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

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Message-Id: <20190619181325.13574-1-colin.king@canonical.com>
Date:   Wed, 19 Jun 2019 19:13:25 +0100
From:   Colin King <colin.king@...onical.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/apic: fix integer overflow on 10 bit right shift of cpu_khz

From: Colin Ian King <colin.king@...onical.com>

The right 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--;
 			}
-- 
2.20.1