This adds support for printing stack frame description on invalid stack
accesses. The frame description is embedded by the compiler, which is
parsed and then pretty-printed.
Currently, we can only print the stack frame info for accesses to the
task's own stack, but not accesses to other tasks' stacks.
Example of what it looks like:
[ 17.924050] page dumped because: kasan: bad access detected
[ 17.924908]
[ 17.925153] addr ffff8880673ef98a is located in stack of task insmod/2008 at offset 106 in frame:
[ 17.926542] kasan_stack_oob+0x0/0xf5 [test_kasan]
[ 17.927932]
[ 17.928206] this frame has 2 objects:
[ 17.928783] [32, 36) 'i'
[ 17.928784] [96, 106) 'stack_array'
[ 17.929216]
[ 17.930031] Memory state around the buggy address:
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=198435
Signed-off-by: Marco Elver <[email protected]>
---
Changes since V1:
- Fix types in printf (%zu -> %lu).
- Prefer 'unsigned long', to ensure offsets/addrs are pointer sized, as
emitted by ASAN instrumentation.
Change-Id: I4836cde103052991ac8871796a45b4c977c9e2e7
---
mm/kasan/kasan.h | 5 ++
mm/kasan/report.c | 163 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 168 insertions(+)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 3ce956efa0cb..1979db4763e2 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -43,6 +43,11 @@
#define KASAN_ALLOCA_REDZONE_SIZE 32
+/*
+ * Stack frame marker (compiler ABI).
+ */
+#define KASAN_CURRENT_STACK_FRAME_MAGIC 0x41B58AB3
+
/* Don't break randconfig/all*config builds */
#ifndef KASAN_ABI_VERSION
#define KASAN_ABI_VERSION 1
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 03a443579386..36e55956acaf 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -28,6 +28,7 @@
#include <linux/types.h>
#include <linux/kasan.h>
#include <linux/module.h>
+#include <linux/sched/task_stack.h>
#include <asm/sections.h>
@@ -181,6 +182,166 @@ static inline bool init_task_stack_addr(const void *addr)
sizeof(init_thread_union.stack));
}
+static bool __must_check tokenize_frame_descr(const char **frame_descr,
+ char *token, size_t max_tok_len,
+ unsigned long *value)
+{
+ const char *sep = strchr(*frame_descr, ' ');
+
+ if (sep == NULL)
+ sep = *frame_descr + strlen(*frame_descr);
+
+ if (token != NULL) {
+ const size_t tok_len = sep - *frame_descr;
+
+ if (tok_len + 1 > max_tok_len) {
+ pr_err("KASAN internal error: frame description too long: %s\n",
+ *frame_descr);
+ return false;
+ }
+
+ /* Copy token (+ 1 byte for '\0'). */
+ strlcpy(token, *frame_descr, tok_len + 1);
+ }
+
+ /* Advance frame_descr past separator. */
+ *frame_descr = sep + 1;
+
+ if (value != NULL && kstrtoul(token, 10, value)) {
+ pr_err("KASAN internal error: not a valid number: %s\n", token);
+ return false;
+ }
+
+ return true;
+}
+
+static void print_decoded_frame_descr(const char *frame_descr)
+{
+ /*
+ * We need to parse the following string:
+ * "n alloc_1 alloc_2 ... alloc_n"
+ * where alloc_i looks like
+ * "offset size len name"
+ * or "offset size len name:line".
+ */
+
+ char token[64];
+ unsigned long num_objects;
+
+ if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
+ &num_objects))
+ return;
+
+ pr_err("\n");
+ pr_err("this frame has %lu %s:\n", num_objects,
+ num_objects == 1 ? "object" : "objects");
+
+ while (num_objects--) {
+ unsigned long offset;
+ unsigned long size;
+
+ /* access offset */
+ if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
+ &offset))
+ return;
+ /* access size */
+ if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
+ &size))
+ return;
+ /* name length (unused) */
+ if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
+ return;
+ /* object name */
+ if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
+ NULL))
+ return;
+
+ /* Strip line number, if it exists. */
+ strreplace(token, ':', '\0');
+
+ /* Finally, print object information. */
+ pr_err(" [%lu, %lu) '%s'", offset, offset + size, token);
+ }
+}
+
+static bool __must_check get_address_stack_frame_info(const void *addr,
+ unsigned long *offset,
+ const char **frame_descr,
+ const void **frame_pc)
+{
+ unsigned long aligned_addr;
+ unsigned long mem_ptr;
+ const u8 *shadow_bottom;
+ const u8 *shadow_ptr;
+ const unsigned long *frame;
+
+ /*
+ * NOTE: We currently only support printing frame information for
+ * accesses to the task's own stack.
