On Thu, 2 May 2019 13:49:29 -0700 Linus Torvalds torvalds@linux-foundation.org wrote:
On Thu, May 2, 2019 at 1:22 PM Peter Zijlstra peterz@infradead.org wrote:
Something like so; it boots; but I could've made some horrible mistake (again).
This actually looks much better to me.
Maybe it's more lines (I didn't check), but it's a lot simpler in that now the magic of the int3 stack doesn't get exposed to anything else.
We *could* also make this kernel-mode-only do_int3() be a special function, and do something like
# args: pt_regs pointer (no error code for int3) movl %esp,%eax # allocate a bit of extra room on the stack, so that'kernel_int3' can move the pt_regs subl $8,%esp call kernel_int3 movl %eax,%esp
and not do any stack switching magic in the asm code AT ALL. We'd do
struct pt_regs *kernel_int3(struct pt_regs *regs) { .. return regs; }and now you the rule for call emulation ends up being that you need to "memmove()" the ptregs up and down properly, and return the new pt_regs pointer.
Hmm? That would simplify the asm code further, but some people might find it objectionable?
The problem with this approach is that it would require doing the same for x86_64, as the int3 C code is the same for both. And that may be a bit more difficult on the x86_64 side because it's all done with a simple flag in the idtentry macro to add the gap.
-- Steve