| Message ID | 161615655969.306069.4545805781593088526.stgit@devnote2 (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | kprobes: Fix stacktrace with kretprobes on x86 | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Fri, 19 Mar 2021 21:22:39 +0900 Masami Hiramatsu <mhiramat@kernel.org> wrote: > From: Josh Poimboeuf <jpoimboe@redhat.com> > > Add UNWIND_HINT_FUNC on kretporbe_trampoline code so that ORC > information is generated on the kretprobe_trampoline correctly. > Test bot also found a new warning for this. > >> arch/x86/kernel/kprobes/core.o: warning: objtool: kretprobe_trampoline()+0x25: call without frame pointer save/setup With CONFIG_FRAME_POINTER=y. Of course this can be fixed with additional "push %bp; mov %sp, %bp" before calling trampoline_handler. But actually we know that this function has a bit special stack frame too. Can I recover STACK_FRAME_NON_STANDARD(kretprobe_trampoline) when CONFIG_FRAME_POINTER=y ? Thank you, > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > --- > [MH] Add patch description. > --- > arch/x86/include/asm/unwind_hints.h | 5 +++++ > arch/x86/kernel/kprobes/core.c | 3 ++- > 2 files changed, 7 insertions(+), 1 deletion(-) > > 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 427d648fffcd..b31058a152b6 100644 > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -772,6 +772,7 @@ 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" > @@ -782,6 +783,7 @@ asm( > " popfq\n" > #else > " pushl %esp\n" > + UNWIND_HINT_FUNC > " pushfl\n" > SAVE_REGS_STRING > " movl %esp, %eax\n" > @@ -795,7 +797,6 @@ asm( > ".size kretprobe_trampoline, .-kretprobe_trampoline\n" > ); > NOKPROBE_SYMBOL(kretprobe_trampoline); > -STACK_FRAME_NON_STANDARD(kretprobe_trampoline); > > > /* >
On Sat, 20 Mar 2021 21:16:16 +0900 Masami Hiramatsu <mhiramat@kernel.org> wrote: > On Fri, 19 Mar 2021 21:22:39 +0900 > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > From: Josh Poimboeuf <jpoimboe@redhat.com> > > > > Add UNWIND_HINT_FUNC on kretporbe_trampoline code so that ORC > > information is generated on the kretprobe_trampoline correctly. > > > > Test bot also found a new warning for this. > > > >> arch/x86/kernel/kprobes/core.o: warning: objtool: kretprobe_trampoline()+0x25: call without frame pointer save/setup > > With CONFIG_FRAME_POINTER=y. > > Of course this can be fixed with additional "push %bp; mov %sp, %bp" before calling > trampoline_handler. But actually we know that this function has a bit special > stack frame too. > > Can I recover STACK_FRAME_NON_STANDARD(kretprobe_trampoline) when CONFIG_FRAME_POINTER=y ? So something like this. Does it work? diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c index b31058a152b6..651f337dc880 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -760,6 +760,10 @@ int kprobe_int3_handler(struct pt_regs *regs) } NOKPROBE_SYMBOL(kprobe_int3_handler); +#ifdef CONFIG_FRAME_POINTER +#undef UNWIND_HINT_FUNC +#define UNWIND_HINT_FUNC +#endif /* * When a retprobed function returns, this code saves registers and * calls trampoline_handler() runs, which calls the kretprobe's handler. @@ -797,7 +801,14 @@ asm( ".size kretprobe_trampoline, .-kretprobe_trampoline\n" ); NOKPROBE_SYMBOL(kretprobe_trampoline); - +#ifdef CONFIG_FRAME_POINTER +/* + * kretprobe_trampoline skips updating frame pointer. The frame pointer + * saved in trampoline_handler points to the real caller function's + * frame pointer. + */ +STACK_FRAME_NON_STANDARD(kretprobe_trampoline); +#endif /* * Called from kretprobe_trampoline
On Sat, Mar 20, 2021 at 09:16:16PM +0900, Masami Hiramatsu wrote: > On Fri, 19 Mar 2021 21:22:39 +0900 > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > From: Josh Poimboeuf <jpoimboe@redhat.com> > > > > Add UNWIND_HINT_FUNC on kretporbe_trampoline code so that ORC > > information is generated on the kretprobe_trampoline correctly. > > > > Test bot also found a new warning for this. > > > >> arch/x86/kernel/kprobes/core.o: warning: objtool: kretprobe_trampoline()+0x25: call without frame pointer save/setup > > With CONFIG_FRAME_POINTER=y. > > Of course this can be fixed with additional "push %bp; mov %sp, %bp" before calling > trampoline_handler. But actually we know that this function has a bit special > stack frame too. > > Can I recover STACK_FRAME_NON_STANDARD(kretprobe_trampoline) when CONFIG_FRAME_POINTER=y ? Yes, that's what I'd recommend.
