INLINE
 static int kasan_die_handler(struct notifier_block *self,
 			     unsigned long val,
@@ -352,9 +397,24 @@ void __init kasan_init(void)
 	shadow_cpu_entry_end = (void *)round_up(
 			(unsigned long)shadow_cpu_entry_end, PAGE_SIZE);
 
+	/*
+	 * If we're in full vmalloc mode, don't back vmalloc space with early
+	 * shadow pages. Instead, prepopulate pgds/p4ds so they are synced to
+	 * the global table and we can populate the lower levels on demand.
+	 */
+#ifdef CONFIG_KASAN_VMALLOC
+	kasan_shallow_populate_pgds(
+		kasan_mem_to_shadow((void *)PAGE_OFFSET + MAXMEM),
+		kasan_mem_to_shadow((void *)VMALLOC_END));
+
+	kasan_populate_early_shadow(
+		kasan_mem_to_shadow((void *)VMALLOC_END + 1),
+		shadow_cpu_entry_begin);
+#else
 	kasan_populate_early_shadow(
 		kasan_mem_to_shadow((void *)PAGE_OFFSET + MAXMEM),
 		shadow_cpu_entry_begin);
+#endif
 
 	kasan_populate_shadow((unsigned long)shadow_cpu_entry_begin,
 			      (unsigned long)shadow_cpu_entry_end, 0);
-- 
2.20.1

[PATCH v7 5/5] kasan debug: track pages allocated for vmalloc shadow

[Daniel Axtens]

Provide the current number of vmalloc shadow pages in
/sys/kernel/debug/kasan_vmalloc/shadow_pages.

Signed-off-by: Daniel Axtens <dja@axtens.net>

---

Merging this is probably overkill, but I leave it to the discretion
of the broader community.

On v4 (no dynamic freeing), I saw the following approximate figures
on my test VM:

 - fresh boot: 720
 - after test_vmalloc: ~14000

With v5 (lazy dynamic freeing):

 - boot: ~490-500
 - running modprobe test_vmalloc pushes the figures up to sometimes
    as high as ~14000, but they drop down to ~560 after the test ends.
    I'm not sure where the extra sixty pages are from, but running the
    test repeately doesn't cause the number to keep growing, so I don't
    think we're leaking.
 - with vmap_stack, spawning tasks pushes the figure up to ~4200, then
    some clearing kicks in and drops it down to previous levels again.
---
 mm/kasan/common.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index e33cbab83309..e40854512417 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -35,6 +35,7 @@
 #include <linux/vmalloc.h>
 #include <linux/bug.h>
 #include <linux/uaccess.h>
+#include <linux/debugfs.h>
 
 #include <asm/tlbflush.h>
 
@@ -750,6 +751,8 @@ core_initcall(kasan_memhotplug_init);
 #endif
 
 #ifdef CONFIG_KASAN_VMALLOC
+static u64 vmalloc_shadow_pages;
+
 static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 				      void *unused)
 {
@@ -776,6 +779,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 	if (likely(pte_none(*ptep))) {
 		set_pte_at(&init_mm, addr, ptep, pte);
 		page = 0;
+		vmalloc_shadow_pages++;
 	}
 	spin_unlock(&init_mm.page_table_lock);
 	if (page)
@@ -829,6 +833,7 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 	if (likely(!pte_none(*ptep))) {
 		pte_clear(&init_mm, addr, ptep);
 		free_page(page);
+		vmalloc_shadow_pages--;
 	}
 	spin_unlock(&init_mm.page_table_lock);
 
@@ -947,4 +952,25 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
 				       (unsigned long)shadow_end);
 	}
 }
+
+static __init int kasan_init_vmalloc_debugfs(void)
+{
+	struct dentry *root, *count;
+
+	root = debugfs_create_dir("kasan_vmalloc", NULL);
+	if (IS_ERR(root)) {
+		if (PTR_ERR(root) == -ENODEV)
+			return 0;
+		return PTR_ERR(root);
+	}
+
+	count = debugfs_create_u64("shadow_pages", 0444, root,
+				   &vmalloc_shadow_pages);
+
+	if (IS_ERR(count))
+		return PTR_ERR(root);
+
+	return 0;
+}
+late_initcall(kasan_init_vmalloc_debugfs);
 #endif
-- 
2.20.1

Re: [PATCH v7 5/5] kasan debug: track pages allocated for vmalloc shadow

[Andrey Konovalov]

On Tue, Sep 3, 2019 at 4:56 PM Daniel Axtens <dja@axtens.net> wrote:
>
> Provide the current number of vmalloc shadow pages in
> /sys/kernel/debug/kasan_vmalloc/shadow_pages.

