From: "H. Peter Anvin" <h...@linux.intel.com>
Early microcode loading runs C code before paging is enabled on 32
bits. Since ftrace puts a hook into every function, that hook needs
to be safe to execute in the pre-paging environment. This is
currently true for dynamic ftrace but not for static ftrace.
Static ftrace is obsolescent and assumed to not be
performance-critical, so we can simply test that the stack pointer
falls within the valid range of kernel addresses.
Reported-by: Jan Kiszka <jan.kis...@siemens.com>
Tested-by: Jan Kiszka <jan.kis...@siemens.com>
Signed-off-by: H. Peter Anvin <h...@linux.intel.com>
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
---
arch/x86/kernel/entry_32.S | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 2cfbc3a..f0dcb0c 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1176,6 +1176,9 @@ ftrace_restore_flags:
#else /* ! CONFIG_DYNAMIC_FTRACE */
ENTRY(mcount)
+ cmpl $__PAGE_OFFSET, %esp
+ jb ftrace_stub /* Paging not enabled yet? */
+
cmpl $0, function_trace_stop
jne ftrace_stub
--
1.7.10.4
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