old-cross-binutils/gdb/testsuite/gdb.base/breakpoint-in-ro-region.exp
Pedro Alves 0fec99e8be Really fail inserting software breakpoints on read-only regions
Currently, with "set breakpoint auto-hw off", we'll still try to
insert a software breakpoint at addresses covered by supposedly
read-only or inacessible regions:

 (top-gdb) mem 0x443000 0x450000 ro
 (top-gdb) set mem inaccessible-by-default off
 (top-gdb) disassemble
 Dump of assembler code for function main:
    0x0000000000443956 <+34>:    movq   $0x0,0x10(%rax)
 => 0x000000000044395e <+42>:    movq   $0x0,0x18(%rax)
    0x0000000000443966 <+50>:    mov    -0x24(%rbp),%eax
    0x0000000000443969 <+53>:    mov    %eax,-0x20(%rbp)
 End of assembler dump.
 (top-gdb) b *0x0000000000443969
 Breakpoint 5 at 0x443969: file ../../src/gdb/gdb.c, line 29.
 (top-gdb) c
 Continuing.
 warning: cannot set software breakpoint at readonly address 0x443969

 Breakpoint 5, 0x0000000000443969 in main (argc=1, argv=0x7fffffffd918) at ../../src/gdb/gdb.c:29
 29        args.argc = argc;
 (top-gdb)

We warn, saying that the insertion can't be done, but then proceed
attempting the insertion anyway, and in case of manually added
regions, the insert actually succeeds.

This is a regression; GDB used to fail inserting the breakpoint.  More
below.

I stumbled on this as I wrote a test that manually sets up a read-only
memory region with the "mem" command, in order to test GDB's behavior
with breakpoints set on read-only regions, even when the real memory
the breakpoints are set at isn't really read-only.  I wanted that in
order to add a test that exercises software single-stepping through
read-only regions.

Note that the memory regions that target_memory_map returns aren't
like e.g., what would expect to see in /proc/PID/maps on Linux.
Instead, they're the physical memory map from the _debuggers_
perspective.  E.g., a read-only region would be real ROM or flash
memory, while a read-only+execute mapping in /proc/PID/maps is still
read-write to the debugger (otherwise the debugger wouldn't be able to
set software breakpoints in the code segment).

If one tries to manually write to memory that falls within a memory
region that is known to be read-only, with e.g., "p foo = 1", then we
hit a check in memory_xfer_partial_1 before the write mananges to make
it to the target side.

But writing a software/memory breakpoint nowadays goes through
target_write_raw_memory, and unlike when writing memory with
TARGET_OBJECT_MEMORY, nothing on the TARGET_OBJECT_RAW_MEMORY path
checks whether we're trying to write to a read-only region.

At the time "breakpoint auto-hw" was added, we didn't have the
TARGET_OBJECT_MEMORY vs TARGET_OBJECT_RAW_MEMORY target object
distinction yet, and the code path in memory_xfer_partial that blocks
writes to read-only memory was hit for memory breakpoints too.  With
GDB 6.8 we had:

 warning: cannot set software breakpoint at readonly address 0000000000443943
 Warning:
 Cannot insert breakpoint 1.
 Error accessing memory address 0x443943: Input/output error.

So I started out by fixing this by adding the memory region validation
to TARGET_OBJECT_RAW_MEMORY too.

But later, when testing against GDBserver, I realized that that would
only block software/memory breakpoints GDB itself inserts with
gdb/mem-break.c.  If a target has a to_insert_breakpoint method, the
insertion request will still pass through to the target.  So I ended
up converting the "cannot set breakpoint" warning in breakpoint.c to a
real error return, thus blocking the insertion sooner.

With that, we'll end up no longer needing the TARGET_OBJECT_RAW_MEMORY
changes once software single-step breakpoints are converted to real
breakpoints.  We need them today as software single-step breakpoints
bypass insert_bp_location.  But, it'll be best to leave that in as
safeguard anyway, for other direct uses of TARGET_OBJECT_RAW_MEMORY.

