Re: [PATCH 4.19 STABLE 2/2] KVM: VMX: Mark RCX, RDX and RSI as clobbered in vmx_vcpu_run()'s asm blob

Greg Kroah-Hartman
2020-05-05T06:15:07Z

On Mon, May 04, 2020 at 06:23:48PM -0700, Sean Christopherson wrote:
> Save RCX, RDX and RSI to fake outputs to coerce the compiler into
> treating them as clobbered. RCX in particular is likely to be reused by
> the compiler to dereference the 'struct vcpu_vmx' pointer, which will
> result in a null pointer dereference now that RCX is zeroed by the asm
> blob.
>
> Add ASM_CALL_CONSTRAINT to fudge around an issue where <something>
> during modpost can't find vmx_return when specifying output constraints.
>
> Reported-by: Tobias Urdin <tobias.urdin@binero.com>
> Fixes: b4be98039a92 ("KVM: VMX: Zero out *all* general purpose registers after VM-Exit")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/vmx.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 5b06a98ffd4c..54c8b4dc750d 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -10882,7 +10882,8 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
> ".global vmx_return \n\t"
> "vmx_return: " _ASM_PTR " 2b \n\t"
> ".popsection"
> - : : "c"(vmx), "d"((unsigned long)HOST_RSP), "S"(evmcs_rsp),
> + : ASM_CALL_CONSTRAINT, "=c"((int){0}), "=d"((int){0}), "=S"((int){0})
> + : "c"(vmx), "d"((unsigned long)HOST_RSP), "S"(evmcs_rsp),
> [launched]"i"(offsetof(struct vcpu_vmx, __launched)),
> [fail]"i"(offsetof(struct vcpu_vmx, fail)),
> [host_rsp]"i"(offsetof(struct vcpu_vmx, host_rsp)),
> --
> 2.26.0
>

What is the git commit id of this patch in Linus's tree?

thanks,

greg k-h