On Thu, 26 Jul 2018 12:40:28 +0200 Nicolai Stange <nstange@xxxxxxx> wrote: > Hi, > > if a user starts to trace a live patched function, its mcount call will get > redirected from a trampoline to ftrace_regs_caller. > > In preparation for that, ftrace on x86 first installs an int3 insn at that > call site. > > ftrace_int3_handler() in turn simply skips over the mcount call insn, > effectively reverting the livepatch for that function during > ftrace_replace_code(). > > This breaks KLP's consistency model. > > > There are two possible options for fixing this: > 1.) At the ftrace level. > 2.) Search for a matching klp_ops from ftrace_int3_handler() and > handle the redirection if needed. > > Both have their drawbacks, hence the RFC mode for this patch implementing > 1.). > > The main disadvantage is that it doesn't work on 32 bits (c.f. the patch > description), but for KLP this would be fine. > > OTOH, it keeps KLP specific code out of ftrace_int3_handler() and might > perhaps be beneficial in other contexts as well. > > Thanks for your comments! Thanks, I need to revisit this code. I have ideas that would fix this problem and improve the live patching code generally. I'm hoping to get to this within the next month. -- Steve > > Nicolai > > Nicolai Stange (1): > x86/ftrace: make ftrace_int3_handler() not to skip fops invocation > > arch/x86/kernel/ftrace.c | 48 ++++++++++++++++++++++++++++++++------ > arch/x86/kernel/ftrace_64.S | 56 +++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 97 insertions(+), 7 deletions(-) > -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