Maybe it makes sense to put this into /sys/kernel/debug/kasan/
(without _vmalloc) and name e.g. vmalloc_shadow_pages? In case we want
to expose more generic KASAN debugging info later.

>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
>
> ---
>
> Merging this is probably overkill, but I leave it to the discretion
> of the broader community.
>
> On v4 (no dynamic freeing), I saw the following approximate figures
> on my test VM:
>
>  - fresh boot: 720
>  - after test_vmalloc: ~14000
>
> With v5 (lazy dynamic freeing):
>
>  - boot: ~490-500
>  - running modprobe test_vmalloc pushes the figures up to sometimes
>     as high as ~14000, but they drop down to ~560 after the test ends.
>     I'm not sure where the extra sixty pages are from, but running the
>     test repeately doesn't cause the number to keep growing, so I don't
>     think we're leaking.
>  - with vmap_stack, spawning tasks pushes the figure up to ~4200, then
>     some clearing kicks in and drops it down to previous levels again.
> ---
>  mm/kasan/common.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index e33cbab83309..e40854512417 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -35,6 +35,7 @@
>  #include <linux/vmalloc.h>
>  #include <linux/bug.h>
>  #include <linux/uaccess.h>
> +#include <linux/debugfs.h>
>
>  #include <asm/tlbflush.h>
>
> @@ -750,6 +751,8 @@ core_initcall(kasan_memhotplug_init);
>  #endif
>
>  #ifdef CONFIG_KASAN_VMALLOC
> +static u64 vmalloc_shadow_pages;
> +
>  static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>                                       void *unused)
>  {
> @@ -776,6 +779,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>         if (likely(pte_none(*ptep))) {
>                 set_pte_at(&init_mm, addr, ptep, pte);
>                 page = 0;
> +               vmalloc_shadow_pages++;
>         }
>         spin_unlock(&init_mm.page_table_lock);
>         if (page)
> @@ -829,6 +833,7 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>         if (likely(!pte_none(*ptep))) {
>                 pte_clear(&init_mm, addr, ptep);
>                 free_page(page);
> +               vmalloc_shadow_pages--;
>         }
>         spin_unlock(&init_mm.page_table_lock);
>
> @@ -947,4 +952,25 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
>                                        (unsigned long)shadow_end);
>         }
>  }
> +
> +static __init int kasan_init_vmalloc_debugfs(void)
> +{
> +       struct dentry *root, *count;
> +
> +       root = debugfs_create_dir("kasan_vmalloc", NULL);
> +       if (IS_ERR(root)) {
> +               if (PTR_ERR(root) == -ENODEV)
> +                       return 0;
> +               return PTR_ERR(root);
> +       }
> +
> +       count = debugfs_create_u64("shadow_pages", 0444, root,
> +                                  &vmalloc_shadow_pages);
> +
> +       if (IS_ERR(count))
> +               return PTR_ERR(root);
> +
> +       return 0;
> +}
> +late_initcall(kasan_init_vmalloc_debugfs);
>  #endif
> --
> 2.20.1
>
> --
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> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com.
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Re: [PATCH v7 5/5] kasan debug: track pages allocated for vmalloc shadow

[Daniel Axtens]

Andrey Konovalov <andreyknvl@google.com> writes:

> On Tue, Sep 3, 2019 at 4:56 PM Daniel Axtens <dja@axtens.net> wrote:
>>
>> Provide the current number of vmalloc shadow pages in
>> /sys/kernel/debug/kasan_vmalloc/shadow_pages.
>
> Maybe it makes sense to put this into /sys/kernel/debug/kasan/
> (without _vmalloc) and name e.g. vmalloc_shadow_pages? In case we want
> to expose more generic KASAN debugging info later.

We certainly could. I just wonder if this patch is useful on an ongoing
basis. I wrote it to validate my work on lazy freeing of shadow pages -
which is why I included it - but I'm not sure it has much ongoing value
beyond demonstrating that the freeing code works.

If we think it's worth holding on to this patch, I can certainly adjust
the paths.

