Hi Josh, On Mon, 8 Mar 2021 19:19:45 -0600 Josh Poimboeuf <jpoim...@redhat.com> wrote:
> On Mon, Mar 08, 2021 at 11:52:10AM +0900, Masami Hiramatsu wrote: > > So at the kretprobe handler, we have 2 issues. > > 1) the return address (caller_func+0x15) is not on the stack. > > this can be solved by searching from current->kretprobe_instances. > > 2) the stack frame size of kretprobe_trampoline is unknown > > Since the stackframe is fixed, the fixed number (0x98) can be used. > > > > However, those solutions are only for the kretprobe handler. The stacktrace > > from interrupt handler hit in the kretprobe_trampoline still doesn't work. > > > > So, here is my idea; > > > > 1) Change the trampline code to prepare stack frame at first and save > > registers on it, instead of "push". This will makes ORC easy to setup > > stackframe information for this code. > > 2) change the return addres fixup timing. Instead of using return value > > of trampoline handler, before removing the real return address from > > current->kretprobe_instances. > > 3) Then, if orc_find() finds the ip is in the kretprobe_trampoline, it > > checks the contents of the end of stackframe (at the place of regs->sp) > > is same as the address of it. If it is, it can find the correct address > > from current->kretprobe_instances. If not, there is a correct address. > > > > I need to find how the ORC info is prepared for 1), maybe UNWIND_HINT macro > > may help? > > Hi Masami, > > If I understand correctly, for #1 you need an unwind hint which treats > the instruction *after* the "pushq %rsp" as the beginning of the > function. Thanks for the patch. In that case, should I still change the stack allocation? Or can I continue to use a series of "push/pop" ? > > I'm thinking this should work: OK, Let me test it. Thanks! > > > diff --git a/arch/x86/include/asm/unwind_hints.h > b/arch/x86/include/asm/unwind_hints.h > index 8e574c0afef8..8b33674288ea 100644 > --- a/arch/x86/include/asm/unwind_hints.h > +++ b/arch/x86/include/asm/unwind_hints.h > @@ -52,6 +52,11 @@ > UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=8 type=UNWIND_HINT_TYPE_FUNC > .endm > > +#else > + > +#define UNWIND_HINT_FUNC \ > + UNWIND_HINT(ORC_REG_SP, 8, UNWIND_HINT_TYPE_FUNC, 0) > + > #endif /* __ASSEMBLY__ */ > > #endif /* _ASM_X86_UNWIND_HINTS_H */ > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > index df776cdca327..38ff1387f95d 100644 > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -767,6 +767,7 @@ asm( > /* We don't bother saving the ss register */ > #ifdef CONFIG_X86_64 > " pushq %rsp\n" > + UNWIND_HINT_FUNC > " pushfq\n" > SAVE_REGS_STRING > " movq %rsp, %rdi\n" > @@ -790,7 +791,6 @@ asm( > ".size kretprobe_trampoline, .-kretprobe_trampoline\n" > ); > NOKPROBE_SYMBOL(kretprobe_trampoline); > -STACK_FRAME_NON_STANDARD(kretprobe_trampoline); > > > /* > -- Masami Hiramatsu <mhira...@kernel.org>
