Re: [PATCH v13 08/25] kasan: initialize shadow to 0xff for tag-based mode

[Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>]

On Thu, Dec 6, 2018 at 7:25 AM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:

A tag-based KASAN shadow memory cell contains a memory tag, that
corresponds to the tag in the top byte of the pointer, that points to that
memory. The native top byte value of kernel pointers is 0xff, so with
tag-based KASAN we need to initialize shadow memory to 0xff.

Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
 arch/arm64/mm/kasan_init.c | 15 +++++++++++++--
 include/linux/kasan.h      |  8 ++++++++

The version of this in  linux-next breaks arm64 allmodconfig for me:

mm/kasan/common.c: In function ‘kasan_module_alloc’:
mm/kasan/common.c:481:17: error: ‘KASAN_SHADOW_INIT’ undeclared (first use in this function)
   __memset(ret, KASAN_SHADOW_INIT, shadow_size);
                 ^
mm/kasan/common.c:481:17: note: each undeclared identifier is reported only once for each function it appears in
make[3]: *** [mm/kasan/common.o] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [mm/kasan] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [mm/] Error 2
make: *** [sub-make] Error 2

An automated git bisect-run points at this:

5c36287813721999e79ac76f637f1ba7e5054402 is the first bad commit
commit 5c36287813721999e79ac76f637f1ba7e5054402
Author: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Date:   Wed Dec 5 11:13:21 2018 +1100

    kasan: initialize shadow to 0xff for tag-based mode

A quick look at the commit makes me think that the case where the

"# CONFIG_KASAN_GENERIC is not set" has not been handled.

I'm using an older gcc 4.8.3 - only used for build testing.

Paul.

--

 mm/kasan/common.c          |  3 ++-
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 4ebc19422931..7a4a0904cac8 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -43,6 +43,15 @@ static phys_addr_t __init kasan_alloc_zeroed_page(int node)
        return __pa(p);
 }

+static phys_addr_t __init kasan_alloc_raw_page(int node)
+{
+       void *p = memblock_alloc_try_nid_raw(PAGE_SIZE, PAGE_SIZE,
+                                               __pa(MAX_DMA_ADDRESS),
+                                               MEMBLOCK_ALLOC_ACCESSIBLE,
+                                               node);
+       return __pa(p);
+}
+
 static pte_t *__init kasan_pte_offset(pmd_t *pmdp, unsigned long addr, int node,
                                      bool early)
 {
@@ -92,7 +101,9 @@ static void __init kasan_pte_populate(pmd_t *pmdp, unsigned long addr,
        do {
                phys_addr_t page_phys = early ?
                                __pa_symbol(kasan_early_shadow_page)
-                                       : kasan_alloc_zeroed_page(node);
+                                       : kasan_alloc_raw_page(node);
+               if (!early)
+                       memset(__va(page_phys), KASAN_SHADOW_INIT, PAGE_SIZE);
                next = addr + PAGE_SIZE;
                set_pte(ptep, pfn_pte(__phys_to_pfn(page_phys), PAGE_KERNEL));
        } while (ptep++, addr = next, addr != end && pte_none(READ_ONCE(*ptep)));
@@ -239,7 +250,7 @@ void __init kasan_init(void)
                        pfn_pte(sym_to_pfn(kasan_early_shadow_page),
                                PAGE_KERNEL_RO));

-       memset(kasan_early_shadow_page, 0, PAGE_SIZE);
+       memset(kasan_early_shadow_page, KASAN_SHADOW_INIT, PAGE_SIZE);
        cpu_replace_ttbr1(lm_alias(swapper_pg_dir));

        /* At this point kasan is fully initialized. Enable error messages */
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index ec22d548d0d7..c56af24bd3e7 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -153,6 +153,8 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }

 #ifdef CONFIG_KASAN_GENERIC

+#define KASAN_SHADOW_INIT 0
+
 void kasan_cache_shrink(struct kmem_cache *cache);
 void kasan_cache_shutdown(struct kmem_cache *cache);

@@ -163,4 +165,10 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}

 #endif /* CONFIG_KASAN_GENERIC */

+#ifdef CONFIG_KASAN_SW_TAGS
+
+#define KASAN_SHADOW_INIT 0xFF
+
+#endif /* CONFIG_KASAN_SW_TAGS */
+
 #endif /* LINUX_KASAN_H */
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 5f68c93734ba..7134e75447ff 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -473,11 +473,12 @@ int kasan_module_alloc(void *addr, size_t size)

        ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
                        shadow_start + shadow_size,
-                       GFP_KERNEL | __GFP_ZERO,
+                       GFP_KERNEL,
                        PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
                        __builtin_return_address(0));

        if (ret) {
+               __memset(ret, KASAN_SHADOW_INIT, shadow_size);
                find_vm_area(addr)->flags |= VM_KASAN;
                kmemleak_ignore(ret);
                return 0;
--
2.20.0.rc1.387.gf8505762e3-goog