Regards,
Daniel

>
>>
>> Signed-off-by: Daniel Axtens <dja@axtens.net>
>>
>> ---
>>
>> Merging this is probably overkill, but I leave it to the discretion
>> of the broader community.
>>
>> On v4 (no dynamic freeing), I saw the following approximate figures
>> on my test VM:
>>
>>  - fresh boot: 720
>>  - after test_vmalloc: ~14000
>>
>> With v5 (lazy dynamic freeing):
>>
>>  - boot: ~490-500
>>  - running modprobe test_vmalloc pushes the figures up to sometimes
>>     as high as ~14000, but they drop down to ~560 after the test ends.
>>     I'm not sure where the extra sixty pages are from, but running the
>>     test repeately doesn't cause the number to keep growing, so I don't
>>     think we're leaking.
>>  - with vmap_stack, spawning tasks pushes the figure up to ~4200, then
>>     some clearing kicks in and drops it down to previous levels again.
>> ---
>>  mm/kasan/common.c | 26 ++++++++++++++++++++++++++
>>  1 file changed, 26 insertions(+)
>>
>> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
>> index e33cbab83309..e40854512417 100644
>> --- a/mm/kasan/common.c
>> +++ b/mm/kasan/common.c
>> @@ -35,6 +35,7 @@
>>  #include <linux/vmalloc.h>
>>  #include <linux/bug.h>
>>  #include <linux/uaccess.h>
>> +#include <linux/debugfs.h>
>>
>>  #include <asm/tlbflush.h>
>>
>> @@ -750,6 +751,8 @@ core_initcall(kasan_memhotplug_init);
>>  #endif
>>
>>  #ifdef CONFIG_KASAN_VMALLOC
>> +static u64 vmalloc_shadow_pages;
>> +
>>  static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>>                                       void *unused)
>>  {
>> @@ -776,6 +779,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>>         if (likely(pte_none(*ptep))) {
>>                 set_pte_at(&init_mm, addr, ptep, pte);
>>                 page = 0;
>> +               vmalloc_shadow_pages++;
>>         }
>>         spin_unlock(&init_mm.page_table_lock);
>>         if (page)
>> @@ -829,6 +833,7 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>>         if (likely(!pte_none(*ptep))) {
>>                 pte_clear(&init_mm, addr, ptep);
>>                 free_page(page);
>> +               vmalloc_shadow_pages--;
>>         }
>>         spin_unlock(&init_mm.page_table_lock);
>>
>> @@ -947,4 +952,25 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
>>                                        (unsigned long)shadow_end);
>>         }
>>  }
>> +
>> +static __init int kasan_init_vmalloc_debugfs(void)
>> +{
>> +       struct dentry *root, *count;
>> +
>> +       root = debugfs_create_dir("kasan_vmalloc", NULL);
>> +       if (IS_ERR(root)) {
>> +               if (PTR_ERR(root) == -ENODEV)
>> +                       return 0;
>> +               return PTR_ERR(root);
>> +       }
>> +
>> +       count = debugfs_create_u64("shadow_pages", 0444, root,
>> +                                  &vmalloc_shadow_pages);
>> +
>> +       if (IS_ERR(count))
>> +               return PTR_ERR(root);
>> +
>> +       return 0;
>> +}
>> +late_initcall(kasan_init_vmalloc_debugfs);
>>  #endif
>> --
>> 2.20.1
>>
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Re: [PATCH v7 0/5] kasan: support backing vmalloc space with real shadow memory

[Christophe Leroy]

Hi Daniel,

Are any other patches required prior to this series ? I have tried to 
apply it on later powerpc/merge branch without success:


[root@localhost linux-powerpc]# git am 
/root/Downloads/kasan-support-backing-vmalloc-space-with-real-shadow-memory\(1\).patch 

Applying: kasan: support backing vmalloc space with real shadow memory
.git/rebase-apply/patch:389: trailing whitespace.
  *                 (1)      (2)      (3)
error: patch failed: lib/Kconfig.kasan:142
error: lib/Kconfig.kasan: patch does not apply
Patch failed at 0001 kasan: support backing vmalloc space with real 
shadow memory
The copy of the patch that failed is found in: .git/rebase-apply/patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".


[root@localhost linux-powerpc]# git am -3 
/root/Downloads/kasan-support-backing-vmalloc-space-with-real-shadow-memory\(1\).patch 

Applying: kasan: support backing vmalloc space with real shadow memory
error: sha1 information is lacking or useless (include/linux/vmalloc.h).
error: could not build fake ancestor
Patch failed at 0001 kasan: support backing vmalloc space with real 
shadow memory
The copy of the patch that failed is found in: .git/rebase-apply/patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".


