[PATCH][V2] x86/apic: fix integer overflow on 10 bit left shift of cpu_khz

[PATCH][V2] x86/apic: fix integer overflow on 10 bit left shift of cpu_khz

[Colin King]

From: Colin Ian King <colin.king@canonical.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@canonical.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.

--
2.20.1

Re: [PATCH][V2] x86/apic: fix integer overflow on 10 bit left shift of cpu_khz

[Dan Carpenter]

On Wed, Jun 19, 2019 at 07:14:46PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.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@canonical.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

[tip:x86/urgent] x86/apic: Fix integer overflow on 10 bit left shift of cpu_khz

[tip-bot for Colin Ian King]

Commit-ID:  ea136a112d89bade596314a1ae49f748902f4727
Gitweb:     https://git.kernel.org/tip/ea136a112d89bade596314a1ae49f748902f4727
Author:     Colin Ian King <colin.king@canonical.com>
AuthorDate: Wed, 19 Jun 2019 19:14:46 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 22 Jun 2019 11:59:31 +0200

x86/apic: Fix integer overflow on 10 bit left shift of cpu_khz

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, i.e. ~4.2 GHz.

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@canonical.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: kernel-janitors@vger.kernel.org
Link: https://lkml.kernel.org/r/20190619181446.13635-1-colin.king@canonical.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 177aa8ef2afa..85be316665b4 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;
+				max_loops -= ntsc - tsc;
 			} else {
 				max_loops--;
 			}