git: 224a95f12427 - main - libfido2: Address CHERI compatibility

The branch main has been updated by emaste:

URL: https://cgit.FreeBSD.org/src/commit/?id=224a95f124270275ddd7ab9f8f87dd47bad7c282

commit 224a95f124270275ddd7ab9f8f87dd47bad7c282
Author:     Jessica Clarke <jrtc27@jrtc27.com>
AuthorDate: 2021-10-02 15:51:38 +0000
Commit:     Ed Maste <emaste@FreeBSD.org>
CommitDate: 2021-10-07 01:40:26 +0000

    libfido2: Address CHERI compatibility
    
    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>
---
 contrib/libfido2/src/iso7816.c | 4 ++--
 contrib/libfido2/src/iso7816.h | 5 ++---
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/contrib/libfido2/src/iso7816.c b/contrib/libfido2/src/iso7816.c
index a11aae3e99d1..a4902277c6d8 100644
--- a/contrib/libfido2/src/iso7816.c
+++ b/contrib/libfido2/src/iso7816.c
@@ -59,6 +59,6 @@ iso7816_ptr(const iso7816_apdu_t *apdu)
 size_t
 iso7816_len(const iso7816_apdu_t *apdu)
 {
-	return apdu->alloc_len - sizeof(apdu->alloc_len) -
-	    sizeof(apdu->payload_len) - sizeof(apdu->payload_ptr);
+	return apdu->alloc_len - offsetof(iso7816_apdu_t, header) -
+	    (sizeof(iso7816_apdu_t) - offsetof(iso7816_apdu_t, payload));
 }
diff --git a/contrib/libfido2/src/iso7816.h b/contrib/libfido2/src/iso7816.h
index 5f5363a63a56..9bfad1fbab9d 100644
--- a/contrib/libfido2/src/iso7816.h
+++ b/contrib/libfido2/src/iso7816.h
@@ -27,14 +27,13 @@ struct iso7816_header {
 	uint8_t lc3;
 })
 
-PACKED_TYPE(iso7816_apdu_t,
-struct iso7816_apdu {
+typedef struct iso7816_apdu {
 	size_t            alloc_len;
 	uint16_t          payload_len;
 	uint8_t          *payload_ptr;
 	iso7816_header_t  header;
 	uint8_t           payload[];
-})
+} iso7816_apdu_t;
 
 const unsigned char *iso7816_ptr(const iso7816_apdu_t *);
 int iso7816_add(iso7816_apdu_t *, const void *, size_t);