[PATCH v11 17/24] kasan: add bug reporting routines for tag-based mode

Andrey Konovalov
2018-11-19T17:27:29Z

This commit adds rountines, that print tag-based KASAN error reports.
Those are quite similar to generic KASAN, the difference is:

1. The way tag-based KASAN finds the first bad shadow cell (with a
mismatching tag). Tag-based KASAN compares memory tags from the shadow
memory to the pointer tag.

2. Tag-based KASAN reports all bugs with the "KASAN: invalid-access"
header.

Also simplify generic KASAN find_first_bad_addr.

Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
mm/kasan/generic_report.c | 16 ++++-------
mm/kasan/kasan.h | 5 ++++
mm/kasan/report.c | 57 +++++++++++++++++++++------------------
mm/kasan/tags_report.c | 18 +++++++++++++
4 files changed, 59 insertions(+), 37 deletions(-)

diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
index 5201d1770700..a4604cceae59 100644
--- a/mm/kasan/generic_report.c
+++ b/mm/kasan/generic_report.c
@@ -33,16 +33,13 @@
#include "kasan.h"
#include "../slab.h"

-static const void *find_first_bad_addr(const void *addr, size_t size)
+void *find_first_bad_addr(void *addr, size_t size)
{
- u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
- const void *first_bad_addr = addr;
+ void *p = addr;

- while (!shadow_val && first_bad_addr < addr + size) {
- first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
- shadow_val = *(u8 *)kasan_mem_to_shadow(first_bad_addr);
- }
- return first_bad_addr;
+ while (p < addr + size && !(*(u8 *)kasan_mem_to_shadow(p)))
+ p += KASAN_SHADOW_SCALE_SIZE;
+ return p;
}

static const char *get_shadow_bug_type(struct kasan_access_info *info)
@@ -50,9 +47,6 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info)
const char *bug_type = "unknown-crash";
u8 *shadow_addr;

- info->first_bad_addr = find_first_bad_addr(info->access_addr,
- info->access_size);
-
shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);

/*
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 6e808dbc31e8..86fc18a21664 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -119,6 +119,7 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value);
void check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip);

+void *find_first_bad_addr(void *addr, size_t size);
const char *get_bug_type(struct kasan_access_info *info);

void kasan_report(unsigned long addr, size_t size,
@@ -139,10 +140,14 @@ static inline void quarantine_remove_cache(struct kmem_cache *cache) { }

#ifdef CONFIG_KASAN_SW_TAGS

+void print_tags(u8 addr_tag, const void *addr);
+
u8 random_tag(void);

#else

+static inline void print_tags(u8 addr_tag, const void *addr) { }
+
static inline u8 random_tag(void)
{
return 0;
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 64a74f334c45..214d85035f99 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -64,11 +64,10 @@ static int __init kasan_set_multi_shot(char *str)
}
__setup("kasan_multi_shot", kasan_set_multi_shot);

-static void print_error_description(struct kasan_access_info *info,
- const char *bug_type)
+static void print_error_description(struct kasan_access_info *info)
{
pr_err("BUG: KASAN: %s in %pS\n",
- bug_type, (void *)info->ip);
+ get_bug_type(info), (void *)info->ip);
pr_err("%s of size %zu at addr %px by task %s/%d\n",
info->is_write ? "Write" : "Read", info->access_size,
info->access_addr, current->comm, task_pid_nr(current));
@@ -272,6 +271,8 @@ void kasan_report_invalid_free(void *object, unsigned long ip)

start_report(&flags);
pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
+ print_tags(get_tag(object), reset_tag(object));
+ object = reset_tag(object);
pr_err("\n");
print_address_description(object);
pr_err("\n");
@@ -279,41 +280,45 @@ void kasan_report_invalid_free(void *object, unsigned long ip)
end_report(&flags);
}

-static void kasan_report_error(struct kasan_access_info *info)
-{
- unsigned long flags;
-
- start_report(&flags);
-
- print_error_description(info, get_bug_type(info));
- pr_err("\n");
-
- if (!addr_has_shadow(info->access_addr)) {
- dump_stack();
- } else {
- print_address_description((void *)info->access_addr);
- pr_err("\n");
- print_shadow_for_address(info->first_bad_addr);
- }
-
- end_report(&flags);
-}
-
void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip)
{
struct kasan_access_info info;
+ void *tagged_addr;
+ void *untagged_addr;
+ unsigned long flags;

if (likely(!report_enabled()))
return;

disable_trace_on_warning();

- info.access_addr = (void *)addr;
- info.first_bad_addr = (void *)addr;
+ tagged_addr = (void *)addr;
+ untagged_addr = reset_tag(tagged_addr);
+
+ info.access_addr = tagged_addr;
+ if (addr_has_shadow(untagged_addr))
+ info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
+ else
+ info.first_bad_addr = untagged_addr;
info.access_size = size;
info.is_write = is_write;
info.ip = ip;

- kasan_report_error(&info);
+ start_report(&flags);
+
+ print_error_description(&info);
+ if (addr_has_shadow(untagged_addr))
+ print_tags(get_tag(tagged_addr), info.first_bad_addr);
+ pr_err("\n");
+
+ if (addr_has_shadow(untagged_addr)) {
+ print_address_description(untagged_addr);
+ pr_err("\n");
+ print_shadow_for_address(info.first_bad_addr);
+ } else {
+ dump_stack();
+ }
+
+ end_report(&flags);
}
diff --git a/mm/kasan/tags_report.c b/mm/kasan/tags_report.c
index 8af15e87d3bc..573c51d20d09 100644
--- a/mm/kasan/tags_report.c
+++ b/mm/kasan/tags_report.c
@@ -37,3 +37,21 @@ const char *get_bug_type(struct kasan_access_info *info)
{
return "invalid-access";
}
+
+void *find_first_bad_addr(void *addr, size_t size)
+{
+ u8 tag = get_tag(addr);
+ void *p = reset_tag(addr);
+ void *end = p + size;
+
+ while (p < end && tag == *(u8 *)kasan_mem_to_shadow(p))
+ p += KASAN_SHADOW_SCALE_SIZE;
+ return p;
+}
+
+void print_tags(u8 addr_tag, const void *addr)
+{
+ u8 *shadow = (u8 *)kasan_mem_to_shadow(addr);
+
+ pr_err("Pointer tag: [%02x], memory tag: [%02x]\n", addr_tag, *shadow);
+}
--
2.19.1.1215.g8438c0b245-goog