[PATCH 1/2 v2] lib/crypto: Enable more algorithms in cert verification

[PATCH 1/2 v2] lib/crypto: Enable more algorithms in cert verification

[Ilias Apalodimas]

Right now the code explicitly limits us to sha1,256 hashes with RSA2048
encryption.  But the limitation is artificial since U-Boot supports
a wider range of algorithms.

The internal image_get_[checksum|crypto]_algo() functions expect an
argument in the format of <checksum>,<crypto>.  So let's remove the size
checking and create the needed string on the fly in order to support
more hash/signing combinations.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---
changes since v1: 
- added patch [2/2] explicitly disabling sha1
- removed a TODO comment
- added a print notifying wrt to image_get_(checksum|crypto)_algo usage
 lib/crypto/public_key.c | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/lib/crypto/public_key.c b/lib/crypto/public_key.c
index df6033cdb499..3671ed138559 100644
--- a/lib/crypto/public_key.c
+++ b/lib/crypto/public_key.c
@@ -97,6 +97,7 @@ int public_key_verify_signature(const struct public_key *pkey,
 				const struct public_key_signature *sig)
 {
 	struct image_sign_info info;
+	char algo[256];
 	int ret;
 
 	pr_devel("==>%s()\n", __func__);
@@ -108,30 +109,26 @@ int public_key_verify_signature(const struct public_key *pkey,
 		return -EINVAL;
 
 	memset(&info, '\0', sizeof(info));
+	memset(algo, 0, sizeof(algo));
 	info.padding = image_get_padding_algo("pkcs-1.5");
-	/*
-	 * Note: image_get_[checksum|crypto]_algo takes a string
-	 * argument like "<checksum>,<crypto>"
-	 * TODO: support other hash algorithms
-	 */
-	if (strcmp(sig->pkey_algo, "rsa") || (sig->s_size * 8) != 2048) {
-		pr_warn("Encryption is not RSA2048: %s%d\n",
-			sig->pkey_algo, sig->s_size * 8);
-		return -ENOPKG;
-	}
-	if (!strcmp(sig->hash_algo, "sha1")) {
-		info.checksum = image_get_checksum_algo("sha1,rsa2048");
-		info.name = "sha1,rsa2048";
-	} else if (!strcmp(sig->hash_algo, "sha256")) {
-		info.checksum = image_get_checksum_algo("sha256,rsa2048");
-		info.name = "sha256,rsa2048";
-	} else {
-		pr_warn("unknown msg digest algo: %s\n", sig->hash_algo);
+	if (strcmp(sig->pkey_algo, "rsa")) {
+		pr_err("Encryption is not RSA: %s\n", sig->pkey_algo);
 		return -ENOPKG;
 	}
+	ret = snprintf(algo, sizeof(algo), "%s,%s%d", sig->hash_algo,
+		       sig->pkey_algo, sig->s_size * 8);
+
+	if (ret >= sizeof(algo))
+		return -EINVAL;
+
+	info.checksum = image_get_checksum_algo((const char *)algo);
+	info.name = (const char *)algo;
 	info.crypto = image_get_crypto_algo(info.name);
-	if (IS_ERR(info.checksum) || IS_ERR(info.crypto))
+	if (!info.checksum || !info.crypto) {
+		pr_err("<%s> not supported on image_get_(checksum|crypto)_algo()\n",
+		       algo);
 		return -ENOPKG;
+	}
 
 	info.key = pkey->key;
 	info.keylen = pkey->keylen;
-- 
2.30.2

[PATCH 2/2 v2] efi_loader: Ignore sha1 on signature verification

[Ilias Apalodimas]

Since SHA1 has know collisions disable it on EFI verification for
variables and executables

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---
 lib/efi_loader/efi_signature.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/efi_loader/efi_signature.c b/lib/efi_loader/efi_signature.c
index 6e3ee3c0c004..1903adc89ed0 100644
--- a/lib/efi_loader/efi_signature.c
+++ b/lib/efi_loader/efi_signature.c
@@ -476,6 +476,11 @@ bool efi_signature_verify(struct efi_image_regions *regs,
 		if (ret < 0 || !signer)
 			goto out;
 
+		if (!strcmp(signer->sig->hash_algo, "sha1")) {
+			pr_err("SHA1 support is disabled for EFI\n");
+			goto out;
+		}
+
 		if (sinfo->blacklisted)
 			goto out;
 
-- 
2.30.2

Re: [PATCH 2/2 v2] efi_loader: Ignore sha1 on signature verification

[Ilias Apalodimas]

Heinrich

Replying to myself here  but...

On Wed, 19 Jan 2022 at 13:54, Ilias Apalodimas
<ilias.apalodimas@linaro.org> wrote:
>
> Since SHA1 has know collisions disable it on EFI verification for
> variables and executables
>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> ---
>  lib/efi_loader/efi_signature.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/lib/efi_loader/efi_signature.c b/lib/efi_loader/efi_signature.c
> index 6e3ee3c0c004..1903adc89ed0 100644
> --- a/lib/efi_loader/efi_signature.c
> +++ b/lib/efi_loader/efi_signature.c
> @@ -476,6 +476,11 @@ bool efi_signature_verify(struct efi_image_regions *regs,
>                 if (ret < 0 || !signer)
>                         goto out;
>
> +               if (!strcmp(signer->sig->hash_algo, "sha1")) {
> +                       pr_err("SHA1 support is disabled for EFI\n");
> +                       goto out;
> +               }
> +
>                 if (sinfo->blacklisted)
>                         goto out;
>
> --
> 2.30.2
>

This patch gets the job done, but rejects the sha1 cert signed images
overall without checking db or dbx.  Since I am planning to refactor
the secure boot checking sequence a bit,  it would make more sense for
me to fix this in a less hacky way in upcoming patches.  You can ofc
pickup 1/2 whic is fixing an actual issue.

Cheers
/Ilias