Messages in this thread | | | Date | Wed, 22 Apr 2020 16:17:25 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH 3/3] x86/ftrace: Do not jump to direct code in created trampolines |
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On Wed, 22 Apr 2020 22:08:08 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Apr 22, 2020 at 12:25:42PM -0400, Steven Rostedt wrote: > > > @@ -367,6 +371,17 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) > > if (WARN_ON(ret < 0)) > > goto fail; > > > > + /* No need to test direct calls on created trampolines */ > > + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { > > + /* NOP the jnz 1f; but make sure it's a 2 byte jnz */ > > + ip = trampoline + (jmp_offset - start_offset); > > + if (WARN_ON(*(char *)ip != 0x75)) > > + goto fail; > > + ret = probe_kernel_read(ip, ideal_nops[2], 2); > > Now you're just being silly, are you really, actually worried you can't > read ideal_nops[] ?
Hah, that was more cut and paste. I guess a memcpy() would be more appropriate.
> > > + if (ret < 0) > > + goto fail; > > + } > > + > > /* > > * The address of the ftrace_ops that is used for this trampoline > > * is stored at the end of the trampoline. This will be used to > > diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S > > index 0882758d165a..f72ef157feb3 100644 > > --- a/arch/x86/kernel/ftrace_64.S > > +++ b/arch/x86/kernel/ftrace_64.S > > @@ -241,6 +241,7 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL) > > */ > > movq ORIG_RAX(%rsp), %rax > > testq %rax, %rax > > +SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL) > > jnz 1f > > > > I you worry about performance, it would make more sense to do something > like so: > > SYM_INNER_LABEL(ftrace_regs_caller_from, SYM_L_GLOBAL) > movq ORIG_RAX(%rsp), %rax > testq %rax, %rax > jnz 1f > SYM_INNER_LABEL(ftrace_regs_caller_to, SYM_L_GLOBAL) > > if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { > ip = trampoline + (ftrace_regs_caller_from - start_offset); > ((u8[])ip)[0] = JMP8_INSN_OPCODE; > ((u8[])ip)[1] = ftrace_regs_caller_to - ftrace_regs_caller_from - JMP8_INSN_SIZE; > } > > Or nop the whole range, but it's like 10 bytes so I'm not sure that's > actually faster.
That could work too. I'll play with that and actually do some benchmarks to see how much it affects things.
Thanks!
-- Steve
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