Commit e3944bfa authored Feb 10, 2009 by Steven Rostedt

tracing, x86: fix fixup section to return to original code



Impact: fix to prevent a kernel crash on fault

If for some reason the pointer to the parent function on the
stack takes a fault, the fix up code will not return back to
the original faulting code. This can lead to unpredictable
results and perhaps even a kernel panic.

A fault should not happen, but if it does, we should simply
disable the tracer, warn, and continue running the kernel.
It should not lead to a kernel crash.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

parent acd89579

arch/x86/kernel/ftrace.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -491,13 +491,15 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
		"1: " _ASM_MOV " (%[parent_old]), %[old]\n"
		"2: " _ASM_MOV " %[return_hooker], (%[parent_replaced])\n"
		" movl $0, %[faulted]\n"
		"3:\n"

		".section .fixup, \"ax\"\n"
		"3: movl $1, %[faulted]\n"
		"4: movl $1, %[faulted]\n"
		" jmp 3b\n"
		".previous\n"

		_ASM_EXTABLE(1b, 3b)
		_ASM_EXTABLE(2b, 3b)
		_ASM_EXTABLE(1b, 4b)
		_ASM_EXTABLE(2b, 4b)

		: [parent_replaced] "=r" (parent), [old] "=r" (old),
		[faulted] "=r" (faulted)

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