From mboxrd@z Thu Jan  1 00:00:00 1970
From: bugzilla-daemon@bugzilla.kernel.org
Subject: [Bug 65561] KVM:Entry failed on Single stepping sti instruction
Date: Sat, 24 May 2014 05:46:44 +0000
Message-ID: <bug-65561-28872-MPJyby2wuf@https.bugzilla.kernel.org/>
References: <bug-65561-28872@https.bugzilla.kernel.org/>
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https://bugzilla.kernel.org/show_bug.cgi?id=65561

--- Comment #22 from Jidong Xiao <jidong.xiao@gmail.com> ---
Alright, I added a printk statement in the wrmsr case, like this:

        case 0x30:
                printk(KERN_ERR "DEBUG: Passed %s %d
\n",__FUNCTION__,__LINE__);
                /* wrmsr */
                msr_data = (u32)c->regs[VCPU_REGS_RAX]
                        | ((u64)c->regs[VCPU_REGS_RDX] << 32);
                rc = kvm_set_msr(ctxt->vcpu, c->regs[VCPU_REGS_RCX], msr_data);
                if (rc) {
                        kvm_inject_gp(ctxt->vcpu, 0);
                        c->eip = kvm_rip_read(ctxt->vcpu);
                }
                rc = X86EMUL_CONTINUE;
                c->dst.type = OP_NONE;
                break;

And i run a c program to access msr, like this:

linux:~/code/cvedr # cat accessmsr.c
#include <stdio.h>

main(){
        asm volatile("wrmsr");
        printf("test msr\n");
}

linux:~/code/cvedr # ./accessmsr
Segmentation fault

Even though my c program in the guest os got a segmentation fault, from the
host os level, I don't see the printk statement is triggered, so this is not
about privileged instructions or unprivileged instructions. I think there must
be some other conditions to trigger these printk statements.

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