+ */
+ if (!object_is_on_stack(addr))
+ return false;
+
+ aligned_addr = round_down((unsigned long)addr, sizeof(long));
+ mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
+ shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
+ shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
+
+ while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
+ shadow_ptr--;
+ mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
+ }
+
+ while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
+ shadow_ptr--;
+ mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
+ }
+
+ if (shadow_ptr < shadow_bottom)
+ return false;
+
+ frame = (const unsigned long *)(mem_ptr + KASAN_SHADOW_SCALE_SIZE);
+ if (frame[0] != KASAN_CURRENT_STACK_FRAME_MAGIC) {
+ pr_err("KASAN internal error: frame info validation failed; invalid marker: %lu\n",
+ frame[0]);
+ return false;
+ }
+
+ *offset = (unsigned long)addr - (unsigned long)frame;
+ *frame_descr = (const char *)frame[1];
+ *frame_pc = (void *)frame[2];
+
+ return true;
+}
+
+static void print_address_stack_frame(const void *addr)
+{
+ unsigned long offset;
+ const char *frame_descr;
+ const void *frame_pc;
+
+ if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
+ return;
+
+ if (!get_address_stack_frame_info(addr, &offset, &frame_descr,
+ &frame_pc))
+ return;
+
+ /*
+ * get_address_stack_frame_info only returns true if the given addr is
+ * on the current task's stack.
+ */
+ pr_err("\n");
+ pr_err("addr %px is located in stack of task %s/%d at offset %lu in frame:\n",
+ addr, current->comm, task_pid_nr(current), offset);
+ pr_err(" %pS\n", frame_pc);
+
+ if (!frame_descr)
+ return;
+
+ print_decoded_frame_descr(frame_descr);
+}
+
static void print_address_description(void *addr)
{
struct page *page = addr_to_page(addr);
@@ -204,6 +365,8 @@ static void print_address_description(void *addr)
pr_err("The buggy address belongs to the page:\n");
dump_page(page, "kasan: bad access detected");
}
+
+ print_address_stack_frame(addr);
}
static bool row_is_guilty(const void *row, const void *guilty)
--
2.21.0.1020.gf2820cf01a-goog
On 5/20/19 6:47 PM, Marco Elver wrote:
> +static void print_decoded_frame_descr(const char *frame_descr)
> +{
> + /*
> + * We need to parse the following string:
> + * "n alloc_1 alloc_2 ... alloc_n"
> + * where alloc_i looks like
> + * "offset size len name"
> + * or "offset size len name:line".
> + */
> +
> + char token[64];
> + unsigned long num_objects;
> +
> + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> + &num_objects))
> + return;
> +
> + pr_err("\n");
> + pr_err("this frame has %lu %s:\n", num_objects,
> + num_objects == 1 ? "object" : "objects");
> +
> + while (num_objects--) {
> + unsigned long offset;
> + unsigned long size;
> +
> + /* access offset */
> + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> + &offset))
> + return;
> + /* access size */
> + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> + &size))
> + return;
> + /* name length (unused) */
> + if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
> + return;
> + /* object name */
> + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> + NULL))
> + return;
> +
> + /* Strip line number, if it exists. */
Why?
> + strreplace(token, ':', '\0');
> +
...
> +
> + aligned_addr = round_down((unsigned long)addr, sizeof(long));
> + mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
> + shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
> + shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
> +
> + while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
> + shadow_ptr--;
> + mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
> + }
> +
> + while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
> + shadow_ptr--;
> + mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
> + }
> +
I suppose this won't work if stack grows up, which is fine because it grows up only on parisc arch.
But "BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROUWSUP))" somewhere wouldn't hurt.
