[RFC PATCH] efi_loader: add sha384/512 on certificate revocation
AKASHI Takahiro
takahiro.akashi at linaro.org
Mon Apr 11 10:31:08 CEST 2022
On Mon, Apr 11, 2022 at 10:56:22AM +0300, Ilias Apalodimas wrote:
> Currently we don't support sha384/512 for the X.509
> certificate To-Be-Signed contents. Moreover if we come across such a
> hash we skip the check and approve the image, although the image
> might needs to be rejected.
Are you sure? You seem to be talking about efi_signature_check_revocation() here.
Please be more specific.
> It's worth noting here that efi_hash_regions() can now be reused from
> efi_signature_lookup_digest() and add sha348/512 support there as well
>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> ---
> include/efi_api.h | 6 ++++
> lib/efi_loader/efi_signature.c | 62 ++++++++++++++++++++++++++--------
> 2 files changed, 53 insertions(+), 15 deletions(-)
>
> diff --git a/include/efi_api.h b/include/efi_api.h
> index 982c2001728d..b9a04958f9ba 100644
> --- a/include/efi_api.h
> +++ b/include/efi_api.h
> @@ -1873,6 +1873,12 @@ struct efi_system_resource_table {
> #define EFI_CERT_X509_SHA256_GUID \
> EFI_GUID(0x3bd2a492, 0x96c0, 0x4079, 0xb4, 0x20, \
> 0xfc, 0xf9, 0x8e, 0xf1, 0x03, 0xed)
> +#define EFI_CERT_X509_SHA384_GUID \
> + EFI_GUID(0x7076876e, 0x80c2, 0x4ee6, \
> + 0xaa, 0xd2, 0x28, 0xb3, 0x49, 0xa6, 0x86, 0x5b)
> +#define EFI_CERT_X509_SHA512_GUID \
> + EFI_GUID(0x446dbf63, 0x2502, 0x4cda, \
> + 0xbc, 0xfa, 0x24, 0x65, 0xd2, 0xb0, 0xfe, 0x9d)
> #define EFI_CERT_TYPE_PKCS7_GUID \
> EFI_GUID(0x4aafd29d, 0x68df, 0x49ee, 0x8a, 0xa9, \
> 0x34, 0x7d, 0x37, 0x56, 0x65, 0xa7)
> diff --git a/lib/efi_loader/efi_signature.c b/lib/efi_loader/efi_signature.c
> index 79ed077ae7dd..392eae6c0d64 100644
> --- a/lib/efi_loader/efi_signature.c
> +++ b/lib/efi_loader/efi_signature.c
> @@ -24,6 +24,8 @@ const efi_guid_t efi_guid_sha256 = EFI_CERT_SHA256_GUID;
> const efi_guid_t efi_guid_cert_rsa2048 = EFI_CERT_RSA2048_GUID;
> const efi_guid_t efi_guid_cert_x509 = EFI_CERT_X509_GUID;
> const efi_guid_t efi_guid_cert_x509_sha256 = EFI_CERT_X509_SHA256_GUID;
> +const efi_guid_t efi_guid_cert_x509_sha384 = EFI_CERT_X509_SHA384_GUID;
> +const efi_guid_t efi_guid_cert_x509_sha512 = EFI_CERT_X509_SHA512_GUID;
Please add, at least, one test case along with this patch
if you want to expand the coverage of UEFI specification.
> const efi_guid_t efi_guid_cert_type_pkcs7 = EFI_CERT_TYPE_PKCS7_GUID;
>
> static u8 pkcs7_hdr[] = {
> @@ -124,23 +126,32 @@ struct pkcs7_message *efi_parse_pkcs7_header(const void *buf,
> * Return: true on success, false on error
> */
> static bool efi_hash_regions(struct image_region *regs, int count,
> - void **hash, size_t *size)
> + void **hash, size_t size)
It would be better to hand off either an algorithm name or a corresponding guid
rather than "size" as an identification of hash algo for extending this function
in the future.
