Messages in this thread | | | Date | Wed, 15 Mar 2006 01:09:35 -0800 | From | Chris Wright <> | Subject | Re: [RFC, PATCH 7/24] i386 Vmi memory hole |
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* Zachary Amsden (zach@vmware.com) wrote: > ENTRY(sysenter_entry) > movl TSS_sysenter_esp0(%esp),%esp > sysenter_past_esp: > STI > pushl $(__USER_DS) > pushl %ebp > pushfl > pushl $(__USER_CS) > pushl $SYSENTER_RETURN > > SYSENTER_RETURN is a link time constant that is defined based on the > location of the vsyscall page. If the vsyscall page can move, this can > not be a constant. The reason is, this "fake" exception frame is used > to return back to the EIP of the call site, and sysenter does not record > the EIP of the call site.
It's only real issue for something like execshield. For this it's easy to do the fixed math since it's still at fixed address.
+ DEFINE(VSYSCALL_BASE, (PAGE_OFFSET - 2*PAGE_SIZE));
But execshield has to make SYSENTER_RETURN context sensitive to current since the vdso is mapped at random location.
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