Re: [PATCH] kvm: fix poison overwritten caused by using wrong xstate size

[Sheng Yang <sheng@linux.intel.com>]

On Friday 13 August 2010 15:19:11 Xiaotian Feng wrote:
> fpu.state is allocated from task_xstate_cachep, the size of
> task_xstate_cachep is xstate_size. xstate_size is set from cpuid
> instruction, which is often smaller than sizeof(struct xsave_struct). kvm
> is using sizeof(struct xsave_struct) to fill in/out fpu.state.xsave, as
> what we allocated for fpu.state is xstate_size, kernel will write out of
> memory and caused poison/redzone/padding overwritten warnings.
>
> Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Suresh Siddha <suresh.b.siddha@intel.com>
> Cc: Brian Gerst <brgerst@gmail.com>
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Robert Richter <robert.richter@amd.com>
> Cc: Sheng Yang <sheng@linux.intel.com>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Cc: Gleb Natapov <gleb@redhat.com>
> Cc: Jan Kiszka <jan.kiszka@siemens.com>
 
Reviewed-by: Sheng Yang <sheng@linux.intel.com>

--
regards
Yang, Sheng

> ---
>  arch/x86/kernel/i387.c |    1 +
>  arch/x86/kvm/x86.c     |    4 ++--
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
> index 1f11f5c..a46cb35 100644
> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -40,6 +40,7 @@
> 
>  static unsigned int		mxcsr_feature_mask __read_mostly = 0xffffffffu;
>  unsigned int xstate_size;
> +EXPORT_SYMBOL_GPL(xstate_size);
>  unsigned int sig_xstate_ia32_size = sizeof(struct _fpstate_ia32);
>  static struct i387_fxsave_struct fx_scratch __cpuinitdata;
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 25f1907..3a09c62 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2387,7 +2387,7 @@ static void kvm_vcpu_ioctl_x86_get_xsave(struct
> kvm_vcpu *vcpu, if (cpu_has_xsave)
>  		memcpy(guest_xsave->region,
>  			&vcpu->arch.guest_fpu.state->xsave,
> -			sizeof(struct xsave_struct));
> +			xstate_size);
>  	else {
>  		memcpy(guest_xsave->region,
>  			&vcpu->arch.guest_fpu.state->fxsave,
> @@ -2405,7 +2405,7 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct
> kvm_vcpu *vcpu,
> 
>  	if (cpu_has_xsave)
>  		memcpy(&vcpu->arch.guest_fpu.state->xsave,
> -			guest_xsave->region, sizeof(struct xsave_struct));
> +			guest_xsave->region, xstate_size);
>  	else {
>  		if (xstate_bv & ~XSTATE_FPSSE)
>  			return -EINVAL;