From: Peter Zijlstra
> Sent: 07 May 2019 09:58
...
> + /*
> + * When we're here from kernel mode; the (exception) stack looks like:
> + *
> + * 4*4(%esp) - <previous context>
> + * 3*4(%esp) - flags
> + * 2*4(%esp) - cs
> + * 1*4(%esp) - ip
> + * 0*4(%esp) - orig_eax
Am I right in thinking that this is the only 'INT3' stack frame that
needs to be 'fiddled' with?
And that the 'emulate a call instruction' has verified that is the case??
So the %cs is always the kernel %cs.
If the 'call target' address is saved in a per-cpu location it ought
to be possible to get the code that returns from the INT3 with the
call target address (or zero) in %ax.
If non-zero, instead of 'pop %ax; iret' execute:
xchg %eax, 4(%esp) - swap function address and callers ip
push 12(%esp) - old flags
mov 14(%esp),%eax - callers address over flags
popf - enables interrupts (etc)
pop %eax
retf - Jump to called function and remove %cs
Nothing else needs to be moved.
David
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