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

From: Thomas Gleixner <tglx@linutronix.de>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	kernel-janitors@vger.kernel.org
Subject: Re: [PATCH] x86/ioremap: tighten integer overflow checking
Date: Mon, 29 Oct 2018 19:34:58 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1810291925470.5984@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20181025061633.t32bxslxj3h7jv2x@kili.mountain>

Dan,

On Thu, 25 Oct 2018, 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.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.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)

Assume the following (resource_size_t == u32, which is the case when
CONFIG_PHYS_ADDR_T_64BIT=n):

       phys_addr = 0xFFFF0000
       size	 = 0x00010000

       sum	 = 0x00000000  which is < phys_addr

But the existing code does:

       last_addr = phys_addr + size - 1

       		 = 0xFFFFFFFF

which is correct. last_addr is the last valid address in the to be remapped
range starting @phys_addr.

Thanks,

	tglx