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") 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 --- 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..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 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