linux-kernel - Re: [PATCH] x86/ioremap: tighten integer overflow checking

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Date:   Thu, 25 Oct 2018 08:28:44 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] x86/ioremap: tighten integer overflow checking

On 25/10/2018 08:16, Dan Carpenter wrote:
> The current check is a bit off in the case where "phys_addr + size"
> wraps to zero because then "last_addr" is set to ULONG_MAX which is >=
> phys_addr.

And -2 would be okay?

For 32-bit systems I believe ULONG_MAX is a perfectly valid physical
address.

> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
>  arch/x86/mm/ioremap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index 5378d10f1d31..ee43df3ebe66 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -146,9 +146,9 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
>  	void __iomem *ret_addr;
>  
>  	/* Don't allow wraparound or zero size */
> -	last_addr = phys_addr + size - 1;
> -	if (!size || last_addr < phys_addr)
> +	if (!size || phys_addr + size < phys_addr)
>  		return NULL;
> +	last_addr = phys_addr + size - 1;
>  
>  	if (!phys_addr_valid(phys_addr)) {

Wouldn't it make more sense to test last_addr for being a valid physical
address here?

>  		printk(KERN_WARNING "ioremap: invalid physical address %llx\n",
> 


Juergen