Update zeroize test to use mbedtls_platform_zeroize()
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2 changed files with 22 additions and 21 deletions
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@ -2,13 +2,14 @@
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* Zeroize application for debugger-driven testing
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* Zeroize application for debugger-driven testing
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*
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*
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* This is a simple test application used for debugger-driven testing to check
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* This is a simple test application used for debugger-driven testing to check
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* whether calls to mbedtls_zeroize() are being eliminated by compiler
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* whether calls to mbedtls_platform_zeroize() are being eliminated by compiler
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* optimizations. This application is used by the GDB script at
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* optimizations. This application is used by the GDB script at
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* tests/scripts/test_zeroize.gdb under the assumption that line numbers do not
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* tests/scripts/test_zeroize.gdb under the assumption that the code does not
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* change often (as opposed to the library code) because the script sets a
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* change often (as opposed to the library code) because the script sets a
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* breakpoint at the last return statement in the main() function of this
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* breakpoint at the last return statement in the main() function of this
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* program. The debugger facilities are then used to manually inspect the
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* program. The debugger facilities are then used to manually inspect the
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* memory and verify that the call to mbedtls_zeroize() was not eliminated.
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* memory and verify that the call to mbedtls_platform_zeroize() was not
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* eliminated.
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*
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*
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* Copyright (C) 2018, Arm Limited, All Rights Reserved
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* Copyright (C) 2018, Arm Limited, All Rights Reserved
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* SPDX-License-Identifier: Apache-2.0
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* SPDX-License-Identifier: Apache-2.0
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@ -45,14 +46,14 @@
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#define MBEDTLS_EXIT_FAILURE EXIT_FAILURE
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#define MBEDTLS_EXIT_FAILURE EXIT_FAILURE
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#endif
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#endif
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#include "mbedtls/utils.h"
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#include "mbedtls/platform_util.h"
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#define BUFFER_LEN 1024
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#define BUFFER_LEN 1024
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void usage( void )
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void usage( void )
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{
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{
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mbedtls_printf( "Zeroize is a simple program to assist with testing\n" );
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mbedtls_printf( "Zeroize is a simple program to assist with testing\n" );
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mbedtls_printf( "the mbedtls_zeroize() function by using the\n" );
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mbedtls_printf( "the mbedtls_platform_zeroize() function by using the\n" );
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mbedtls_printf( "debugger. This program takes a file as input and\n" );
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mbedtls_printf( "debugger. This program takes a file as input and\n" );
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mbedtls_printf( "prints the first %d characters. Usage:\n\n", BUFFER_LEN );
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mbedtls_printf( "prints the first %d characters. Usage:\n\n", BUFFER_LEN );
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mbedtls_printf( " zeroize <FILE>\n" );
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mbedtls_printf( " zeroize <FILE>\n" );
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@ -94,7 +95,7 @@ int main( int argc, char** argv )
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mbedtls_printf( "The file is empty!\n" );
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mbedtls_printf( "The file is empty!\n" );
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fclose( fp );
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fclose( fp );
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mbedtls_zeroize( buf, sizeof( buf ) );
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mbedtls_platform_zeroize( buf, sizeof( buf ) );
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return( exit_code );
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return( exit_code );
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}
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}
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@ -6,29 +6,29 @@
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#
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#
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# Purpose
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# Purpose
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#
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#
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# Run a test using the debugger to check that the mbedtls_zeroize() function in
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# Run a test using the debugger to check that the mbedtls_platform_zeroize()
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# utils.h is not being optimized out by the compiler. To do so, the script
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# function in platform_util.h is not being optimized out by the compiler. To do
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# loads the test program at programs/test/zeroize.c and sets a breakpoint at
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# so, the script loads the test program at programs/test/zeroize.c and sets a
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# the last return statement in the main(). When the breakpoint is hit, the
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# breakpoint at the last return statement in main(). When the breakpoint is
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# debugger manually checks the contents to be zeroized and checks that it is
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# hit, the debugger manually checks the contents to be zeroized and checks that
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# actually cleared.
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# it is actually cleared.
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#
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#
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# The mbedtls_zeroize() test is debugger driven because there does not seem to
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# The mbedtls_platform_zeroize() test is debugger driven because there does not
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# be a mechanism to reliably check whether the zeroize calls are being
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# seem to be a mechanism to reliably check whether the zeroize calls are being
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# eliminated by compiler optimizations from within the compiled program. The
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# eliminated by compiler optimizations from within the compiled program. The
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# problem is that a compiler would typically remove what it considers to be
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# problem is that a compiler would typically remove what it considers to be
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# "unecessary" assignments as part of redundant code elimination. To identify
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# "unecessary" assignments as part of redundant code elimination. To identify
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# such code, the compilar will create some form dependency graph between
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# such code, the compilar will create some form dependency graph between
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# reads and writes to variables (among other situations). It will then use this
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# reads and writes to variables (among other situations). It will then use this
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# data structure to remove redundant code that does not have an impact on the
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# data structure to remove redundant code that does not have an impact on the
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# program's observable behavior. In the case of mbedtls_zeroize(), an
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# program's observable behavior. In the case of mbedtls_platform_zeroize(), an
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# intelligent compiler could determine that this function clears a block of
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# intelligent compiler could determine that this function clears a block of
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# memory that is not accessed later in the program, so removing the call to
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# memory that is not accessed later in the program, so removing the call to
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# mbedtls_zeroize() does not have an observable behavior. However, inserting a
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# mbedtls_platform_zeroize() does not have an observable behavior. However,
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# test after a call to mbedtls_zeroize() to check whether the block of
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# inserting a test after a call to mbedtls_zeroize() to check whether the block
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# memory was correctly zeroed would force the compiler to not eliminate the
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# of memory was correctly zeroed would force the compiler to not eliminate the
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# mbedtls_zeroize() call. If this does not occur, then the compiler potentially
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# mbedtls_platform_zeroize() call. If this does not occur, then the compiler
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# has a bug.
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# potentially has a bug.
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#
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#
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# Note: This test requires that the test program is compiled with -g3.
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# Note: This test requires that the test program is compiled with -g3.
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#
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#
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@ -42,7 +42,7 @@
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set confirm off
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set confirm off
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file ./programs/test/zeroize
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file ./programs/test/zeroize
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break zeroize.c:99
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break zeroize.c:100
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set args ./programs/test/zeroize.c
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set args ./programs/test/zeroize.c
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run
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run
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