Re: [RFC PATCH] efi_loader: add sha384/512 on certificate revocation

Hi Akashi-san,

On Mon, Apr 11, 2022 at 05:31:08PM +0900, AKASHI Takahiro wrote: 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.

Arm has a security ACS testsuite [1]. The whole checking fails exactly on this bug.

...

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@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.

Sure, once the RFC is discussed

...

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.

That's exactly what happens here. There's a guid_to_sha_len() that derives the len for us. I'd rather keep this as is, since the impact on the rest of the code is minimal.

...

{

• 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.

Are there other x509_shaxxx for dbx that the spec describes?

-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

[1] https://github.com/ARM-software/arm-systemready/tree/security-extension-acs

Thanks /Ilias