> {
> + char hash_algo[16];
> + int ret;
> +
> + /* basic sanity checking */
> + if (!size)
> + return false;
> +
> + ret = snprintf(hash_algo, sizeof(hash_algo), "sha%ld", size * 8);
> + if (ret >= sizeof(hash_algo))
> + return false;
> +
> if (!*hash) {
> - *hash = calloc(1, SHA256_SUM_LEN);
> + *hash = calloc(1, size);
> if (!*hash) {
> EFI_PRINT("Out of memory\n");
> return false;
> }
> }
> - if (size)
> - *size = SHA256_SUM_LEN;
>
> - hash_calculate("sha256", regs, count, *hash);
> + hash_calculate(hash_algo, regs, count, *hash);
> #ifdef DEBUG
> EFI_PRINT("hash calculated:\n");
> print_hex_dump(" ", DUMP_PREFIX_OFFSET, 16, 1,
> - *hash, SHA256_SUM_LEN, false);
> + *hash, size, false);
> #endif
>
> return true;
> @@ -190,7 +201,7 @@ bool efi_signature_lookup_digest(struct efi_image_regions *regs,
> struct efi_signature_store *siglist;
> struct efi_sig_data *sig_data;
> void *hash = NULL;
> - size_t size = 0;
> + size_t size = SHA256_SUM_LEN;
> bool found = false;
> bool hash_done = false;
>
> @@ -216,7 +227,7 @@ bool efi_signature_lookup_digest(struct efi_image_regions *regs,
> continue;
>
> if (!hash_done &&
> - !efi_hash_regions(regs->reg, regs->num, &hash, &size)) {
> + !efi_hash_regions(regs->reg, regs->num, &hash, size)) {
> EFI_PRINT("Digesting an image failed\n");
> break;
> }
> @@ -263,7 +274,7 @@ static bool efi_lookup_certificate(struct x509_certificate *cert,
> struct efi_sig_data *sig_data;
> struct image_region reg[1];
> void *hash = NULL, *hash_tmp = NULL;
> - size_t size = 0;
> + size_t size = SHA256_SUM_LEN;
> bool found = false;
>
> EFI_PRINT("%s: Enter, %p, %p\n", __func__, cert, db);
> @@ -278,7 +289,7 @@ static bool efi_lookup_certificate(struct x509_certificate *cert,
> /* calculate hash of TBSCertificate */
> reg[0].data = cert->tbs;
> reg[0].size = cert->tbs_size;
> - if (!efi_hash_regions(reg, 1, &hash, &size))
> + if (!efi_hash_regions(reg, 1, &hash, size))
> goto out;
>
> EFI_PRINT("%s: searching for %s\n", __func__, cert->subject);
> @@ -300,7 +311,7 @@ static bool efi_lookup_certificate(struct x509_certificate *cert,
> cert_tmp->subject);
> reg[0].data = cert_tmp->tbs;
> reg[0].size = cert_tmp->tbs_size;
> - if (!efi_hash_regions(reg, 1, &hash_tmp, NULL))
> + if (!efi_hash_regions(reg, 1, &hash_tmp, size))
> goto out;
>
> x509_free_certificate(cert_tmp);
> @@ -377,6 +388,26 @@ out:
> return verified;
> }
>
> +/** guid_to_sha_len - return the sha size in bytes for a given guid
> + * used of EFI security databases
> + *
> + * @guid: guid to check
> + *
> + * Return: len or 0 if no match is found
> + */
> +static int guid_to_sha_len(efi_guid_t *guid)
> +{
> + int size = 0;
> +
> + if (!guidcmp(guid, &efi_guid_cert_x509_sha256))
> + size = SHA256_SUM_LEN;
> + else if (!guidcmp(guid, &efi_guid_cert_x509_sha384))
> + size = SHA384_SUM_LEN;
> + else if (!guidcmp(guid, &efi_guid_cert_x509_sha512))
> + size = SHA512_SUM_LEN;
> +
> + return size;
> +}
> /**
> * efi_signature_check_revocation - check revocation with dbx
> * @sinfo: Signer's info
> @@ -400,7 +431,7 @@ static bool efi_signature_check_revocation(struct pkcs7_signed_info *sinfo,
> struct efi_sig_data *sig_data;
> struct image_region reg[1];
> void *hash = NULL;
> - size_t size = 0;
> + size_t size = SHA256_SUM_LEN;
> time64_t revoc_time;
> bool revoked = false;
>
> @@ -411,13 +442,14 @@ static bool efi_signature_check_revocation(struct pkcs7_signed_info *sinfo,
>
> EFI_PRINT("Checking revocation against %s\n", cert->subject);
> for (siglist = dbx; siglist; siglist = siglist->next) {
> - if (guidcmp(&siglist->sig_type, &efi_guid_cert_x509_sha256))
> + size = guid_to_sha_len(&siglist->sig_type);
> + if (!size)
Even with this change,
> Moreover if we come across such a
> hash we skip the check and approve the image, although the image
> might needs to be rejected.
the behavior won't be fixed.
-Takahiro Akashi
> continue;
>
> /* calculate hash of TBSCertificate */
> reg[0].data = cert->tbs;
> reg[0].size = cert->tbs_size;
> - if (!efi_hash_regions(reg, 1, &hash, &size))
> + if (!efi_hash_regions(reg, 1, &hash, size))
> goto out;
>
> for (sig_data = siglist->sig_data_list; sig_data;
> @@ -500,7 +532,7 @@ bool efi_signature_verify(struct efi_image_regions *regs,
> */
> if (!msg->data &&
> !efi_hash_regions(regs->reg, regs->num,
> - (void **)&sinfo->sig->digest, NULL)) {
> + (void **)&sinfo->sig->digest, SHA256_SUM_LEN)) {
> EFI_PRINT("Digesting an image failed\n");
> goto out;
> }
> --
> 2.32.0
>
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