Re: mmotm 2020-03-03-22-28 uploaded (warning: objtool:)

Peter Zijlstra
2020-03-05T08:17:30Z

On Wed, Mar 04, 2020 at 09:34:49AM -0800, Randy Dunlap wrote:
> On 3/3/20 10:28 PM, akpm@linux-foundation.org wrote:
> > The mm-of-the-moment snapshot 2020-03-03-22-28 has been uploaded to
> >
> > http://www.ozlabs.org/~akpm/mmotm/
> >
> > mmotm-readme.txt says
> >
> > README for mm-of-the-moment:
> >
> > http://www.ozlabs.org/~akpm/mmotm/
> >
> > This is a snapshot of my -mm patch queue. Uploaded at random hopefully
> > more than once a week.
> >
> > You will need quilt to apply these patches to the latest Linus release (5.x
> > or 5.x-rcY). The series file is in broken-out.tar.gz and is duplicated in
> > http://ozlabs.org/~akpm/mmotm/series
>
> on x86_64:
>
> mm/kasan/common.o: warning: objtool: kasan_report()+0x13: call to report_enabled() with UACCESS enabled

I used next/master instead, and found the below broken commit
responsible for this.

---

commit 97f4ea76d4f40a401b84825f038710c9a96ec294
Author: Walter Wu <walter-zh.wu@mediatek.com>
Date: Wed Mar 4 22:31:15 2020 +1100

kasan: detect negative size in memory operation function

Patch series "fix the missing underflow in memory operation function", v4.

The patchset helps to produce a KASAN report when size is negative in
memory operation functions. It is helpful for programmer to solve an
undefined behavior issue. Patch 1 based on Dmitry's review and
suggestion, patch 2 is a test in order to verify the patch 1.

[1]https://bugzilla.kernel.org/show_bug.cgi?id=199341
[2]https://lore.kernel.org/linux-arm-kernel/20190927034338.15813-1-walter-zh.wu@mediatek.com/

This patch (of 2):

KASAN missed detecting size is a negative number in memset(), memcpy(),
and memmove(), it will cause out-of-bounds bug. So needs to be detected
by KASAN.

If size is a negative number, then it has a reason to be defined as
out-of-bounds bug type. Casting negative numbers to size_t would indeed
turn up as a large size_t and its value will be larger than ULONG_MAX/2,
so that this can qualify as out-of-bounds.

KASAN report is shown below:

BUG: KASAN: out-of-bounds in kmalloc_memmove_invalid_size+0x70/0xa0
Read of size 18446744073709551608 at addr ffffff8069660904 by task cat/72

CPU: 2 PID: 72 Comm: cat Not tainted 5.4.0-rc1-next-20191004ajb-00001-gdb8af2f372b2-dirty #1
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0x0/0x288
show_stack+0x14/0x20
dump_stack+0x10c/0x164
print_address_description.isra.9+0x68/0x378
__kasan_report+0x164/0x1a0
kasan_report+0xc/0x18
check_memory_region+0x174/0x1d0
memmove+0x34/0x88
kmalloc_memmove_invalid_size+0x70/0xa0

[1] https://bugzilla.kernel.org/show_bug.cgi?id=199341

Link: http://lkml.kernel.org/r/20191112065302.7015-1-walter-zh.wu@mediatek.com
Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 5cde9e7c2664..31314ca7c635 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -190,7 +190,7 @@ void kasan_init_tags(void);

void *kasan_reset_tag(const void *addr);

-void kasan_report(unsigned long addr, size_t size,
+bool kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);

#else /* CONFIG_KASAN_SW_TAGS */
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 6aa51723b92b..c798b12323d7 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -105,7 +105,8 @@ EXPORT_SYMBOL(__kasan_check_write);
#undef memset
void *memset(void *addr, int c, size_t len)
{
- check_memory_region((unsigned long)addr, len, true, _RET_IP_);
+ if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_))
+ return NULL;

return __memset(addr, c, len);
}
@@ -114,8 +115,9 @@ void *memset(void *addr, int c, size_t len)
#undef memmove
void *memmove(void *dest, const void *src, size_t len)
{
- check_memory_region((unsigned long)src, len, false, _RET_IP_);
- check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+ if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
+ !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
+ return NULL;

return __memmove(dest, src, len);
}
@@ -124,8 +126,9 @@ void *memmove(void *dest, const void *src, size_t len)
#undef memcpy
void *memcpy(void *dest, const void *src, size_t len)
{
- check_memory_region((unsigned long)src, len, false, _RET_IP_);
- check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+ if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
+ !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
+ return NULL;

return __memcpy(dest, src, len);
}
@@ -634,12 +637,20 @@ void kasan_free_shadow(const struct vm_struct *vm)
#endif

extern void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip);
+extern bool report_enabled(void);

