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SubjectRe: [PATCH v2] mm/kasan: Print frame description for stack bugs
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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.


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