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Date: Tue, 21 Apr 2020 20:33:45 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: tglx@...utronix.de, jpoimboe@...hat.com,
linux-kernel@...r.kernel.org, x86@...nel.org, mhiramat@...nel.org,
mbenes@...e.cz, jthierry@...hat.com, alexandre.chartre@...cle.com
Subject: Re: [PATCH v5 04/17] x86,ftrace: Fix ftrace_regs_caller() unwind
Hi Peter,
After looking at the code, I realized that the only possible way to do
the "direct call" part, is if the direct function helper is executed
there. All other ftrace_ops, will not call that path.
I added a trampoline that points to ftrace_regs_caller to the direct
ftrace_ops, to force it never to allocate its own trampoline, and thus
no created trampoline should ever do the jump for a direct caller.
By doing this, I was able to move the code around to be a bit simpler,
and not need the double modifications (the double ret).
Of course, if any created trampoline were to touch the ORIG_RAX, then
it would crash. We could always nop that compare in the created
trampoline if that is a concern.
Anyway, I added the below patch on top of your patches and it appears
to work. Thoughts?
-- Steve
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 867c126ddabe..2e11250d5647 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -367,13 +367,6 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
if (WARN_ON(ret < 0))
goto fail;
- if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
- ip = trampoline + (ftrace_regs_caller_ret - ftrace_regs_caller);
- ret = probe_kernel_read(ip, (void *)retq, RET_SIZE);
- if (WARN_ON(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 9738ed23964e..1f2afaa8f71f 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -241,22 +241,9 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
*/
movq ORIG_RAX(%rsp), %rax
testq %rax, %rax
- jz 1f
+ jnz 1f
- /* Swap the flags with orig_rax */
- movq MCOUNT_REG_SIZE(%rsp), %rdi
- movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
- movq %rax, MCOUNT_REG_SIZE(%rsp)
-
- restore_mcount_regs 8
- /* Restore flags */
- popfq
-
-SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL);
- UNWIND_HINT_RET_OFFSET
- jmp ftrace_epilogue
-
-1: restore_mcount_regs
+ restore_mcount_regs
/* Restore flags */
popfq
@@ -267,8 +254,19 @@ SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL);
* to the return.
*/
SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
+ UNWIND_HINT_RET_OFFSET
jmp ftrace_epilogue
+ /* Swap the flags with orig_rax */
+1: movq MCOUNT_REG_SIZE(%rsp), %rdi
+ movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
+ movq %rax, MCOUNT_REG_SIZE(%rsp)
+
+ restore_mcount_regs 8
+ /* Restore flags */
+ popfq
+ jmp ftrace_epilogue
+
SYM_FUNC_END(ftrace_regs_caller)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 041694a1eb74..8f540eef7511 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2399,6 +2399,13 @@ struct ftrace_ops direct_ops = {
.flags = FTRACE_OPS_FL_IPMODIFY | FTRACE_OPS_FL_RECURSION_SAFE
| FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS
| FTRACE_OPS_FL_PERMANENT,
+ /*
+ * By declaring the main trampoline as this trampoline
+ * it will never have one allocated for it. This is fine
+ * as this should only be used if we are in the
+ * ftrace_ops_list function.
+ */
+ .trampoline = FTRACE_REGS_ADDR,
};
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
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