-void kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
+bool kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
{
- unsigned long flags = user_access_save();
+ unsigned long flags;
+
+ if (likely(!report_enabled()))
+ return false;
+
+ flags = user_access_save();
__kasan_report(addr, size, is_write, ip);
user_access_restore(flags);
+
+ return true;
}

#ifdef CONFIG_MEMORY_HOTPLUG
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 616f9dd82d12..56ff8885fe2e 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -173,17 +173,18 @@ static __always_inline bool check_memory_region_inline(unsigned long addr,
if (unlikely(size == 0))
return true;

+ if (unlikely(addr + size < addr))
+ return !kasan_report(addr, size, write, ret_ip);
+
if (unlikely((void *)addr <
kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
- kasan_report(addr, size, write, ret_ip);
- return false;
+ return !kasan_report(addr, size, write, ret_ip);
}

if (likely(!memory_is_poisoned(addr, size)))
return true;

- kasan_report(addr, size, write, ret_ip);
- return false;
+ return !kasan_report(addr, size, write, ret_ip);
}

bool check_memory_region(unsigned long addr, size_t size, bool write,
diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
index 2d97efd4954f..e200acb2d292 100644
--- a/mm/kasan/generic_report.c
+++ b/mm/kasan/generic_report.c
@@ -110,6 +110,17 @@ static const char *get_wild_bug_type(struct kasan_access_info *info)

const char *get_bug_type(struct kasan_access_info *info)
{
+ /*
+ * If access_size is a negative number, then it has reason to be
+ * defined as out-of-bounds bug type.
+ *
+ * Casting negative numbers to size_t would indeed turn up as
+ * a large size_t and its value will be larger than ULONG_MAX/2,
+ * so that this can qualify as out-of-bounds.
+ */
+ if (info->access_addr + info->access_size < info->access_addr)
+ return "out-of-bounds";
+
if (addr_has_shadow(info->access_addr))
return get_shadow_bug_type(info);
return get_wild_bug_type(info);
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 3a083274628e..e8f37199d885 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -153,7 +153,7 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
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,
+bool 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/report.c b/mm/kasan/report.c
index 5ef9f24f566b..cf5c17d5e361 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -446,7 +446,7 @@ static void print_shadow_for_address(const void *addr)
}
}

-static bool report_enabled(void)
+bool report_enabled(void)
{
if (current->kasan_depth)
return false;
@@ -478,9 +478,6 @@ void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned lon
void *untagged_addr;
unsigned long flags;

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

tagged_addr = (void *)addr;
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 0e987c9ca052..25b7734e7013 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -86,6 +86,9 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
if (unlikely(size == 0))
return true;

+ if (unlikely(addr + size < addr))
+ return !kasan_report(addr, size, write, ret_ip);
+
tag = get_tag((const void *)addr);

/*
@@ -111,15 +114,13 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
untagged_addr = reset_tag((const void *)addr);
if (unlikely(untagged_addr <
kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
- kasan_report(addr, size, write, ret_ip);
- return false;
+ return !kasan_report(addr, size, write, ret_ip);
}
shadow_first = kasan_mem_to_shadow(untagged_addr);
shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
if (*shadow != tag) {
- kasan_report(addr, size, write, ret_ip);
- return false;
+ return !kasan_report(addr, size, write, ret_ip);
}
}

diff --git a/mm/kasan/tags_report.c b/mm/kasan/tags_report.c
index 969ae08f59d7..1d412760551a 100644
--- a/mm/kasan/tags_report.c
+++ b/mm/kasan/tags_report.c
@@ -36,6 +36,17 @@

const char *get_bug_type(struct kasan_access_info *info)
{
+ /*
+ * If access_size is a negative number, then it has reason to be
+ * defined as out-of-bounds bug type.
+ *
+ * Casting negative numbers to size_t would indeed turn up as
+ * a large size_t and its value will be larger than ULONG_MAX/2,
+ * so that this can qualify as out-of-bounds.
+ */
+ if (info->access_addr + info->access_size < info->access_addr)
+ return "out-of-bounds";
+
#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
struct kasan_alloc_meta *alloc_meta;
struct kmem_cache *cache;