linux-kernel - Re: [PATCH] PNP: fix unintended sign extension on left shifts

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Date:   Tue, 15 Oct 2019 18:29:32 +0200
From:   "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Jaroslav Kysela <perex@...ex.cz>, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PNP: fix unintended sign extension on left shifts

On 10/14/2019 3:16 PM, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
>
> Shifting a u8 left will cause the value to be promoted to an integer. If
> the top bit of the u8 is set then the following conversion to a 64 bit
> resource_size_t will sign extend the value causing the upper 32 bits
> to be set in the result.
>
> Fix this by casting the u8 value to a resource_size_t before the shift.
> Original commit is pre-git history.
>
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Please resend this with a Cc to linux-acpi@...r.kernel.org for easier 
handling.


> ---
>   drivers/pnp/isapnp/core.c | 18 ++++++++++++------
>   1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/pnp/isapnp/core.c b/drivers/pnp/isapnp/core.c
> index 179b737280e1..c947b1673041 100644
> --- a/drivers/pnp/isapnp/core.c
> +++ b/drivers/pnp/isapnp/core.c
> @@ -511,10 +511,14 @@ static void __init isapnp_parse_mem32_resource(struct pnp_dev *dev,
>   	unsigned char flags;
>   
>   	isapnp_peek(tmp, size);
> -	min = (tmp[4] << 24) | (tmp[3] << 16) | (tmp[2] << 8) | tmp[1];
> -	max = (tmp[8] << 24) | (tmp[7] << 16) | (tmp[6] << 8) | tmp[5];
> -	align = (tmp[12] << 24) | (tmp[11] << 16) | (tmp[10] << 8) | tmp[9];
> -	len = (tmp[16] << 24) | (tmp[15] << 16) | (tmp[14] << 8) | tmp[13];
> +	min = ((resource_size_t)tmp[4] << 24) | (tmp[3] << 16) |
> +              (tmp[2] << 8) | tmp[1];
> +	max = ((resource_size_t)tmp[8] << 24) | (tmp[7] << 16) |
> +              (tmp[6] << 8) | tmp[5];
> +	align = ((resource_size_t)tmp[12] << 24) | (tmp[11] << 16) |
> +              (tmp[10] << 8) | tmp[9];
> +	len = ((resource_size_t)tmp[16] << 24) | (tmp[15] << 16) |
> +              (tmp[14] << 8) | tmp[13];
>   	flags = tmp[0];
>   	pnp_register_mem_resource(dev, option_flags,
>   				  min, max, align, len, flags);
> @@ -532,8 +536,10 @@ static void __init isapnp_parse_fixed_mem32_resource(struct pnp_dev *dev,
>   	unsigned char flags;
>   
>   	isapnp_peek(tmp, size);
> -	base = (tmp[4] << 24) | (tmp[3] << 16) | (tmp[2] << 8) | tmp[1];
> -	len = (tmp[8] << 24) | (tmp[7] << 16) | (tmp[6] << 8) | tmp[5];
> +	base = ((resource_size_t)tmp[4] << 24) | (tmp[3] << 16) |
> +	       (tmp[2] << 8) | tmp[1];
> +	len = ((resource_size_t)tmp[8] << 24) | (tmp[7] << 16) |
> +              (tmp[6] << 8) | tmp[5];
>   	flags = tmp[0];
>   	pnp_register_mem_resource(dev, option_flags, base, base, 0, len, flags);
>   }