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x86/ftrace: Remove fault protection code in prepare_ftrace_return

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Removing the fault protection code when writing return_hooker
to stack. As Steven noted:

> That protection was there from the beginning due to being "paranoid",
> considering ftrace was bricking network cards. But that protection
> would not have even protected against that.

Link: https://lkml.kernel.org/r/20211008091336.33616-3-jolsa@kernel.org

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2021-10-08 11:13:30 +02:00
parent 1e85010e17
commit 8646698aef
1 changed files with 3 additions and 35 deletions
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38
arch/x86/kernel/ftrace.c
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@ -620,12 +620,10 @@ int ftrace_disable_ftrace_graph_caller(void)
* Hook the return address and push it in the stack of return addrs
* in current thread info.
*/
void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
void prepare_ftrace_return(unsigned long ip, unsigned long *parent,
unsigned long frame_pointer)
{
unsigned long return_hooker = (unsigned long)&return_to_handler;
unsigned long old;
int faulted;
/*
* When resuming from suspend-to-ram, this function can be indirectly
@ -645,37 +643,7 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
if (unlikely(atomic_read(&current->tracing_graph_pause)))
return;
/*
* Protect against fault, even if it shouldn't
* happen. This tool is too much intrusive to
* ignore such a protection.
*/
asm volatile(
"1: " _ASM_MOV " (%[parent]), %[old]\n"
"2: " _ASM_MOV " %[return_hooker], (%[parent])\n"
" movl $0, %[faulted]\n"
"3:\n"
".section .fixup, \"ax\"\n"
"4: movl $1, %[faulted]\n"
" jmp 3b\n"
".previous\n"
_ASM_EXTABLE(1b, 4b)
_ASM_EXTABLE(2b, 4b)
: [old] "=&r" (old), [faulted] "=r" (faulted)
: [parent] "r" (parent), [return_hooker] "r" (return_hooker)
: "memory"
);
if (unlikely(faulted)) {
ftrace_graph_stop();
WARN_ON(1);
return;
}
if (function_graph_enter(old, self_addr, frame_pointer, parent))
*parent = old;
if (!function_graph_enter(*parent, ip, frame_pointer, parent))
*parent = return_hooker;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */