On Tue, May 07, 2019 at 01:42:28PM -0400, Steven Rostedt wrote: > From: Josh Poimboeuf <[email protected]> > > To allow an int3 handler to emulate a call instruction, it must be able to > push a return address onto the stack. Add a gap to the stack to allow the > int3 handler to push the return address and change the return from int3 to > jump straight to the emulated called function target. > > Link: http://lkml.kernel.org/r/20181130183917.hxmti5josgq4clti@treble > Link: > http://lkml.kernel.org/r/[email protected] > > [ > Note, this is needed to allow Live Kernel Patching to not miss calling a > patched function when tracing is enabled. -- Steven Rostedt > ] > > Cc: [email protected] > Fixes: b700e7f03df5 ("livepatch: kernel: add support for live patching") > Signed-off-by: Josh Poimboeuf <[email protected]> > Signed-off-by: Steven Rostedt (VMware) <[email protected]> > --- > arch/x86/entry/entry_64.S | 18 ++++++++++++++++-- > 1 file changed, 16 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > index 1f0efdb7b629..00df6b135ab1 100644 > --- a/arch/x86/entry/entry_64.S > +++ b/arch/x86/entry/entry_64.S > @@ -879,7 +879,7 @@ apicinterrupt IRQ_WORK_VECTOR > irq_work_interrupt smp_irq_work_interrupt > * @paranoid == 2 is special: the stub will never switch stacks. This is for > * #DF: if the thread stack is somehow unusable, we'll still get a useful > OOPS. > */ > -.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 > +.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 > create_gap=0 > ENTRY(\sym) > UNWIND_HINT_IRET_REGS offset=\has_error_code*8 > > @@ -899,6 +899,20 @@ ENTRY(\sym) > jnz .Lfrom_usermode_switch_stack_\@ > .endif > > + .if \create_gap == 1 > + /* > + * If coming from kernel space, create a 6-word gap to allow the static > + * call #BP handler to emulate a call instruction.
Might as well refer to it as the int3 handler, since that's what the rest of the code calls it. Also, no static calls yet :-) So: s/static call #BP handler/int3 handler/ -- Josh
