kexec_file: use SHA-256 library API instead of crypto_shash API

JIRA: https://issues.redhat.com/browse/RHEL-114162

Upstream Status: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

Conflict: there's conflict in line 776 of kernel/kexec_file.c. I haven't
got the reason why it has conflict. Seems it's caused by upstream
merging and the mess is produced. Have to edit it manually to grab that
hunk.

commit f7a667a
Author: Eric Biggers <ebiggers@google.com>
Date:   Mon Apr 28 11:57:20 2025 -0700

    kexec_file: use SHA-256 library API instead of crypto_shash API

    This user of SHA-256 does not support any other algorithm, so the
    crypto_shash abstraction provides no value.  Just use the SHA-256 library
    API instead, which is much simpler and easier to use.

    Tested with '/sbin/kexec --kexec-file-syscall'.

    Link: https://lkml.kernel.org/r/20250428185721.844686-1-ebiggers@kernel.org
    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Cc: Baoquan He <bhe@redhat.com>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    Cc: Dave Young <dyoung@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Baoquan He <bhe@redhat.com>

Author: Baoquan He

kernel/Kconfig.kexec

@@ -38,8 +38,7 @@ config KEXEC
 config KEXEC_FILE
 	bool "Enable kexec file based system call"
 	depends on ARCH_SUPPORTS_KEXEC_FILE
-	select CRYPTO
-	select CRYPTO_SHA256
+	select CRYPTO_LIB_SHA256
 	select KEXEC_CORE
 	help
 	  This is new version of kexec system call. This system call is

kernel/kexec_file.c

@@ -19,7 +19,6 @@
 #include <linux/list.h>
 #include <linux/fs.h>
 #include <linux/ima.h>
-#include <crypto/hash.h>
 #include <crypto/sha2.h>
 #include <linux/elf.h>
 #include <linux/elfcore.h>
@@ -736,11 +735,10 @@ int kexec_add_buffer(struct kexec_buf *kbuf)
 /* Calculate and store the digest of segments */
 static int kexec_calculate_store_digests(struct kimage *image)
 {
-	struct crypto_shash *tfm;
-	struct shash_desc *desc;
+	struct sha256_state state;
 	int ret = 0, i, j, zero_buf_sz, sha_region_sz;
-	size_t desc_size, nullsz;
-	char *digest;
+	size_t nullsz;
+	u8 digest[SHA256_DIGEST_SIZE];
 	void *zero_buf;
 	struct kexec_sha_region *sha_regions;
 	struct purgatory_info *pi = &image->purgatory_info;
@@ -751,37 +749,12 @@ static int kexec_calculate_store_digests(struct kimage *image)
 	zero_buf = __va(page_to_pfn(ZERO_PAGE(0)) << PAGE_SHIFT);
 	zero_buf_sz = PAGE_SIZE;
 
-	tfm = crypto_alloc_shash("sha256", 0, 0);
-	if (IS_ERR(tfm)) {
-		ret = PTR_ERR(tfm);
-		goto out;
-	}
-
-	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
-	desc = kzalloc(desc_size, GFP_KERNEL);
-	if (!desc) {
-		ret = -ENOMEM;
-		goto out_free_tfm;
-	}
-
 	sha_region_sz = KEXEC_SEGMENT_MAX * sizeof(struct kexec_sha_region);
 	sha_regions = vzalloc(sha_region_sz);
-	if (!sha_regions) {
-		ret = -ENOMEM;
-		goto out_free_desc;
-	}
-
-	desc->tfm   = tfm;
-
-	ret = crypto_shash_init(desc);
-	if (ret < 0)
-		goto out_free_sha_regions;
+	if (!sha_regions)
+		return -ENOMEM;
 
-	digest = kzalloc(SHA256_DIGEST_SIZE, GFP_KERNEL);
-	if (!digest) {
-		ret = -ENOMEM;
-		goto out_free_sha_regions;
-	}
+	sha256_init(&state);
 
 	for (j = i = 0; i < image->nr_segments; i++) {
 		struct kexec_segment *ksegment;
@@ -807,10 +780,7 @@ static int kexec_calculate_store_digests(struct kimage *image)
 		if (check_ima_segment_index(image, i))
 			continue;
 
-		ret = crypto_shash_update(desc, ksegment->kbuf,
-					  ksegment->bufsz);
-		if (ret)
-			break;
+		sha256_update(&state, ksegment->kbuf, ksegment->bufsz);
 
 		/*
 		 * Assume rest of the buffer is filled with zero and
@@ -822,44 +792,26 @@ static int kexec_calculate_store_digests(struct kimage *image)
 
 			if (bytes > zero_buf_sz)
 				bytes = zero_buf_sz;
-			ret = crypto_shash_update(desc, zero_buf, bytes);
-			if (ret)
-				break;
+			sha256_update(&state, zero_buf, bytes);
 			nullsz -= bytes;
 		}
 
-		if (ret)
-			break;
-
 		sha_regions[j].start = ksegment->mem;
 		sha_regions[j].len = ksegment->memsz;
 		j++;
 	}
 
-	if (!ret) {
-		ret = crypto_shash_final(desc, digest);
-		if (ret)
-			goto out_free_digest;
-		ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha_regions",
-						     sha_regions, sha_region_sz, 0);
-		if (ret)
-			goto out_free_digest;
+	sha256_final(&state, digest);
 
-		ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha256_digest",
-						     digest, SHA256_DIGEST_SIZE, 0);
-		if (ret)
-			goto out_free_digest;
-	}
+	ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha_regions",
+					     sha_regions, sha_region_sz, 0);
+	if (ret)
+		goto out_free_sha_regions;
 
-out_free_digest:
-	kfree(digest);
+	ret = kexec_purgatory_get_set_symbol(image, "purgatory_sha256_digest",
+					     digest, SHA256_DIGEST_SIZE, 0);
 out_free_sha_regions:
 	vfree(sha_regions);
-out_free_desc:
-	kfree(desc);
-out_free_tfm:
-	kfree(tfm);
-out:
 	return ret;
 }