From: Josh Poimboeuf jpoimboe@redhat.com
commit 2700fefdb2d9751c416ad56897e27d41e409324a upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/entry/entry_64.S | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-)
--- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -853,7 +853,7 @@ ENTRY(switch_to_thread_stack) ret END(switch_to_thread_stack)
-.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
@@ -873,6 +873,20 @@ 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 @@ -1093,7 +1107,7 @@ apicinterrupt3 HYPERVISOR_CALLBACK_VECTO #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