On Tue, May 07, 2019 at 01:42:28PM -0400, Steven Rostedt wrote:
From: Josh Poimboeuf jpoimboe@redhat.com
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/20190502162133.GX2623@hirez.programming.kicks-ass.n...
[ Note, this is needed to allow Live Kernel Patching to not miss calling a patched function when tracing is enabled. -- Steven Rostedt ]
Cc: stable@vger.kernel.org Fixes: b700e7f03df5 ("livepatch: kernel: add support for live patching") Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org
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/