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linux/kernel/trace/trace_export.c
Steven Rostedt (Google) e7186af7fb tracing: Add back FORTIFY_SOURCE logic to kernel_stack event structure 
For backward compatibility, older tooling expects to see the kernel_stack
event with a "caller" field that is a fixed size array of 8 addresses. The
code now supports more than 8 with an added "size" field that states the
real number of entries. But the "caller" field still just looks like a
fixed size to user space.

Since the tracing macros that create the user space format files also
creates the structures that those files represent, the kernel_stack event
structure had its "caller" field a fixed size of 8, but in reality, when
it is allocated on the ring buffer, it can hold more if the stack trace is
bigger that 8 functions. The copying of these entries was simply done with
a memcpy():

  size = nr_entries * sizeof(unsigned long);
  memcpy(entry->caller, fstack->calls, size);

The FORTIFY_SOURCE logic noticed at runtime that when the nr_entries was
larger than 8, that the memcpy() was writing more than what the structure
stated it can hold and it complained about it. This is because the
FORTIFY_SOURCE code is unaware that the amount allocated is actually
enough to hold the size. It does not expect that a fixed size field will
hold more than the fixed size.

This was originally solved by hiding the caller assignment with some
pointer arithmetic.

  ptr = ring_buffer_data();
  entry = ptr;

  ptr += offsetof(typeof(*entry), caller);
  memcpy(ptr, fstack->calls, size);

But it is considered bad form to hide from kernel hardening. Instead, make
it work nicely with FORTIFY_SOURCE by adding a new __stack_array() macro
that is specific for this one special use case. The macro will take 4
arguments: type, item, len, field (whereas the __array() macro takes just
the first three). This macro will act just like the __array() macro when
creating the code to deal with the format file that is exposed to user
space. But for the kernel, it will turn the caller field into:

  type item[] __counted_by(field);

or for this instance:

  unsigned long caller[] __counted_by(size);

Now the kernel code can expose the assignment of the caller to the
FORTIFY_SOURCE and everyone is happy!

Link: https://lore.kernel.org/linux-trace-kernel/20230712105235.5fc441aa@gandalf.local.home/
Link: https://lore.kernel.org/linux-trace-kernel/20230713092605.2ddb9788@rorschach.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
2023-07-30 18:11:44 -04:00

