[1/3] x86_64: Add gap to int3 to allow for call emulation
diff mbox series

Message ID 20190508020000.433743991@goodmis.org
State Mainlined
Commit 2700fefdb2d9751c416ad56897e27d41e409324a
Headers show
  • x86_64/ftrace: Emulate calls from int3 when patching functions
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Commit Message

Steven Rostedt May 8, 2019, 1:56 a.m. UTC
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.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: 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 mbox series

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 1f0efdb7b629..27fcc6fbdd52 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
 	UNWIND_HINT_IRET_REGS offset=\has_error_code*8
@@ -899,6 +899,20 @@  ENTRY(\sym)
 	jnz	.Lfrom_usermode_switch_stack_\@
+	.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
+	.endif
 	.if \paranoid
 	call	paranoid_entry
@@ -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