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Subject: Re: [PATCH v2] mm/kasan: Print frame description for stack bugs
To:     Marco Elver <elver@google.com>, dvyukov@google.com,
        glider@google.com, andreyknvl@google.com, akpm@linux-foundation.org
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        kasan-dev@googlegroups.com
References: <20190520154751.84763-1-elver@google.com>
From:   Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <ebec4325-f91b-b392-55ed-95dbd36bbb8e@virtuozzo.com>
Date:   Tue, 21 May 2019 18:43:54 +0300
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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.