On Mon, 15 Mar 2021 21:30:03 -0500 Josh Poimboeuf <jpoim...@redhat.com> wrote:
> On Fri, Mar 12, 2021 at 03:41:44PM +0900, Masami Hiramatsu wrote: > > Hello, > > > > Here is the 2nd version of the series to fix the stacktrace with kretprobe. > > > > The 1st series is here; > > > > https://lore.kernel.org/bpf/161495873696.346821.10161501768906432924.stgit@devnote2/ > > > > In this version I merged the ORC unwinder fix for kretprobe which discussed > > in the > > previous thread. [3/10] is updated according to the Miroslav's comment. > > [4/10] is > > updated for simplify the code. [5/10]-[9/10] are discussed in the previsous > > tread > > and are introduced to the series. > > > > Daniel, can you also test this again? I and Josh discussed a bit different > > method and I've implemented it on this version. > > > > This actually changes the kretprobe behavisor a bit, now the instraction > > pointer in > > the pt_regs passed to kretprobe user handler is correctly set the real > > return > > address. So user handlers can get it via instruction_pointer() API. > > When I add WARN_ON(1) to a test kretprobe, it doesn't unwind properly. > > show_trace_log_lvl() reads the entire stack in lockstep with calls to > the unwinder so that it can decide which addresses get prefixed with > '?'. So it expects to find an actual return address on the stack. > Instead it finds %rsp. So it never syncs up with unwind_next_frame() > and shows all remaining addresses as unreliable. > > Call Trace: > __kretprobe_trampoline_handler+0xca/0x1a0 > trampoline_handler+0x3d/0x50 > kretprobe_trampoline+0x25/0x50 > ? init_test_probes.cold+0x323/0x387 > ? init_kprobes+0x144/0x14c > ? init_optprobes+0x15/0x15 > ? do_one_initcall+0x5b/0x300 > ? lock_is_held_type+0xe8/0x140 > ? kernel_init_freeable+0x174/0x2cd > ? rest_init+0x233/0x233 > ? kernel_init+0xa/0x11d > ? ret_from_fork+0x22/0x30 > > How about pushing 'kretprobe_trampoline' instead of %rsp for the return > address placeholder. That fixes the above test, and removes the need > for the weird 'state->ip == sp' check: > > Call Trace: > __kretprobe_trampoline_handler+0xca/0x150 > trampoline_handler+0x3d/0x50 > kretprobe_trampoline+0x29/0x50 > ? init_test_probes.cold+0x323/0x387 > elfcorehdr_read+0x10/0x10 > init_kprobes+0x144/0x14c > ? init_optprobes+0x15/0x15 > do_one_initcall+0x72/0x280 > kernel_init_freeable+0x174/0x2cd > ? rest_init+0x122/0x122 > kernel_init+0xa/0x10e > ret_from_fork+0x22/0x30 > > Though, init_test_probes.cold() (the real return address) is still > listed as unreliable. Maybe we need a call to kretprobe_find_ret_addr() > in show_trace_log_lvl(), similar to the ftrace_graph_ret_addr() call > there. Thanks for the test! OK, that could be acceptable. However, push %sp still needed for accessing stack address from kretprobe handler via pt_regs. (regs->sp must point the stack address) Anyway, with int3, it pushes one more entry for emulating call, so I think it is OK. Let me update the series! Thank you! > > > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > index 06f33bfebc50..70188fdd288e 100644 > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -766,19 +766,19 @@ asm( > "kretprobe_trampoline:\n" > /* We don't bother saving the ss register */ > #ifdef CONFIG_X86_64 > - " pushq %rsp\n" > + /* Push fake return address to tell the unwinder it's a kretprobe */ > + " pushq $kretprobe_trampoline\n" > UNWIND_HINT_FUNC > " pushfq\n" > SAVE_REGS_STRING > " movq %rsp, %rdi\n" > " call trampoline_handler\n" > - /* Replace saved sp with true return address. */ > + /* Replace the fake return address with the real one. */ > " movq %rax, 19*8(%rsp)\n" > RESTORE_REGS_STRING > " popfq\n" > #else > " pushl %esp\n" > - UNWIND_HINT_FUNC > " pushfl\n" > SAVE_REGS_STRING > " movl %esp, %eax\n" > diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c > index 1d1b9388a1b1..1d3de84d2410 100644 > --- a/arch/x86/kernel/unwind_orc.c > +++ b/arch/x86/kernel/unwind_orc.c > @@ -548,8 +548,7 @@ bool unwind_next_frame(struct unwind_state *state) > * In those cases, find the correct return address from > * task->kretprobe_instances list. > */ > - if (state->ip == sp || > - is_kretprobe_trampoline(state->ip)) > + if (is_kretprobe_trampoline(state->ip)) > state->ip = kretprobe_find_ret_addr(state->task, > &state->kr_iter); > > > -- Masami Hiramatsu <mhira...@kernel.org>
