linux-kernel - [PATCH AUTOSEL 4.19 08/26] x86/apic: Fix integer overflow on 10 bit left shift of cpu

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Date:   Tue,  2 Jul 2019 22:16:07 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Colin Ian King <colin.king@...onical.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, kernel-janitors@...r.kernel.org,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.19 08/26] x86/apic: Fix integer overflow on 10 bit left shift of cpu_khz

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

[ Upstream commit ea136a112d89bade596314a1ae49f748902f4727 ]

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@...onical.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: kernel-janitors@...r.kernel.org
Link: https://lkml.kernel.org/r/20190619181446.13635-1-colin.king@canonical.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 84132eddb5a8..2646234380cc 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1452,7 +1452,8 @@ 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--;
 			}
-- 
2.20.1