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// SPDX-License-Identifier: GPL-2.0
/*
* trace_export.c - export basic ftrace utilities to user space
*
* Copyright (C) 2009 Steven Rostedt <srostedt@redhat.com>
*/
#include <linux/stringify.h>
#include <linux/kallsyms.h>
#include <linux/seq_file.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/init.h>
#include "trace_output.h"
/* Stub function for events with triggers */
static int ftrace_event_register(struct trace_event_call *call,
enum trace_reg type, void *data)
{
return 0;
}
#undef TRACE_SYSTEM
#define TRACE_SYSTEM ftrace
/*
* The FTRACE_ENTRY_REG macro allows ftrace entry to define register
* function and thus become accessible via perf.
*/
#undef FTRACE_ENTRY_REG
#define FTRACE_ENTRY_REG(name, struct_name, id, tstruct, print, regfn) \
FTRACE_ENTRY(name, struct_name, id, PARAMS(tstruct), PARAMS(print))
/* not needed for this file */
#undef __field_struct
#define __field_struct(type, item)
#undef __field
#define __field(type, item) type item;
#undef __field_fn
#define __field_fn(type, item) type item;
#undef __field_desc
#define __field_desc(type, container, item) type item;
#undef __field_packed
#define __field_packed(type, container, item) type item;
#undef __array
#define __array(type, item, size) type item[size];
#undef __stack_array
#define __stack_array(type, item, size, field) __array(type, item, size)
#undef __array_desc
#define __array_desc(type, container, item, size) type item[size];
#undef __dynamic_array
#define __dynamic_array(type, item) type item[];
#undef F_STRUCT
#define F_STRUCT(args...) args
#undef F_printk
#define F_printk(fmt, args...) fmt, args
#undef FTRACE_ENTRY
#define FTRACE_ENTRY(name, struct_name, id, tstruct, print) \
struct ____ftrace_##name { \
tstruct \
}; \
static void __always_unused ____ftrace_check_##name(void) \
{ \
struct ____ftrace_##name *__entry = NULL; \
\
/* force compile-time check on F_printk() */ \
printk(print); \
}
#undef FTRACE_ENTRY_DUP
#define FTRACE_ENTRY_DUP(name, struct_name, id, tstruct, print) \
FTRACE_ENTRY(name, struct_name, id, PARAMS(tstruct), PARAMS(print))
#include "trace_entries.h"
#undef __field_ext
#define __field_ext(_type, _item, _filter_type) { \
.type = #_type, .name = #_item, \
.size = sizeof(_type), .align = __alignof__(_type), \
is_signed_type(_type), .filter_type = _filter_type },
#undef __field_ext_packed
#define __field_ext_packed(_type, _item, _filter_type) { \
.type = #_type, .name = #_item, \
.size = sizeof(_type), .align = 1, \
is_signed_type(_type), .filter_type = _filter_type },
#undef __field
#define __field(_type, _item) __field_ext(_type, _item, FILTER_OTHER)
#undef __field_fn
#define __field_fn(_type, _item) __field_ext(_type, _item, FILTER_TRACE_FN)
#undef __field_desc
#define __field_desc(_type, _container, _item) __field_ext(_type, _item, FILTER_OTHER)
#undef __field_packed
#define __field_packed(_type, _container, _item) __field_ext_packed(_type, _item, FILTER_OTHER)
#undef __array
#define __array(_type, _item, _len) { \
.type = #_type"["__stringify(_len)"]", .name = #_item, \
.size = sizeof(_type[_len]), .align = __alignof__(_type), \
is_signed_type(_type), .filter_type = FILTER_OTHER, \
.len = _len },
#undef __stack_array
#define __stack_array(_type, _item, _len, _field) __array(_type, _item, _len)
#undef __array_desc
#define __array_desc(_type, _container, _item, _len) __array(_type, _item, _len)
#undef __dynamic_array
#define __dynamic_array(_type, _item) { \
.type = #_type "[]", .name = #_item, \
.size = 0, .align = __alignof__(_type), \
is_signed_type(_type), .filter_type = FILTER_OTHER },
#undef FTRACE_ENTRY
#define FTRACE_ENTRY(name, struct_name, id, tstruct, print) \
static struct trace_event_fields ftrace_event_fields_##name[] = { \
tstruct \
{} };
#include "trace_entries.h"
#undef __entry
#define __entry REC
#undef __field
#define __field(type, item)
#undef __field_fn
#define __field_fn(type, item)
#undef __field_desc
#define __field_desc(type, container, item)
#undef __field_packed
#define __field_packed(type, container, item)
#undef __array
#define __array(type, item, len)
#undef __stack_array
#define __stack_array(type, item, len, field)
#undef __array_desc
#define __array_desc(type, container, item, len)
#undef __dynamic_array
#define __dynamic_array(type, item)
#undef F_printk
#define F_printk(fmt, args...) __stringify(fmt) ", " __stringify(args)
#undef FTRACE_ENTRY_REG
#define FTRACE_ENTRY_REG(call, struct_name, etype, tstruct, print, regfn) \
static struct trace_event_class __refdata event_class_ftrace_##call = { \
.system = __stringify(TRACE_SYSTEM), \
.fields_array = ftrace_event_fields_##call, \
.fields = LIST_HEAD_INIT(event_class_ftrace_##call.fields),\
.reg = regfn, \
}; \
\
struct trace_event_call __used event_##call = { \
.class = &event_class_ftrace_##call, \
{ \
.name = #call, \
}, \
.event.type = etype, \
.print_fmt = print, \
.flags = TRACE_EVENT_FL_IGNORE_ENABLE, \
}; \
static struct trace_event_call __used \
__section("_ftrace_events") *__event_##call = &event_##call;
#undef FTRACE_ENTRY
#define FTRACE_ENTRY(call, struct_name, etype, tstruct, print) \
FTRACE_ENTRY_REG(call, struct_name, etype, \
PARAMS(tstruct), PARAMS(print), NULL)
bool ftrace_event_is_function(struct trace_event_call *call)
{
return call == &event_function;
}
#include "trace_entries.h"
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