ftrace/x86_64: Emulate call function while updating in breakpoint handler

Nicolai Stange discovered[1] that if live kernel patching is enabled, and the
function tracer started tracing the same function that was patched, the
conversion of the fentry call site during the translation of going from
calling the live kernel patch trampoline to the iterator trampoline, would
have as slight window where it didn't call anything.

As live kernel patching depends on ftrace to always call its code (to
prevent the function being traced from being called, as it will redirect
it). This small window would allow the old buggy function to be called, and
this can cause undesirable results.

Nicolai submitted new patches[2] but these were controversial. As this is
similar to the static call emulation issues that came up a while ago[3].
But after some debate[4][5] adding a gap in the stack when entering the
breakpoint handler allows for pushing the return address onto the stack to
easily emulate a call.

[1] http://lkml.kernel.org/r/[email protected]
[2] http://lkml.kernel.org/r/[email protected]
[3] http://lkml.kernel.org/r/3cf04e113d71c9f8e4be95fb84a510f085aa4afa.1541711457.git.jpoimboe@redhat.com
[4] http://lkml.kernel.org/r/CAHk-=wh5OpheSU8Em_Q3Hg8qw_JtoijxOdPtHru6d+5K8TWM=A@mail.gmail.com
[5] http://lkml.kernel.org/r/CAHk-=wjvQxY4DvPrJ6haPgAa6b906h=MwZXO6G8OtiTGe=N7_w@mail.gmail.com

[
  Live kernel patching is not implemented on x86_32, thus the emulate
  calls are only for x86_64.
]

Cc: Andy Lutomirski <[email protected]>
Cc: Nicolai Stange <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: the arch/x86 maintainers <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Miroslav Benes <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Joe Lawrence <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Mimi Zohar <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Nayna Jain <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: "open list:KERNEL SELFTEST FRAMEWORK" <[email protected]>
Cc: [email protected]
Fixes: b700e7f03df5 ("livepatch: kernel: add support for live patching")
Tested-by: Nicolai Stange <[email protected]>
Reviewed-by: Nicolai Stange <[email protected]>
Reviewed-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
[ Changed to only implement emulated calls for x86_64 ]
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

0 files changed, 0 insertions, 0 deletions