224a95f124
Cherry-picked from libfido2 upstream f20a735c0a6f: iso7816: Avoid storing pointers in a packed structure On CHERI, and thus Arm's experimental Morello prototype architecture, pointers are represented as capabilities, which are unforgeable bounded pointers, providing always-on fine-grained spatial memory safety. The unforgeability is enforced through the use of tagged memory, with one validity tag bit per capability-sized-and-aligned word in memory. This means that storing a pointer to an unaligned location, which is not guaranteed to work per the C standard, either traps or results in the capability losing its tag (and thus never being dereferenceable again), depending on how exactly the store is done (specifically, whether a capability store or memcpy is used). However, iso7816 itself does not need to be packed, and doing so likely causes inefficiencies on existing architectures. The iso7816_header_t member is packed, and the flexible payload array is a uint8_t (which by definition has no padding bits and is exactly 8 bits in size and, since CHAR_BITS must be at least 8, its existence implies that it has the same representation as unsigned char, and that it has size and alignment 1) so there will never be any padding inserted between header and payload (but payload may overlap with padding at the end of the struct due to how flexible arrays work, which means we need to be careful about our calculations). Co-authored-by: pedro martelletto <pedro@yubico.com>
65 lines
1.5 KiB
C
65 lines
1.5 KiB
C
/*
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* Copyright (c) 2018 Yubico AB. All rights reserved.
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* Use of this source code is governed by a BSD-style
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* license that can be found in the LICENSE file.
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*/
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#include "fido.h"
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iso7816_apdu_t *
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iso7816_new(uint8_t cla, uint8_t ins, uint8_t p1, uint16_t payload_len)
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{
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iso7816_apdu_t *apdu;
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size_t alloc_len;
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alloc_len = sizeof(iso7816_apdu_t) + payload_len + 2; /* le1 le2 */
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if ((apdu = calloc(1, alloc_len)) == NULL)
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return NULL;
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apdu->alloc_len = alloc_len;
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apdu->payload_len = payload_len;
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apdu->payload_ptr = apdu->payload;
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apdu->header.cla = cla;
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apdu->header.ins = ins;
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apdu->header.p1 = p1;
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apdu->header.lc2 = (uint8_t)((payload_len >> 8) & 0xff);
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apdu->header.lc3 = (uint8_t)(payload_len & 0xff);
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return apdu;
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}
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void
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iso7816_free(iso7816_apdu_t **apdu_p)
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{
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iso7816_apdu_t *apdu;
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if (apdu_p == NULL || (apdu = *apdu_p) == NULL)
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return;
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freezero(apdu, apdu->alloc_len);
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*apdu_p = NULL;
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}
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int
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iso7816_add(iso7816_apdu_t *apdu, const void *buf, size_t cnt)
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{
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if (cnt > apdu->payload_len || cnt > UINT16_MAX)
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return -1;
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memcpy(apdu->payload_ptr, buf, cnt);
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apdu->payload_ptr += cnt;
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apdu->payload_len = (uint16_t)(apdu->payload_len - cnt);
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return 0;
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}
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const unsigned char *
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iso7816_ptr(const iso7816_apdu_t *apdu)
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{
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return (const unsigned char *)&apdu->header;
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}
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size_t
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iso7816_len(const iso7816_apdu_t *apdu)
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{
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return apdu->alloc_len - offsetof(iso7816_apdu_t, header) -
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(sizeof(iso7816_apdu_t) - offsetof(iso7816_apdu_t, payload));
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}
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