Commit 2700fefd authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Steven Rostedt (VMware)
Browse files

x86_64: Add gap to int3 to allow for call emulation 

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.net



[
  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: b700e7f0 ("livepatch: kernel: add support for live patching")
Tested-by: default avatarNicolai Stange <nstange@suse.de>
Reviewed-by: default avatarNicolai Stange <nstange@suse.de>
Reviewed-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 03197fc0

arch/x86/entry/entry_64.S

+16 −2
Original line number Diff line number Diff line
@@ -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

	 * int3 handler to emulate a call instruction.

	 */

	testb	$3, CS-ORIG_RAX(%rsp)

	jnz	.Lfrom_usermode_no_gap_\@

	.rept	6

	pushq	5*8(%rsp)

	.endr

	UNWIND_HINT_IRET_REGS offset=8

.Lfrom_usermode_no_gap_\@:

	.endif



	.if \paranoid

	call	paranoid_entry

	.else
@@ -1130,7 +1144,7 @@ apicinterrupt3 HYPERV_STIMER0_VECTOR \ 
#endif /* CONFIG_HYPERV */



idtentry debug			do_debug		has_error_code=0	paranoid=1 shift_ist=DEBUG_STACK

idtentry int3			do_int3			has_error_code=0

idtentry int3			do_int3			has_error_code=0	create_gap=1

idtentry stack_segment		do_stack_segment	has_error_code=1



#ifdef CONFIG_XEN_PV

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