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 <redacted>
---
 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