linux-kernel - Re: [PATCH 1/3] of: Fix truncation of memory sizes on 32-bit platforms

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Message-ID: <0c2be5ec-8a22-d398-d455-847ddbcece86@samsung.com>
Date:   Wed, 16 Jun 2021 11:36:42 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] of: Fix truncation of memory sizes on 32-bit
 platforms

On 16.06.2021 11:27, Geert Uytterhoeven wrote:
> Variable "size" has type "phys_addr_t", which can be either 32-bit or
> 64-bit on 32-bit systems, while "unsigned long" is always 32-bit on
> 32-bit systems.  Hence the cast in
>
>      (unsigned long)size / SZ_1M
>
> may truncate a 64-bit size to 32-bit, as casts have a higher operator
> precedence than divisions.
>
> Fix this by inverting the order of the cast and division, which should
> be safe for memory blocks smaller than 4 PiB.  Note that the division is
> actually a shift, as SZ_1M is a power-of-two constant, hence there is no
> need to use div_u64().
>
> While at it, use "%lu" to format "unsigned long".
>
> Fixes: e8d9d1f5485b52ec ("drivers: of: add initialization code for static reserved memory")
> Fixes: 3f0c8206644836e4 ("drivers: of: add initialization code for dynamic reserved memory")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
Acked-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>   drivers/of/fdt.c             | 8 ++++----
>   drivers/of/of_reserved_mem.c | 8 ++++----
>   2 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index a03d43f95495d8e1..970fa8cdc9303195 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -510,11 +510,11 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
>   
>   		if (size &&
>   		    early_init_dt_reserve_memory_arch(base, size, nomap) == 0)
> -			pr_debug("Reserved memory: reserved region for node '%s': base %pa, size %ld MiB\n",
> -				uname, &base, (unsigned long)size / SZ_1M);
> +			pr_debug("Reserved memory: reserved region for node '%s': base %pa, size %lu MiB\n",
> +				uname, &base, (unsigned long)(size / SZ_1M));
>   		else
> -			pr_info("Reserved memory: failed to reserve memory for node '%s': base %pa, size %ld MiB\n",
> -				uname, &base, (unsigned long)size / SZ_1M);
> +			pr_info("Reserved memory: failed to reserve memory for node '%s': base %pa, size %lu MiB\n",
> +				uname, &base, (unsigned long)(size / SZ_1M));
>   
>   		len -= t_len;
>   		if (first) {
> diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
> index 4592b71aba5cf4a1..333d33bad59d7888 100644
> --- a/drivers/of/of_reserved_mem.c
> +++ b/drivers/of/of_reserved_mem.c
> @@ -136,9 +136,9 @@ static int __init __reserved_mem_alloc_size(unsigned long node,
>   			ret = early_init_dt_alloc_reserved_memory_arch(size,
>   					align, start, end, nomap, &base);
>   			if (ret == 0) {
> -				pr_debug("allocated memory for '%s' node: base %pa, size %ld MiB\n",
> +				pr_debug("allocated memory for '%s' node: base %pa, size %lu MiB\n",
>   					uname, &base,
> -					(unsigned long)size / SZ_1M);
> +					(unsigned long)(size / SZ_1M));
>   				break;
>   			}
>   			len -= t_len;
> @@ -148,8 +148,8 @@ static int __init __reserved_mem_alloc_size(unsigned long node,
>   		ret = early_init_dt_alloc_reserved_memory_arch(size, align,
>   							0, 0, nomap, &base);
>   		if (ret == 0)
> -			pr_debug("allocated memory for '%s' node: base %pa, size %ld MiB\n",
> -				uname, &base, (unsigned long)size / SZ_1M);
> +			pr_debug("allocated memory for '%s' node: base %pa, size %lu MiB\n",
> +				uname, &base, (unsigned long)(size / SZ_1M));
>   	}
>   
>   	if (base == 0) {

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland