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Subject[PATCH v6 13/18] khwasan: add bug reporting routines
Date
This commit adds rountines, that print KHWASAN error reports. Those are
quite similar to KASAN, the difference is:

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

2. KHWASAN reports all bugs with the "KASAN: invalid-access" header. This
is done, so various external tools that already parse the kernel logs
looking for KASAN reports wouldn't need to be changed.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
include/linux/kasan.h | 3 +++
mm/kasan/kasan.h | 7 +++++
mm/kasan/kasan_report.c | 7 ++---
mm/kasan/khwasan_report.c | 21 +++++++++++++++
mm/kasan/report.c | 57 +++++++++++++++++++++------------------
5 files changed, 64 insertions(+), 31 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 1f852244e739..4424359a9dfa 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -174,6 +174,9 @@ void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr);
void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
const void *addr);

+void kasan_report(unsigned long addr, size_t size,
+ bool write, unsigned long ip);
+
#else /* CONFIG_KASAN_HW */

static inline void khwasan_init(void) { }
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 82672473740c..d60859d26be7 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -119,8 +119,15 @@ 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);

+#ifdef CONFIG_KASAN_HW
+void print_tags(u8 addr_tag, const void *addr);
+#else
+static inline void print_tags(u8 addr_tag, const void *addr) { }
+#endif
+
void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
void kasan_report_invalid_free(void *object, unsigned long ip);
diff --git a/mm/kasan/kasan_report.c b/mm/kasan/kasan_report.c
index 2d8decbecbd5..fdf2d77e3125 100644
--- a/mm/kasan/kasan_report.c
+++ b/mm/kasan/kasan_report.c
@@ -33,10 +33,10 @@
#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 *first_bad_addr = addr;

while (!shadow_val && first_bad_addr < addr + size) {
first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
@@ -50,9 +50,6 @@ 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/khwasan_report.c b/mm/kasan/khwasan_report.c
index 2edbc3c76be5..51238b404b08 100644
--- a/mm/kasan/khwasan_report.c
+++ b/mm/kasan/khwasan_report.c
@@ -37,3 +37,24 @@ 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 *untagged_addr = reset_tag(addr);
+ u8 *shadow = (u8 *)kasan_mem_to_shadow(untagged_addr);
+ void *first_bad_addr = untagged_addr;
+
+ while (*shadow == tag && first_bad_addr < untagged_addr + size) {
+ first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
+ shadow = (u8 *)kasan_mem_to_shadow(first_bad_addr);
+ }
+ return first_bad_addr;
+}
+
+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);
+}
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 155247a6f8a8..e031c78f2e52 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);
}
--
2.19.0.rc0.228.g281dcd1b4d0-goog
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