[Bug 65561] KVM:Entry failed on Single stepping sti instruction

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=65561

--- Comment #20 from Jidong Xiao <jidong.xiao@gmail.com> ---
Thanks Jatin, I actually tried some other instructions, like accessing cr
register. I use the following program:

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

main(){

        asm __volatile__ (
                "mov %cr0, %eax\n"
                "mov %cr3, %ebx\n"
        );
        printf("test cr\n");
}

In x86_emulate_insn(), there is a piece of code like this (the printk is added
by me.)
==================================
        case 0x20: /* mov cr, reg */
                printk(KERN_ERR "DEBUG: Passed %s %d
\n",__FUNCTION__,__LINE__);
                if (c->modrm_mod != 3)
                        goto cannot_emulate;
                c->regs[c->modrm_rm] =
                                realmode_get_cr(ctxt->vcpu, c->modrm_reg);
                c->dst.type = OP_NONE;  /* no writeback */
                break;
==================================
My results show that the above c program does not trigger this printk statement
neither. I assume accessing cr should be a privileged operation, right? So I am
really curious that how to trigger these printk statements?

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