Secure memory fixes

[thirdparty/openssl.git] / doc / crypto / OPENSSL_secure_malloc.pod

=pod

=head1 NAME

CRYPTO_secure_malloc_init, CRYPTO_secure_malloc_initialized,
CRYPTO_secure_malloc_done, OPENSSL_secure_malloc, CRYPTO_secure_malloc,
OPENSSL_secure_zalloc, CRYPTO_secure_zalloc, OPENSSL_secure_free,
CRYPTO_secure_free, OPENSSL_secure_actual_size, OPENSSL_secure_allocated,
CYRPTO_secure_malloc_used - secure heap storage

=head1 SYNOPSIS

 #include <openssl/crypto.h>

 int CRYPTO_secure_malloc_init(size_t size, int minsize);

 int CRYPTO_secure_malloc_initialized();

 int CRYPTO_secure_malloc_done();

 void *OPENSSL_secure_malloc(size_t num);
 void *CRYPTO_secure_malloc(size_t num, const char *file, int line);

 void *OPENSSL_secure_zalloc(size_t num);
 void *CRYPTO_secure_zalloc(size_t num, const char *file, int line);

 void OPENSSL_secure_free(void* ptr);
 void CRYPTO_secure_free(void *ptr, const char *, int);

 size_t OPENSSL_secure_actual_size(const void *ptr);
 int OPENSSL_secure_allocated(const void *ptr);

 size_t CYRPTO_secure_used();

=head1 DESCRIPTION

In order to help protect applications (particularly long-running servers)
from pointer overruns or underruns that could return arbitrary data from
the program's dynamic memory area, where keys and other sensitive
information might be stored, OpenSSL supports the concept of a "secure heap."
The level and type of security guarantees depend on the operating system.
It is a good idea to review the code and see if it addresses your
threat model and concerns.

If a secure heap is used, then private key B<BIGNUM> values are stored there.
This protects long-term storage of private keys, but will not necessarily
put all intermediate values and computations there.

CRYPTO_secure_malloc_init() creates the secure heap, with the specified
C<size> in bytes. The C<minsize> parameter is the minimum size to
allocate from the heap. Both C<size> and C<minsize> must be a power
of two.

CRYPTO_secure_malloc_initialized() indicates whether or not the secure
heap as been initialized and is available.

CRYPTO_secure_malloc_done() releases the heap and makes the memory unavailable
to the process if all secure memory has been freed.
It can take noticeably long to complete. 

OPENSSL_secure_malloc() allocates C<num> bytes from the heap.
If CRYPTO_secure_malloc_init() is not called, this is equivalent to
calling OPENSSL_malloc().
It is a macro that expands to
CRYPTO_secure_malloc() and adds the C<__FILE__> and C<__LINE__> parameters.

OPENSSL_secure_zalloc() and CRYPTO_secure_zalloc() are like
OPENSSL_secure_malloc() and CRYPTO_secure_malloc(), respectively,
except that they call memset() to zero the memory before returning.

OPENSSL_secure_free() releases the memory at C<ptr> back to the heap.
It must be called with a value previously obtained from
OPENSSL_secure_malloc().
If CRYPTO_secure_malloc_init() is not called, this is equivalent to
calling OPENSSL_free().
It exists for consistency with OPENSSL_secure_malloc() , and
is a macro that expands to CRYPTO_secure_free() and adds the C<__FILE__>
and C<__LINE__> parameters..

OPENSSL_secure_allocated() tells whether or not a pointer is within
the secure heap.
OPENSSL_secure_actual_size() tells the actual size allocated to the
pointer; implementations may allocate more space than initially
requested, in order to "round up" and reduce secure heap fragmentation.

CRYPTO_secure_used() returns the number of bytes allocated in the
secure heap.

=head1 RETURN VALUES

CRYPTO_secure_malloc_init() returns 0 on failure, 1 if successful,
and 2 if successful but the heap could not be protected by memory
mapping.

CRYPTO_secure_malloc_initialized() returns 1 if the secure heap is
available (that is, if CRYPTO_secure_malloc_init() has been called,
but CRYPTO_secure_malloc_done() has not been called or failed) or 0 if not.

OPENSSL_secure_malloc() and OPENSSL_secure_zalloc() return a pointer into
the secure heap of the requested size, or C<NULL> if memory could not be
allocated.

CRYPTO_secure_allocated() returns 1 if the pointer is in the secure heap, or 0 if not.

CRYPTO_secure_malloc_done() returns 1 if the secure memory area is released, or 0 if not.

OPENSSL_secure_free() returns no values.

=head1 SEE ALSO

L<OPENSSL_malloc(3)>,
L<BN_new(3)>,
L<bn_internal(3)>.

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