[PATCH] kvm: x86: use getboottime64

[PATCH] kvm: x86: use getboottime64

[Arnd Bergmann]

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@arndb.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

Re: [PATCH] kvm: x86: use getboottime64

[Paolo Bonzini]

On 17/06/2016 17:48, Arnd Bergmann wrote:
> 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@arndb.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;
>  
> 

Queued, thanks.

Paolo