[added to the 4.1 stable tree] KVM: X86: Fix load RFLAGS w/o the fixed bit

[Sasha Levin <Alexander.Levin@xxxxxxxxxxxxx>]

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

This patch has been added to the 4.1 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit d73235d17ba63b53dc0e1051dbc10a1f1be91b71 ]

 *** Guest State ***
 CR0: actual=0x0000000000000030, shadow=0x0000000060000010, gh_mask=fffffffffffffff7
 CR4: actual=0x0000000000002050, shadow=0x0000000000000000, gh_mask=ffffffffffffe871
 CR3 = 0x00000000fffbc000
 RSP = 0x0000000000000000  RIP = 0x0000000000000000
 RFLAGS=0x00000000         DR7 = 0x0000000000000400
        ^^^^^^^^^^

The failed vmentry is triggered by the following testcase when ept=Y:

    #include <unistd.h>
    #include <sys/syscall.h>
    #include <string.h>
    #include <stdint.h>
    #include <linux/kvm.h>
    #include <fcntl.h>
    #include <sys/ioctl.h>

    long r[5];
    int main()
    {
    	r[2] = open("/dev/kvm", O_RDONLY);
    	r[3] = ioctl(r[2], KVM_CREATE_VM, 0);
    	r[4] = ioctl(r[3], KVM_CREATE_VCPU, 7);
    	struct kvm_regs regs = {
    		.rflags = 0,
    	};
    	ioctl(r[4], KVM_SET_REGS, &regs);
    	ioctl(r[4], KVM_RUN, 0);
    }

X86 RFLAGS bit 1 is fixed set, userspace can simply clearing bit 1
of RFLAGS with KVM_SET_REGS ioctl which results in vmentry fails.
This patch fixes it by oring X86_EFLAGS_FIXED during ioctl.

Cc: stable@xxxxxxxxxxxxxxx
Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Quan Xu <quan.xu0@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Cc: Jim Mattson <jmattson@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7840d42734a1..bd23b1cad80a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6737,7 +6737,7 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 #endif
 
 	kvm_rip_write(vcpu, regs->rip);
-	kvm_set_rflags(vcpu, regs->rflags);
+	kvm_set_rflags(vcpu, regs->rflags | X86_EFLAGS_FIXED);
 
 	vcpu->arch.exception.pending = false;
 
-- 
2.14.1