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

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 177aa8ef2afa7c6691ea64a2131ba2a3dd1b5da4..85be316665b4a38e2d650bda07db3843485a91e1 100644 (file)
--- 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--;
                        }