On Tue, May 21, 2019 at 5:43 PM Andrey Ryabinin <[email protected]> wrote:
>
>
>
> On 5/20/19 6:47 PM, Marco Elver wrote:
>
> > +static void print_decoded_frame_descr(const char *frame_descr)
> > +{
> > + /*
> > + * We need to parse the following string:
> > + * "n alloc_1 alloc_2 ... alloc_n"
> > + * where alloc_i looks like
> > + * "offset size len name"
> > + * or "offset size len name:line".
> > + */
> > +
> > + char token[64];
> > + unsigned long num_objects;
> > +
> > + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> > + &num_objects))
> > + return;
> > +
> > + pr_err("\n");
> > + pr_err("this frame has %lu %s:\n", num_objects,
> > + num_objects == 1 ? "object" : "objects");
> > +
> > + while (num_objects--) {
> > + unsigned long offset;
> > + unsigned long size;
> > +
> > + /* access offset */
> > + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> > + &offset))
> > + return;
> > + /* access size */
> > + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> > + &size))
> > + return;
> > + /* name length (unused) */
> > + if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
> > + return;
> > + /* object name */
> > + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> > + NULL))
> > + return;
> > +
> > + /* Strip line number, if it exists. */
>
> Why?
>
> > + strreplace(token, ':', '\0');
> > +
>
> ...
>
> > +
> > + aligned_addr = round_down((unsigned long)addr, sizeof(long));
> > + mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
> > + shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
> > + shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
> > +
> > + while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
> > + shadow_ptr--;
> > + mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
> > + }
> > +
> > + while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
> > + shadow_ptr--;
> > + mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
> > + }
> > +
>
> I suppose this won't work if stack grows up, which is fine because it grows up only on parisc arch.
> But "BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROUWSUP))" somewhere wouldn't hurt.
Note that KASAN was broken on parisc from day 1 because of other
assumptions on the stack growth direction hardcoded into KASAN
(e.g. __kasan_unpoison_stack() and __asan_allocas_unpoison()).
So maybe this BUILD_BUG_ON can be added in a separate patch as it's
not specific to what Marco is doing here?
>
> --
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--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
On Tue, 21 May 2019 at 17:53, Alexander Potapenko <[email protected]> wrote:
>
> On Tue, May 21, 2019 at 5:43 PM Andrey Ryabinin <[email protected]> wrote:
> >
> > On 5/20/19 6:47 PM, Marco Elver wrote:
> >
> > > +static void print_decoded_frame_descr(const char *frame_descr)
> > > +{
> > > + /*
> > > + * We need to parse the following string:
> > > + * "n alloc_1 alloc_2 ... alloc_n"
> > > + * where alloc_i looks like
> > > + * "offset size len name"
> > > + * or "offset size len name:line".
> > > + */
> > > +
> > > + char token[64];
> > > + unsigned long num_objects;
> > > +
> > > + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> > > + &num_objects))
> > > + return;
> > > +
> > > + pr_err("\n");
> > > + pr_err("this frame has %lu %s:\n", num_objects,
> > > + num_objects == 1 ? "object" : "objects");
> > > +
> > > + while (num_objects--) {
> > > + unsigned long offset;
> > > + unsigned long size;
> > > +
> > > + /* access offset */
> > > + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> > > + &offset))
> > > + return;
> > > + /* access size */
> > > + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> > > + &size))
> > > + return;
> > > + /* name length (unused) */
> > > + if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
> > > + return;
> > > + /* object name */
> > > + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
> > > + NULL))
> > > + return;
> > > +
> > > + /* Strip line number, if it exists. */
> >
> > Why?
The filename is not included, and I don't think it adds much in terms
of ability to debug; nor is the line number included with all
descriptions. I think, the added complexity of separating the line
number and parsing is not worthwhile here. Alternatively, I could not
pay attention to the line number at all, and leave it as is -- in that
case, some variable names will display as "foo:123".
> >
> > > + strreplace(token, ':', '\0');
> > > +
> >
> > ...
> >
> > > +
> > > + aligned_addr = round_down((unsigned long)addr, sizeof(long));
> > > + mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
> > > + shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
> > > + shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
> > > +
> > > + while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
> > > + shadow_ptr--;
> > > + mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
> > > + }
> > > +
> > > + while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
> > > + shadow_ptr--;
> > > + mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
> > > + }
> > > +
> >
> > I suppose this won't work if stack grows up, which is fine because it grows up only on parisc arch.
