On 12/14/2010 12:48 AM, Avi Kivity wrote:
On 12/13/2010 07:17 PM, Hollis Blanchard wrote:
Rewriting is dangerous if the guest is unaware of it. As soon as it
is made aware of it, it might as well actually do it in the best way
that suits it.
Can you list some examples of dangerous scenarios?
Perhaps I should rephrase... any real-world dangerous scenarios? :) I
was hoping you could share some traps you've hit with Linux or Windows
on x86.
- guest checksums own kernel pages
For runtime intrusion detection? Such guests can simply not ask the
hypervisor to enable the rewriting feature.
- clever compiler reuses code for constant pool
Not sure what you mean here. Anyways I think clever compilers are
irrelevant, since a compiler will not ordinarily emit a supervisor-mode
instruction. The hypervisor has no need to patch normal user-mode
instructions.
- guest patches itself (a la linux alternatives), surprised when it
sees a different instruction
PowerPC Linux does patch itself, which is a write-only operation.
- guest jits own kernel code (like Singularity), gets confused when it
reads back something it didn't write
This is getting really hypothetical, but why would a JIT need to read
the generated code?
Hollis Blanchard
Mentor Graphics, Embedded Systems Division
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