[PATCHv7 08/13] kexec_file: Factor out routine to find a symbol in ELF

[Pingfan Liu <piliu@redhat.com>]

The routine to search a symbol in ELF can be shared, so split it out.

Signed-off-by: Pingfan Liu <piliu@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Philipp Rudo <prudo@redhat.com>
To: kexec@lists.infradead.org
---
 kernel/kexec_file.c     | 61 +++++++++++++++++++++++++++++++++++++++++
 kernel/kexec_internal.h |  1 +
 2 files changed, 62 insertions(+)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index aca265034b4ed..15857a56e6278 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -902,6 +902,51 @@ static int kexec_calculate_store_digests(struct kimage *image)
 	return ret;
 }
 
+#if defined(CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY) || defined(CONFIG_KEXEC_BPF)
+const Elf_Sym *elf_find_symbol(const Elf_Ehdr *ehdr, const char *name)
+{
+	const Elf_Shdr *sechdrs;
+	const Elf_Sym *syms;
+	const char *strtab;
+	int i, k;
+
+	sechdrs = (void *)ehdr + ehdr->e_shoff;
+
+	for (i = 0; i < ehdr->e_shnum; i++) {
+		if (sechdrs[i].sh_type != SHT_SYMTAB)
+			continue;
+
+		if (sechdrs[i].sh_link >= ehdr->e_shnum)
+			/* Invalid strtab section number */
+			continue;
+		strtab = (void *)ehdr + sechdrs[sechdrs[i].sh_link].sh_offset;
+		syms = (void *)ehdr + sechdrs[i].sh_offset;
+
+		/* Go through symbols for a match */
+		for (k = 0; k < sechdrs[i].sh_size/sizeof(Elf_Sym); k++) {
+			if (ELF_ST_BIND(syms[k].st_info) != STB_GLOBAL)
+				continue;
+
+			if (strcmp(strtab + syms[k].st_name, name) != 0)
+				continue;
+
+			if (syms[k].st_shndx == SHN_UNDEF ||
+			    syms[k].st_shndx >= ehdr->e_shnum) {
+				pr_debug("Symbol: %s has bad section index %d.\n",
+						name, syms[k].st_shndx);
+				return NULL;
+			}
+
+			/* Found the symbol we are looking for */
+			return &syms[k];
+		}
+	}
+
+	return NULL;
+}
+
+#endif
+
 #ifdef CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY
 /*
  * kexec_purgatory_find_symbol - find a symbol in the purgatory
@@ -1221,6 +1266,22 @@ int kexec_load_purgatory(struct kimage *image, struct kexec_buf *kbuf)
 	return ret;
 }
 
+/*
+ * kexec_purgatory_find_symbol - find a symbol in the purgatory
+ * @pi:		Purgatory to search in.
+ * @name:	Name of the symbol.
+ *
+ * Return: pointer to symbol in read-only symtab on success, NULL on error.
+ */
+static const Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
+						  const char *name)
+{
+	if (!pi->ehdr)
+		return NULL;
+
+	return elf_find_symbol(pi->ehdr, name);
+}
+
 void *kexec_purgatory_get_symbol_addr(struct kimage *image, const char *name)
 {
 	struct purgatory_info *pi = &image->purgatory_info;
diff --git a/kernel/kexec_internal.h b/kernel/kexec_internal.h
index 731ff02110b3c..224f09188db23 100644
--- a/kernel/kexec_internal.h
+++ b/kernel/kexec_internal.h
@@ -40,6 +40,7 @@ void kimage_file_post_load_cleanup(struct kimage *image);
 extern char kexec_purgatory[];
 extern size_t kexec_purgatory_size;
 extern int decompose_kexec_image(struct kimage *image, int extended_fd);
+extern const Elf_Sym *elf_find_symbol(const Elf_Ehdr *ehdr, const char *name);
 #else /* CONFIG_KEXEC_FILE */
 static inline void kimage_file_post_load_cleanup(struct kimage *image) { }
 #endif /* CONFIG_KEXEC_FILE */
-- 
2.49.0