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Subject[PATCH v3] KVM: X86: Fix load RFLAGS w/o the fixed bit
Date
From: Wanpeng Li <wanpeng.li@hotmail.com>

*** 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.

Suggested-by: Jim Mattson <jmattson@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
v2 -> v3:
* move Oring X86_EFLAGS_FIXED to kvm_arch_vcpu_ioctl_set_regs
v1 -> v2:
* Oring X86_EFLAGS_FIXED

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 ebe0a3a..0c5d55c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7405,7 +7405,7 @@ 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;

--
2.7.4
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