linux-kernel - Re: [PATCH][V2] x86/apic: fix integer overflow on 10 bit left shift of cpu

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Date:   Thu, 20 Jun 2019 10:59:59 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][V2] x86/apic: fix integer overflow on 10 bit left shift
 of cpu_khz

On Wed, Jun 19, 2019 at 07:14:46PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The left shift of unsigned int cpu_khz will overflow for large values
> of cpu_khz, so cast it to a long long before shifting it to avoid
> overvlow.  For example, this can happen when cpu_khz is 4194305 (just
> less than 4.2 GHz).  Also wrap line to avoid checkpatch wide line
> warning.
> 
> Addresses-Coverity: ("Unintentional integer overflow")
> Fixes: 8c3ba8d04924 ("x86, apic: ack all pending irqs when crashed/on kexec")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  arch/x86/kernel/apic/apic.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 8956072f677d..31426126e5e0 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -1464,7 +1464,8 @@ static void apic_pending_intr_clear(void)
>  		if (queued) {
>  			if (boot_cpu_has(X86_FEATURE_TSC) && cpu_khz) {
>  				ntsc = rdtsc();
> -				max_loops = (cpu_khz << 10) - (ntsc - tsc);
> +				max_loops = ((long long)cpu_khz << 10) -
> +					    (ntsc - tsc);
>  			} else {
>  				max_loops--;
>  			}
> -- 
> 
> V2: replace right with left in commit subject and message. Doh.
> 

Uh, why are you putting the v2 explanation here instead of between the
--- cut off and the diffstat/


regards,
dan carpenter