Tested on x86_64 Fedora 20, native and gdbserver.

gdb/
2014-10-01  Pedro Alves  <palves@redhat.com>

	* breakpoint.c (insert_bp_location): Error out if inserting a
	software breakpoint at a read-only address.
	* target.c (memory_xfer_check_region): New function, factored out
	from ...
	(memory_xfer_partial_1): ... this.  Make the 'reg_len' local a
	ULONGEST.
	(target_xfer_partial) <TARGET_OBJECT_RAW_MEMORY>: Check the access
	against the memory region attributes.

gdb/testsuite/
2014-10-01  Pedro Alves  <palves@redhat.com>

	* gdb.base/breakpoint-in-ro-region.c: New file.
	* gdb.base/breakpoint-in-ro-region.exp: New file.
2014-10-01 23:31:55 +01:00

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# Copyright 2014 Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
# This file is part of the gdb testsuite
standard_testfile
if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
return -1
}
if ![runto main] {
return -1
}
delete_breakpoints
# Get the bounds of a function, and write them to FUNC_LO (inclusive),
# FUNC_HI (exclusive). Return true on success and false on failure.
proc get_function_bounds {function func_lo func_hi} {
global gdb_prompt
global hex decimal
upvar $func_lo lo
upvar $func_hi hi
set lo ""
set size ""
set test "get lo address of $function"
gdb_test_multiple "disassemble $function" $test {
-re "($hex) .*$hex <\\+($decimal)>:\[^\r\n\]+\r\nEnd of assembler dump\.\r\n$gdb_prompt $" {
set lo $expect_out(1,string)
set size $expect_out(2,string)
pass $test
}
}
if { $lo == "" || $size == "" } {
return false
}
# Account for the size of the last instruction.
set test "get hi address of $function"
gdb_test_multiple "x/2i $function+$size" $test {
-re ".*$hex <$function\\+$size>:\[^\r\n\]+\r\n\[ \]+($hex).*\.\r\n$gdb_prompt $" {
set hi $expect_out(1,string)
pass $test
}
}
if { $hi == "" } {
return false
}
# Remove unnecessary leading 0's (0x00000ADDR => 0xADDR) so we can
# easily do matches. Disassemble includes leading zeros, while
# x/i doesn't.
regsub -all "0x0\+" $lo "0x" lo
regsub -all "0x0\+" $hi "0x" hi
return true
}
# Get the address where the thread is currently stopped.
proc get_curr_insn {} {
global gdb_prompt
global hex
set pc ""
set test "get current insn"
gdb_test_multiple "p /x \$pc" $test {
-re " = ($hex)\r\n$gdb_prompt $" {
set pc $expect_out(1,string)
pass $test
}
}
return $pc
}
# Get the address of where a single-step should land.
proc get_next_insn {} {
global gdb_prompt
global hex
set next ""
set test "get next insn"
gdb_test_multiple "x/2i \$pc" $test {
-re "$hex .*:\[^\r\n\]+\r\n\[ \]+($hex).*\.\r\n$gdb_prompt $" {
set next $expect_out(1,string)
pass $test
}
}
return $next
}
if ![get_function_bounds "main" main_lo main_hi] {
# Can't do the following tests if main's bounds are unknown.
return -1
}
# Manually create a read-only memory region that covers 'main'.
gdb_test_no_output "mem $main_lo $main_hi ro" \
"create read-only mem region covering main"
# So that we don't fail inserting breakpoints on addresses outside
# main, like the internal event breakpoints.
gdb_test_no_output "set mem inaccessible-by-default off"
# So we get an immediate warning/error without needing to resume the
# target.
gdb_test_no_output "set breakpoint always-inserted on"
# Disable the automatic fallback to HW breakpoints. We want a
# software breakpoint to be attempted, and to fail.
gdb_test_no_output "set breakpoint auto-hw off"
# Confirm manual writes to the read-only memory region fail.
gdb_test "p /x *(char *) $main_lo = 1" \
"Cannot access memory at address $main_lo" \
"writing to read-only memory fails"
# Ensure that inserting a software breakpoint in a known-read-only
# region fails.
gdb_test "break *$main_lo" \
"Cannot insert breakpoint .*Cannot set software breakpoint at read-only address $main_lo.*" \
"inserting software breakpoint in read-only memory fails"