linux-kernel - [PATCH 3.16 74/87] x86/apic: Fix integer overflow on 10 bit left shift of cpu

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Date:   Wed, 02 Oct 2019 20:06:51 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        kernel-janitors@...r.kernel.org, "Borislav Petkov" <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Colin Ian King" <colin.king@...onical.com>
Subject: [PATCH 3.16 74/87] x86/apic: Fix integer overflow on 10 bit left
 shift of cpu_khz

3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

commit ea136a112d89bade596314a1ae49f748902f4727 upstream.

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
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kernel/apic/apic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1403,7 +1403,8 @@ void setup_local_APIC(void)
 		if (queued) {
 			if (cpu_has_tsc && cpu_khz) {
 				rdtscll(ntsc);
-				max_loops = (cpu_khz << 10) - (ntsc - tsc);
+				max_loops = (long long)cpu_khz << 10;
+				max_loops -= ntsc - tsc;
 			} else
 				max_loops--;
 		}