Re: [PATCH 1/4] kasan: allow arches to provide their own early shadow setup

[Christophe Leroy]

Le 07/08/2019 à 17:14, Christophe Leroy a écrit :


Le 07/08/2019 à 01:38, Daniel Axtens a écrit :
powerpc supports several different MMUs. In particular, book3s
machines support both a hash-table based MMU and a radix MMU.
These MMUs support different numbers of entries per directory
level: the PTES_PER_* defines evaluate to variables, not constants.
This leads to complier errors as global variables must have constant
sizes.

Allow architectures to manage their own early shadow variables so we
can work around this on powerpc.

This seems rather strange to move the early shadow tables out of 
mm/kasan/init.c allthough they are used there still.

What about doing for all what is already done for 
kasan_early_shadow_p4d[], in extenso define constant max sizes 
MAX_PTRS_PER_PTE, MAX_PTRS_PER_PMD and MAX_PTRS_PER_PUD ?

To illustrate my suggestion, see commit c65e774fb3f6af21 ("x86/mm: Make 
PGDIR_SHIFT and PTRS_PER_P4D variable")

The same principle should apply on all variable powerpc PTRS_PER_XXX.

Christophe


With a set of the following, it would remain transparent for other arches.
#ifndef MAX_PTRS_PER_PXX
#define MAX_PTRS_PER_PXX PTRS_PER_PXX
#endif

Then you would just need to do the following for Radix:

#define MAX_PTRS_PER_PTE        (1 << RADIX_PTE_INDEX_SIZE)
#define MAX_PTRS_PER_PMD        (1 << RADIX_PMD_INDEX_SIZE)
#define MAX_PTRS_PER_PUD        (1 << RADIX_PUD_INDEX_SIZE)


For the kasan_early_shadow_page[], I don't think we have variable 
PAGE_SIZE, have we ?

Christophe



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

---
Changes from RFC:

  - To make checkpatch happy, move ARCH_HAS_KASAN_EARLY_SHADOW from
    a random #define to a config option selected when building for
    ppc64 book3s
---
  include/linux/kasan.h |  2 ++
  lib/Kconfig.kasan     |  3 +++
  mm/kasan/init.c       | 10 ++++++++++
  3 files changed, 15 insertions(+)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index ec81113fcee4..15933da52a3e 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -14,11 +14,13 @@ struct task_struct;
  #include <asm/kasan.h>
  #include <asm/pgtable.h>
+#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
  extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
  extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
  extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
  extern pud_t kasan_early_shadow_pud[PTRS_PER_PUD];
  extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
+#endif
  int kasan_populate_early_shadow(const void *shadow_start,
                  const void *shadow_end);
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index a320dc2e9317..0621a0129c04 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -9,6 +9,9 @@ config HAVE_ARCH_KASAN_SW_TAGS
  config    HAVE_ARCH_KASAN_VMALLOC
      bool
+config ARCH_HAS_KASAN_EARLY_SHADOW
+    bool
+
  config CC_HAS_KASAN_GENERIC
      def_bool $(cc-option, -fsanitize=kernel-address)
diff --git a/mm/kasan/init.c b/mm/kasan/init.c
index ce45c491ebcd..7ef2b87a7988 100644
--- a/mm/kasan/init.c
+++ b/mm/kasan/init.c
@@ -31,10 +31,14 @@
   *   - Latter it reused it as zero shadow to cover large ranges of 
memory
   *     that allowed to access, but not handled by kasan 
(vmalloc/vmemmap ...).
   */
+#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
  unsigned char kasan_early_shadow_page[PAGE_SIZE] __page_aligned_bss;
+#endif
  #if CONFIG_PGTABLE_LEVELS > 4
+#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
  p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D] __page_aligned_bss;
+#endif
  static inline bool kasan_p4d_table(pgd_t pgd)
  {
      return pgd_page(pgd) == 
virt_to_page(lm_alias(kasan_early_shadow_p4d));
@@ -46,7 +50,9 @@ static inline bool kasan_p4d_table(pgd_t pgd)
  }
  #endif
  #if CONFIG_PGTABLE_LEVELS > 3
+#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
  pud_t kasan_early_shadow_pud[PTRS_PER_PUD] __page_aligned_bss;
+#endif
  static inline bool kasan_pud_table(p4d_t p4d)
  {
      return p4d_page(p4d) == 
virt_to_page(lm_alias(kasan_early_shadow_pud));
@@ -58,7 +64,9 @@ static inline bool kasan_pud_table(p4d_t p4d)
  }
  #endif
  #if CONFIG_PGTABLE_LEVELS > 2
+#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
  pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD] __page_aligned_bss;
+#endif
  static inline bool kasan_pmd_table(pud_t pud)
  {
      return pud_page(pud) == 
virt_to_page(lm_alias(kasan_early_shadow_pmd));
@@ -69,7 +77,9 @@ static inline bool kasan_pmd_table(pud_t pud)
      return false;
  }
  #endif
+#ifndef CONFIG_ARCH_HAS_KASAN_EARLY_SHADOW
  pte_t kasan_early_shadow_pte[PTRS_PER_PTE] __page_aligned_bss;
+#endif
  static inline bool kasan_pte_table(pmd_t pmd)
  {