Christophe

On 09/03/2019 02:55 PM, Daniel Axtens wrote:
> Currently, vmalloc space is backed by the early shadow page. This
> means that kasan is incompatible with VMAP_STACK.
> 
> This series provides a mechanism to back vmalloc space with real,
> dynamically allocated memory. I have only wired up x86, because that's
> the only currently supported arch I can work with easily, but it's
> very easy to wire up other architectures, and it appears that there is
> some work-in-progress code to do this on arm64 and s390.
> 
> This has been discussed before in the context of VMAP_STACK:
>   - https://bugzilla.kernel.org/show_bug.cgi?id=202009
>   - https://lkml.org/lkml/2018/7/22/198
>   - https://lkml.org/lkml/2019/7/19/822
> 
> In terms of implementation details:
> 
> Most mappings in vmalloc space are small, requiring less than a full
> page of shadow space. Allocating a full shadow page per mapping would
> therefore be wasteful. Furthermore, to ensure that different mappings
> use different shadow pages, mappings would have to be aligned to
> KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
> 
> Instead, share backing space across multiple mappings. Allocate a
> backing page when a mapping in vmalloc space uses a particular page of
> the shadow region. This page can be shared by other vmalloc mappings
> later on.
> 
> We hook in to the vmap infrastructure to lazily clean up unused shadow
> memory.
> 
> 
> v1: https://lore.kernel.org/linux-mm/20190725055503.19507-1-dja@axtens.net/
> v2: https://lore.kernel.org/linux-mm/20190729142108.23343-1-dja@axtens.net/
>   Address review comments:
>   - Patch 1: use kasan_unpoison_shadow's built-in handling of
>              ranges that do not align to a full shadow byte
>   - Patch 3: prepopulate pgds rather than faulting things in
> v3: https://lore.kernel.org/linux-mm/20190731071550.31814-1-dja@axtens.net/
>   Address comments from Mark Rutland:
>   - kasan_populate_vmalloc is a better name
>   - handle concurrency correctly
>   - various nits and cleanups
>   - relax module alignment in KASAN_VMALLOC case
> v4: https://lore.kernel.org/linux-mm/20190815001636.12235-1-dja@axtens.net/
>   Changes to patch 1 only:
>   - Integrate Mark's rework, thanks Mark!
>   - handle the case where kasan_populate_shadow might fail
>   - poision shadow on free, allowing the alloc path to just
>       unpoision memory that it uses
> v5: https://lore.kernel.org/linux-mm/20190830003821.10737-1-dja@axtens.net/
>   Address comments from Christophe Leroy:
>   - Fix some issues with my descriptions in commit messages and docs
>   - Dynamically free unused shadow pages by hooking into the vmap book-keeping
>   - Split out the test into a separate patch
>   - Optional patch to track the number of pages allocated
>   - minor checkpatch cleanups
> v6: https://lore.kernel.org/linux-mm/20190902112028.23773-1-dja@axtens.net/
>   Properly guard freeing pages in patch 1, drop debugging code.
> v7: Add a TLB flush on freeing, thanks Mark Rutland.
>      Explain more clearly how I think freeing is concurrency-safe.
> 
> Daniel Axtens (5):
>    kasan: support backing vmalloc space with real shadow memory
>    kasan: add test for vmalloc
>    fork: support VMAP_STACK with KASAN_VMALLOC
>    x86/kasan: support KASAN_VMALLOC
>    kasan debug: track pages allocated for vmalloc shadow
> 
>   Documentation/dev-tools/kasan.rst |  63 ++++++++
>   arch/Kconfig                      |   9 +-
>   arch/x86/Kconfig                  |   1 +
>   arch/x86/mm/kasan_init_64.c       |  60 ++++++++
>   include/linux/kasan.h             |  31 ++++
>   include/linux/moduleloader.h      |   2 +-
>   include/linux/vmalloc.h           |  12 ++
>   kernel/fork.c                     |   4 +
>   lib/Kconfig.kasan                 |  16 +++
>   lib/test_kasan.c                  |  26 ++++
>   mm/kasan/common.c                 | 230 ++++++++++++++++++++++++++++++
>   mm/kasan/generic_report.c         |   3 +
>   mm/kasan/kasan.h                  |   1 +
>   mm/vmalloc.c                      |  45 +++++-
>   14 files changed, 497 insertions(+), 6 deletions(-)
> 

Re: [PATCH v7 0/5] kasan: support backing vmalloc space with real shadow memory

[Daniel Axtens]

Hi Christophe,

> Are any other patches required prior to this series ? I have tried to 
> apply it on later powerpc/merge branch without success:

It applies on the latest linux-next. I didn't base it on powerpc/*
because it's generic.

Regards,
Daniel

Re: [PATCH v7 0/5] kasan: support backing vmalloc space with real shadow memory

[Christophe Leroy]

Le 11/09/2019 à 13:20, Daniel Axtens a écrit :
> Hi Christophe,
> 
>> Are any other patches required prior to this series ? I have tried to
>> apply it on later powerpc/merge branch without success:
> 
> It applies on the latest linux-next. I didn't base it on powerpc/*
> because it's generic.
> 

Ok, thanks.

I backported it to powerpc/merge and I'm testing it on PPC32 with 
VMAP_STACK.

Got a few challenges but it is working now.

Christophe