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x86_64: Add gap to int3 to allow for call emulation

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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: b700e7f03d ("livepatch: kernel: add support for live patching")
Tested-by: Nicolai Stange <nstange@suse.de>
Reviewed-by: Nicolai Stange <nstange@suse.de>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Josh Poimboeuf 2018-11-30 12:39:17 -06:00 committed by Steven Rostedt (VMware)
parent 03197fc02b
commit 2700fefdb2
1 changed files with 16 additions and 2 deletions
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18
arch/x86/entry/entry_64.S
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@ -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