Messages in this thread | | | Date | Wed, 22 Apr 2020 22:08:08 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 3/3] x86/ftrace: Do not jump to direct code in created trampolines |
| |
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[] ?
> + 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.
| |