[PATCH v1 05/14] efi: loader: pe: add helpers for the image size and a named section

[Johannes Schneider]

An EFI image may be read from a raw partition far larger than the
image. Add efi_pe_image_size(), which derives the size as written from
the section and certificate tables and needs only the headers;
efi_pe_file_size(), the same for a buffer holding the whole image; and
efi_pe_find_section() and efi_pe_find_next_section(), which return the
file data of the first or the next section of a name.

All of them parse untrusted images through efi_image_parse_header(). For
efi_pe_image_size() to work on a buffer holding only the headers, the
check that the certificate table lies within the buffer moves from
efi_image_parse_header() to efi_image_parse(), the only caller that
reads the table.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Johannes Schneider <johannes.schneider at leica-geosystems.com>
---
 efi/loader/pe.c         | 116 +++++++++++++++++++++++++++++++++++++++-
 include/efi/loader/pe.h |   7 +++
 2 files changed, 121 insertions(+), 2 deletions(-)

diff --git a/efi/loader/pe.c b/efi/loader/pe.c
index 4b7874fe2a..827b50378c 100644
--- a/efi/loader/pe.c
+++ b/efi/loader/pe.c
@@ -507,8 +507,6 @@ static bool efi_image_parse_header(void *efi, size_t len,
 		return false;
 	if (!pe_range_ok(len, 0, *header_sizep))
 		return false;
-	if (*authszp && !pe_range_ok(len, *authoffp, *authszp))
-		return false;
 
 	if (!pe_range_ok(len, 0, csum_off) ||
 	    !pe_range_ok(len, subsys_off, 0) ||
@@ -570,6 +568,8 @@ bool efi_image_parse(void *efi, size_t len, struct efi_image_regions **regp,
 	if (!efi_image_parse_header(efi, len, &nt, &sections, &header_size,
 				    &align, &authoff, &authsz))
 		return false;
+	if (authsz && !pe_range_ok(len, authoff, authsz))
+		return false;
 
 	/*
 	 * Count maximum number of regions to be digested.
@@ -780,6 +780,118 @@ static int fuzz_pe(const u8 *data, size_t size)
 }
 fuzz_test("pe", fuzz_pe);
 
+/**
+ * efi_pe_image_size() - size of a PE image as written to storage
+ * @efi:	buffer holding at least the PE headers
+ * @len:	size of @efi
+ *
+ * Return: the end of the last section or of the certificate table, whichever
+ * is further, which may lie beyond @len, or 0 if @efi holds no valid PE
+ * headers.
+ */
+size_t efi_pe_image_size(void *efi, size_t len)
+{
+	IMAGE_NT_HEADERS32 *nt;
+	IMAGE_SECTION_HEADER *sections;
+	u32 header_size, align, authoff, authsz;
+	size_t size, end;
+	int i;
+
+	if (!efi_image_parse_header(efi, len, &nt, &sections, &header_size,
+				    &align, &authoff, &authsz))
+		return 0;
+
+	size = header_size;
+
+	for (i = 0; i < nt->FileHeader.sections; i++) {
+		if (check_add_overflow((size_t)sections[i].PointerToRawData,
+				       (size_t)sections[i].SizeOfRawData, &end))
+			return 0;
+		size = max(size, end);
+	}
+
+	if (check_add_overflow((size_t)authoff, (size_t)authsz, &end))
+		return 0;
+
+	return max(size, end);
+}
+
+/**
+ * efi_pe_file_size() - size of a PE image held completely in a buffer
+ * @efi:	buffer holding the image
+ * @len:	size of @efi, possibly larger than the image
+ *
+ * Return: efi_pe_image_size(), or 0 if the image does not fit into @len.
+ */
+size_t efi_pe_file_size(void *efi, size_t len)
+{
+	size_t size = efi_pe_image_size(efi, len);
+
+	return size <= len ? size : 0;
+}
+
+/**
+ * efi_pe_find_next_section() - locate the next section of a name
+ * @efi:	PE image
+ * @len:	size of @efi
+ * @name:	section name, at most 8 characters
+ * @size:	returns the size of the section data
+ * @index:	section table index to start at; set past the section found
+ *
+ * Return: pointer to the section data in @efi, or NULL if there is none.
+ */
+const void *efi_pe_find_next_section(void *efi, size_t len, const char *name,
+				     size_t *size, int *index)
+{
+	IMAGE_NT_HEADERS32 *nt;
+	IMAGE_SECTION_HEADER *sections;
+	u32 header_size, align, authoff, authsz;
+	size_t namelen = strlen(name), sz;
+	int i;
+
+	if (namelen > 8)
+		return NULL;
+
+	if (!efi_image_parse_header(efi, len, &nt, &sections, &header_size,
+				    &align, &authoff, &authsz))
+		return NULL;
+
+	for (i = *index; i < nt->FileHeader.sections; i++) {
+		if (memcmp(sections[i].Name, name, namelen) ||
+		    (namelen < 8 && sections[i].Name[namelen]))
+			continue;
+
+		sz = sections[i].Misc.VirtualSize ?: sections[i].SizeOfRawData;
+		sz = min_t(size_t, sz, sections[i].SizeOfRawData);
+		if (!pe_range_ok(len, sections[i].PointerToRawData, sz))
+			return NULL;
+
+		*size = sz;
+		*index = i + 1;
+		return efi + sections[i].PointerToRawData;
+	}
+
+	return NULL;
+}
+
+/**
+ * efi_pe_find_section() - locate a section's file data by name
+ * @efi:	PE image
+ * @len:	size of @efi
+ * @name:	section name, at most 8 characters
+ * @size:	returns the size of the section data
+ *
+ * Return: pointer to the first section's data in @efi, or NULL if there is
+ * none.
+ */
+const void *efi_pe_find_section(void *efi, size_t len, const char *name,
+				size_t *size)
+{
+	int index = 0;
+
+	return efi_pe_find_next_section(efi, len, name, size, &index);
+}
+
 #ifdef CONFIG_EFI_LOADER
 static bool efi_image_authenticate(void *efi, size_t efi_size)
 {
diff --git a/include/efi/loader/pe.h b/include/efi/loader/pe.h
index b99f517cbf..2d2a19604f 100644
--- a/include/efi/loader/pe.h
+++ b/include/efi/loader/pe.h
@@ -73,6 +73,13 @@ void *efi_prepare_aligned_image(void *efi, u64 *efi_size);
 bool efi_image_parse(void *efi, size_t len, struct efi_image_regions **regp,
 		     struct _WIN_CERTIFICATE **auth, size_t *auth_len);
 
+size_t efi_pe_image_size(void *efi, size_t len);
+size_t efi_pe_file_size(void *efi, size_t len);
+const void *efi_pe_find_next_section(void *efi, size_t len, const char *name,
+				     size_t *size, int *index);
+const void *efi_pe_find_section(void *efi, size_t len, const char *name,
+				size_t *size);
+
 /* Check if a buffer contains a PE-COFF image */
 efi_status_t efi_check_pe(void *buffer, size_t size, void **nt_header);
 /* PE loader implementation */
-- 
2.43.0