> > But "BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROUWSUP))" somewhere wouldn't hurt.
> Note that KASAN was broken on parisc from day 1 because of other
> assumptions on the stack growth direction hardcoded into KASAN
> (e.g. __kasan_unpoison_stack() and __asan_allocas_unpoison()).
> So maybe this BUILD_BUG_ON can be added in a separate patch as it's
> not specific to what Marco is doing here?
Happy to send a follow-up patch, or add here. Let me know what you prefer.
Thanks,
-- Marco
On 5/21/19 7:07 PM, Marco Elver wrote:
> On Tue, 21 May 2019 at 17:53, Alexander Potapenko <[email protected]> wrote:
>>
>> On Tue, May 21, 2019 at 5:43 PM Andrey Ryabinin <[email protected]> wrote:
>>>
>>> On 5/20/19 6:47 PM, Marco Elver wrote:
>>>
>>>> +static void print_decoded_frame_descr(const char *frame_descr)
>>>> +{
>>>> + /*
>>>> + * We need to parse the following string:
>>>> + * "n alloc_1 alloc_2 ... alloc_n"
>>>> + * where alloc_i looks like
>>>> + * "offset size len name"
>>>> + * or "offset size len name:line".
>>>> + */
>>>> +
>>>> + char token[64];
>>>> + unsigned long num_objects;
>>>> +
>>>> + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
>>>> + &num_objects))
>>>> + return;
>>>> +
>>>> + pr_err("\n");
>>>> + pr_err("this frame has %lu %s:\n", num_objects,
>>>> + num_objects == 1 ? "object" : "objects");
>>>> +
>>>> + while (num_objects--) {
>>>> + unsigned long offset;
>>>> + unsigned long size;
>>>> +
>>>> + /* access offset */
>>>> + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
>>>> + &offset))
>>>> + return;
>>>> + /* access size */
>>>> + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
>>>> + &size))
>>>> + return;
>>>> + /* name length (unused) */
>>>> + if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
>>>> + return;
>>>> + /* object name */
>>>> + if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
>>>> + NULL))
>>>> + return;
>>>> +
>>>> + /* Strip line number, if it exists. */
>>>
>>> Why?
>
> The filename is not included, and I don't think it adds much in terms
> of ability to debug; nor is the line number included with all
> descriptions. I think, the added complexity of separating the line
> number and parsing is not worthwhile here. Alternatively, I could not
> pay attention to the line number at all, and leave it as is -- in that
> case, some variable names will display as "foo:123".
>
Either way is fine by me. But explain why in comment if you decide
to keep current code. Something like
/* Strip line number cause it's not very helpful. */
>>>
>>>> + strreplace(token, ':', '\0');
>>>> +
>>>
>>> ...
>>>
>>>> +
>>>> + aligned_addr = round_down((unsigned long)addr, sizeof(long));
>>>> + mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
>>>> + shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
>>>> + shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
>>>> +
>>>> + while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
>>>> + shadow_ptr--;
>>>> + mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
>>>> + }
>>>> +
>>>> + while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
>>>> + shadow_ptr--;
>>>> + mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
>>>> + }
>>>> +
>>>
>>> I suppose this won't work if stack grows up, which is fine because it grows up only on parisc arch.
>>> But "BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROUWSUP))" somewhere wouldn't hurt.
>> Note that KASAN was broken on parisc from day 1 because of other
>> assumptions on the stack growth direction hardcoded into KASAN
>> (e.g. __kasan_unpoison_stack() and __asan_allocas_unpoison()).
It's not broken, it doesn't exist.
>> So maybe this BUILD_BUG_ON can be added in a separate patch as it's
>> not specific to what Marco is doing here?
>
I think it's fine to add it in this patch because BUILD_BUG_ON() is just a hint for developers
that this particular function depends on growing down stack. So it's more a property of the function
rather than KASAN in general.
Other functions you mentioned can be marked with BUILD_BUG_ON()s as well, but not in this patch indeed.
> Happy to send a follow-up patch, or add here. Let me know what you prefer.
>
Send v3 please.