From: H. Peter Anvin <hpa@linux.intel.com>
Date: Sat, 31 Aug 2013 00:29:29 +0000 (-0700)
Subject: x86-32, ftrace: Fix static ftrace when early microcode is enabled
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=af058ab04d3d11383e5159132fc78a3700be3af5;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git

x86-32, ftrace: Fix static ftrace when early microcode is enabled

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.kiszka@siemens.com>
Tested-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 2cfbc3a3a2dd..f0dcb0ceb6a2 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