Messages in this thread Patch in this message | | | Date | Tue, 21 Apr 2020 20:33:45 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v5 04/17] x86,ftrace: Fix ftrace_regs_caller() unwind |
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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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