On Sat, Mar 20, 2021 at 10:05:43PM +0900, Masami Hiramatsu wrote: > On Sat, 20 Mar 2021 21:16:16 +0900 > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > On Fri, 19 Mar 2021 21:22:39 +0900 > > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > > > From: Josh Poimboeuf <jpoimboe@redhat.com> > > > > > > Add UNWIND_HINT_FUNC on kretporbe_trampoline code so that ORC > > > information is generated on the kretprobe_trampoline correctly. > > > > > > > Test bot also found a new warning for this. > > > > > >> arch/x86/kernel/kprobes/core.o: warning: objtool: kretprobe_trampoline()+0x25: call without frame pointer save/setup > > > > With CONFIG_FRAME_POINTER=y. > > > > Of course this can be fixed with additional "push %bp; mov %sp, %bp" before calling > > trampoline_handler. But actually we know that this function has a bit special > > stack frame too. > > > > Can I recover STACK_FRAME_NON_STANDARD(kretprobe_trampoline) when CONFIG_FRAME_POINTER=y ? > > So something like this. Does it work? > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > index b31058a152b6..651f337dc880 100644 > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -760,6 +760,10 @@ int kprobe_int3_handler(struct pt_regs *regs) > } > NOKPROBE_SYMBOL(kprobe_int3_handler); > > +#ifdef CONFIG_FRAME_POINTER > +#undef UNWIND_HINT_FUNC > +#define UNWIND_HINT_FUNC > +#endif This hunk isn't necessary. The unwind hints don't actually have an effect with frame pointers. > /* > * When a retprobed function returns, this code saves registers and > * calls trampoline_handler() runs, which calls the kretprobe's handler. > @@ -797,7 +801,14 @@ asm( > ".size kretprobe_trampoline, .-kretprobe_trampoline\n" > ); > NOKPROBE_SYMBOL(kretprobe_trampoline); > - > +#ifdef CONFIG_FRAME_POINTER > +/* > + * kretprobe_trampoline skips updating frame pointer. The frame pointer > + * saved in trampoline_handler points to the real caller function's > + * frame pointer. > + */ > +STACK_FRAME_NON_STANDARD(kretprobe_trampoline); > +#endif > > /* > * Called from kretprobe_trampoline Ack.
On Sun, 21 Mar 2021 12:52:03 -0500 Josh Poimboeuf <jpoimboe@redhat.com> wrote: > On Sat, Mar 20, 2021 at 10:05:43PM +0900, Masami Hiramatsu wrote: > > On Sat, 20 Mar 2021 21:16:16 +0900 > > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > > > On Fri, 19 Mar 2021 21:22:39 +0900 > > > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > > > > > From: Josh Poimboeuf <jpoimboe@redhat.com> > > > > > > > > Add UNWIND_HINT_FUNC on kretporbe_trampoline code so that ORC > > > > information is generated on the kretprobe_trampoline correctly. > > > > > > > > > > Test bot also found a new warning for this. > > > > > > > >> arch/x86/kernel/kprobes/core.o: warning: objtool: kretprobe_trampoline()+0x25: call without frame pointer save/setup > > > > > > With CONFIG_FRAME_POINTER=y. > > > > > > Of course this can be fixed with additional "push %bp; mov %sp, %bp" before calling > > > trampoline_handler. But actually we know that this function has a bit special > > > stack frame too. > > > > > > Can I recover STACK_FRAME_NON_STANDARD(kretprobe_trampoline) when CONFIG_FRAME_POINTER=y ? > > > > So something like this. Does it work? > > > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > > index b31058a152b6..651f337dc880 100644 > > --- a/arch/x86/kernel/kprobes/core.c > > +++ b/arch/x86/kernel/kprobes/core.c > > @@ -760,6 +760,10 @@ int kprobe_int3_handler(struct pt_regs *regs) > > } > > NOKPROBE_SYMBOL(kprobe_int3_handler); > > > > +#ifdef CONFIG_FRAME_POINTER > > +#undef UNWIND_HINT_FUNC > > +#define UNWIND_HINT_FUNC > > +#endif > > This hunk isn't necessary. The unwind hints don't actually have an > effect with frame pointers. Without this, objtool shows the following warning with CONFIG_FRAME_POINTER=y. arch/x86/kernel/kprobes/core.o: warning: objtool: kretprobe_trampoline()+0x1: BUG: why am I validating an ignored function? It seems to complain about putting UNWIND_HINT on STACK_FRAME_NON_STANDARD function. > > > /* > > * When a retprobed function returns, this code saves registers and > > * calls trampoline_handler() runs, which calls the kretprobe's handler. > > @@ -797,7 +801,14 @@ asm( > > ".size kretprobe_trampoline, .-kretprobe_trampoline\n" > > ); > > NOKPROBE_SYMBOL(kretprobe_trampoline); > > - > > +#ifdef CONFIG_FRAME_POINTER > > +/* > > + * kretprobe_trampoline skips updating frame pointer. The frame pointer > > + * saved in trampoline_handler points to the real caller function's > > + * frame pointer. > > + */ > > +STACK_FRAME_NON_STANDARD(kretprobe_trampoline); > > +#endif > > > > /* > > * Called from kretprobe_trampoline > > Ack. Thank you! > > -- > Josh >
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 427d648fffcd..b31058a152b6 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -772,6 +772,7 @@ 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" @@ -782,6 +783,7 @@ asm( " popfq\n" #else " pushl %esp\n" + UNWIND_HINT_FUNC " pushfl\n" SAVE_REGS_STRING " movl %esp, %eax\n" @@ -795,7 +797,6 @@ asm( ".size kretprobe_trampoline, .-kretprobe_trampoline\n" ); NOKPROBE_SYMBOL(kretprobe_trampoline); -STACK_FRAME_NON_STANDARD(kretprobe_trampoline); /*