[Qemu-devel] [Bug 629791] Re: sysret sets invalid ss

[dascandy]

Minor update, I found that I made a mistake with the value in STAR. I
loaded 0x18 into the top 16 bits, so the bug is not that SS is 0x20
(which I thought to be wrong but was my own mistake). Why does it set
CS=0x2b from that value & run?

-- 
sysret sets invalid ss
https://bugs.launchpad.net/bugs/629791
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Status in QEMU: New

Bug description:
I'm developing an OS. I use only sysret to enter user space. When an interrupt 
occurred, it would GPF on iretq'ing from it. On investigating, the cs on the 
stack is 0x2b (valid and correct). The ss on the stack is 0x20, which has a rpl 
of 0 which is incorrect. iretq checks that and gpf's. Making the irq handler 
manually modify it to 0x23 fixes it locally.

This happens on the non-kvm'ed qemu. I haven't tried the kvm'ed one. Qemu 
version 0.12.5. I haven't tried with the current development version either.