Re: [PATCH kernel] KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM_GUEST

[Fabiano Rosas <farosas@linux.ibm.com>]

Alexey Kardashevskiy <aik@ozlabs.ru> writes:

> H_COPY_TOFROM_GUEST is an hcall for an upper level VM to access its nested
> VMs memory. The userspace can trigger WARN_ON_ONCE(!(gfp & __GFP_NOWARN))
> in __alloc_pages() by constructing a tiny VM which only does
> H_COPY_TOFROM_GUEST with a too big GPR9 (number of bytes to copy).
>
> This silences the warning by adding __GFP_NOWARN.
>
> Spotted by syzkaller.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---

Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>

>  arch/powerpc/kvm/book3s_hv_nested.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
> index e57c08b968c0..a2e34efb8d31 100644
> --- a/arch/powerpc/kvm/book3s_hv_nested.c
> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
> @@ -580,7 +580,7 @@ long kvmhv_copy_tofrom_guest_nested(struct kvm_vcpu *vcpu)
>  	if (eaddr & (0xFFFUL << 52))
>  		return H_PARAMETER;
>
> -	buf = kzalloc(n, GFP_KERNEL);
> +	buf = kzalloc(n, GFP_KERNEL | __GFP_NOWARN);
>  	if (!buf)
>  		return H_NO_MEM;