[PATCH v2 08/10] efi/libstub: Make efi_remap_image() return efi_status_t

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

efi_remap_image() uses the EFI Memory Attributes Protocol to remap code
and data regions with the appropriate permissions. This could fail for a
variety of regions, all of which are currently ignored.

So relay the failure status code if any occur when invoking the
protocol. Locating the protocol itself is allowed to fail, as remapping
the image is likely unnecessary in the first place if the protocol does
not exist.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/libstub/efi-stub-helper.c | 15 ++++++++++-----
 drivers/firmware/efi/libstub/efistub.h         |  4 ++--
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 8e43eb3f418b..e50deec99686 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -697,9 +697,11 @@ efi_status_t efi_wait_for_key(unsigned long usec, efi_input_key_t *key)
  * region of the loaded image read-only/executable, and the remainder
  * read-write/non-executable. The code region is assumed to start at the base
  * of the image, and will therefore cover the PE/COFF header as well.
+ *
+ * Return: EFI_SUCCESS on success, other EFI status codes on failure.
  */
-void efi_remap_image(unsigned long image_base, unsigned alloc_size,
-		     unsigned long code_size)
+efi_status_t efi_remap_image(unsigned long image_base, unsigned alloc_size,
+			     unsigned long code_size)
 {
 	static efi_guid_t guid = EFI_MEMORY_ATTRIBUTE_PROTOCOL_GUID;
 	efi_memory_attribute_protocol_t *memattr;
@@ -710,10 +712,12 @@ void efi_remap_image(unsigned long image_base, unsigned alloc_size,
 	 * If the firmware implements the EFI_MEMORY_ATTRIBUTE_PROTOCOL, let's
 	 * invoke it to remap the text/rodata region of the decompressed image
 	 * as read-only and the data/bss region as non-executable.
+	 * Don't bother if the protocol does not exist: it means all memory is
+	 * read-write-exec anyway.
 	 */
 	status = efi_bs_call(locate_protocol, &guid, NULL, (void **)&memattr);
 	if (status != EFI_SUCCESS)
-		return;
+		return EFI_SUCCESS;
 
 	// Get the current attributes for the entire region
 	status = memattr->get_memory_attributes(memattr, image_base,
@@ -721,7 +725,7 @@ void efi_remap_image(unsigned long image_base, unsigned alloc_size,
 	if (status != EFI_SUCCESS) {
 		efi_warn("Failed to retrieve memory attributes for image region: 0x%lx\n",
 			 status);
-		return;
+		return status;
 	}
 
 	// Mark the code region as read-only
@@ -729,7 +733,7 @@ void efi_remap_image(unsigned long image_base, unsigned alloc_size,
 						EFI_MEMORY_RO);
 	if (status != EFI_SUCCESS) {
 		efi_warn("Failed to remap code region read-only\n");
-		return;
+		return status;
 	}
 
 	// If the entire region was already mapped as non-exec, clear the
@@ -749,4 +753,5 @@ void efi_remap_image(unsigned long image_base, unsigned alloc_size,
 		if (status != EFI_SUCCESS)
 			efi_warn("Failed to remap data region non-executable\n");
 	}
+	return status;
 }
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index 394796472cc0..e2a9339f3e2c 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -1283,8 +1283,8 @@ struct efi_smbios_type4_record {
 const u8 *__efi_get_smbios_string(const struct efi_smbios_record *record,
 				  const u8 *offset);
 
-void efi_remap_image(unsigned long image_base, unsigned alloc_size,
-		     unsigned long code_size);
+efi_status_t efi_remap_image(unsigned long image_base, unsigned alloc_size,
+			     unsigned long code_size);
 efi_status_t efi_kaslr_relocate_kernel(unsigned long *image_addr,
 				       unsigned long *reserve_addr,
 				       unsigned long *reserve_size,
-- 
2.56.0.542.g3ef89b7020-goog