x86: mmiotrace - trace memory mapped IO

Mmiotrace is a tool for trapping memory mapped IO (MMIO) accesses within
the kernel. It is used for debugging and especially for reverse
engineering evil binary drivers.

Mmiotrace works by wrapping the ioremap family of kernel functions and
marking the returned pages as not present. Access to the IO memory
triggers a page fault, which will be handled by mmiotrace's custom page
fault handler. This will single-step the faulted instruction with the
MMIO page marked as present. Access logs are directed to user space via
relay and debug_fs.

This page fault approach is necessary, because binary drivers have
readl/writel etc. calls inlined and therefore extremely difficult to
trap with with e.g. kprobes.

This patch depends on the custom page fault handlers patch.

Signed-off-by: Pekka Paalanen <pq@iki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 27 insertions, 0 deletions

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 9431a8399844..7c6496e2225e 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -176,6 +176,33 @@ config PAGE_FAULT_HANDLERS
           register a function that is called on every page fault. Custom
           handlers are used by some debugging and reverse engineering tools.
 
+config MMIOTRACE
+        tristate "Memory mapped IO tracing"
+        depends on DEBUG_KERNEL && PAGE_FAULT_HANDLERS && RELAY && DEBUG_FS
+        default n
+        help
+          This will build a kernel module called mmiotrace.
+
+          Mmiotrace traces Memory Mapped I/O access and is meant for debugging
+          and reverse engineering. The kernel module offers wrapped
+          versions of the ioremap family of functions. The driver to be traced
+          must be modified to call these wrappers. A user space program is
+          required to collect the MMIO data.
+
+          See http://nouveau.freedesktop.org/wiki/MmioTrace
+          If you are not helping to develop drivers, say N.
+
+config MMIOTRACE_TEST
+        tristate "Test module for mmiotrace"
+        depends on MMIOTRACE && m
+        default n
+        help
+          This is a dumb module for testing mmiotrace. It is very dangerous
+          as it will write garbage to IO memory starting at a given address.
+          However, it should be safe to use on e.g. unused portion of VRAM.
+
+          Say N, unless you absolutely know what you are doing.
+
 #
 # IO delay types:
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