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Update zeroize test to use mbedtls_platform_zeroize()

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This commit is contained in:
Andres Amaya Garcia 2018-04-17 10:14:53 -05:00
parent 9644983ae4
commit eecea0e281
2 changed files with 22 additions and 21 deletions
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13
programs/test/zeroize.c
View file

@ -2,13 +2,14 @@
* Zeroize application for debugger-driven testing
*
* This is a simple test application used for debugger-driven testing to check
* whether calls to mbedtls_zeroize() are being eliminated by compiler
* whether calls to mbedtls_platform_zeroize() are being eliminated by compiler
* optimizations. This application is used by the GDB script at
* tests/scripts/test_zeroize.gdb under the assumption that line numbers do not
* tests/scripts/test_zeroize.gdb under the assumption that the code does not
* change often (as opposed to the library code) because the script sets a
* breakpoint at the last return statement in the main() function of this
* program. The debugger facilities are then used to manually inspect the
* memory and verify that the call to mbedtls_zeroize() was not eliminated.
* memory and verify that the call to mbedtls_platform_zeroize() was not
* eliminated.
*
* Copyright (C) 2018, Arm Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0
@ -45,14 +46,14 @@
#define MBEDTLS_EXIT_FAILURE EXIT_FAILURE
#endif
#include "mbedtls/utils.h"
#include "mbedtls/platform_util.h"
#define BUFFER_LEN 1024
void usage( void )
{
mbedtls_printf( "Zeroize is a simple program to assist with testing\n" );
mbedtls_printf( "the mbedtls_zeroize() function by using the\n" );
mbedtls_printf( "the mbedtls_platform_zeroize() function by using the\n" );
mbedtls_printf( "debugger. This program takes a file as input and\n" );
mbedtls_printf( "prints the first %d characters. Usage:\n\n", BUFFER_LEN );
mbedtls_printf( " zeroize <FILE>\n" );
@ -94,7 +95,7 @@ int main( int argc, char** argv )
mbedtls_printf( "The file is empty!\n" );
fclose( fp );
mbedtls_zeroize( buf, sizeof( buf ) );
mbedtls_platform_zeroize( buf, sizeof( buf ) );
return( exit_code );
}

30
tests/scripts/test_zeroize.gdb
View file

@ -6,29 +6,29 @@
#
# Purpose
#
# Run a test using the debugger to check that the mbedtls_zeroize() function in
# utils.h is not being optimized out by the compiler. To do so, the script
# loads the test program at programs/test/zeroize.c and sets a breakpoint at
# the last return statement in the main(). When the breakpoint is hit, the
# debugger manually checks the contents to be zeroized and checks that it is
# actually cleared.
# Run a test using the debugger to check that the mbedtls_platform_zeroize()
# function in platform_util.h is not being optimized out by the compiler. To do
# so, the script loads the test program at programs/test/zeroize.c and sets a
# breakpoint at the last return statement in main(). When the breakpoint is
# hit, the debugger manually checks the contents to be zeroized and checks that
# it is actually cleared.
#
# The mbedtls_zeroize() test is debugger driven because there does not seem to
# be a mechanism to reliably check whether the zeroize calls are being
# The mbedtls_platform_zeroize() test is debugger driven because there does not
# seem to be a mechanism to reliably check whether the zeroize calls are being
# eliminated by compiler optimizations from within the compiled program. The
# problem is that a compiler would typically remove what it considers to be
# "unecessary" assignments as part of redundant code elimination. To identify
# such code, the compilar will create some form dependency graph between
# reads and writes to variables (among other situations). It will then use this
# data structure to remove redundant code that does not have an impact on the
# program's observable behavior. In the case of mbedtls_zeroize(), an
# program's observable behavior. In the case of mbedtls_platform_zeroize(), an
# intelligent compiler could determine that this function clears a block of
# memory that is not accessed later in the program, so removing the call to
# mbedtls_zeroize() does not have an observable behavior. However, inserting a
# test after a call to mbedtls_zeroize() to check whether the block of
# memory was correctly zeroed would force the compiler to not eliminate the
# mbedtls_zeroize() call. If this does not occur, then the compiler potentially
# has a bug.
# mbedtls_platform_zeroize() does not have an observable behavior. However,
# inserting a test after a call to mbedtls_zeroize() to check whether the block
# of memory was correctly zeroed would force the compiler to not eliminate the
# mbedtls_platform_zeroize() call. If this does not occur, then the compiler
# potentially has a bug.
#
# Note: This test requires that the test program is compiled with -g3.
#
@ -42,7 +42,7 @@
set confirm off
file ./programs/test/zeroize
break zeroize.c:99
break zeroize.c:100
set args ./programs/test/zeroize.c
run