linux-kernel - [PATCH] kvm: x86: use getboottime64

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Message-Id: <20160617154914.660326-1-arnd@arndb.de>
Date:	Fri, 17 Jun 2016 17:48:56 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:	y2038@...ts.linaro.org, Arnd Bergmann <arnd@...db.de>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Andrey Smetanin <asmetanin@...tuozzo.com>,
	"Denis V. Lunev" <den@...nvz.org>,
	Haozhong Zhang <haozhong.zhang@...el.com>,
	Feng Wu <feng.wu@...el.com>,
	Steve Rutherford <srutherford@...gle.com>,
	Andy Lutomirski <luto@...nel.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] kvm: x86: use getboottime64

KVM reads the current boottime value as a struct timespec in order to
calculate the guest wallclock time, resulting in an overflow in 2038
on 32-bit systems.

The data then gets passed as an unsigned 32-bit number to the guest,
and that in turn overflows in 2106.

We cannot do much about the second overflow, which affects both 32-bit
and 64-bit hosts, but we can ensure that they both behave the same
way and don't overflow until 2106, by using getboottime64() to read
a timespec64 value.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/x86/kvm/x86.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 53241618e3c9..f79c86510408 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1163,7 +1163,7 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
 	int version;
 	int r;
 	struct pvclock_wall_clock wc;
-	struct timespec boot;
+	struct timespec64 boot;
 
 	if (!wall_clock)
 		return;
@@ -1186,13 +1186,13 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
 	 * wall clock specified here.  guest system time equals host
 	 * system time for us, thus we must fill in host boot time here.
 	 */
-	getboottime(&boot);
+	getboottime64(&boot);
 
 	if (kvm->arch.kvmclock_offset) {
-		struct timespec ts = ns_to_timespec(kvm->arch.kvmclock_offset);
-		boot = timespec_sub(boot, ts);
+		struct timespec64 ts = ns_to_timespec64(kvm->arch.kvmclock_offset);
+		boot = timespec64_sub(boot, ts);
 	}
-	wc.sec = boot.tv_sec;
+	wc.sec = (u32)boot.tv_sec; /* overflow in 2106 guest time */
 	wc.nsec = boot.tv_nsec;
 	wc.version = version;
 
-- 
2.9.0