Patch "KVM: X86: Fix load RFLAGS w/o the fixed bit" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

KVM: X86: Fix load RFLAGS w/o the fixed bit

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     kvm-x86-fix-load-rflags-w-o-the-fixed-bit.patch

and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Wanpeng Li <[email protected]>
Date: Thu, 7 Dec 2017 00:30:08 -0800
Subject: KVM: X86: Fix load RFLAGS w/o the fixed bit
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From: Wanpeng Li <[email protected]>

commit d73235d17ba63b53dc0e1051dbc10a1f1be91b71 upstream.

*** 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.

---
 arch/x86/kvm/x86.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -7132,7 +7132,7 @@ int kvm_arch_vcpu_ioctl_set_regs(struct
 #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;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/kvm-x86-fix-load-rflags-w-o-the-fixed-bit.patch