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boot: Improve device_path_to_str_internal()

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The UEFI spec has a generic `Path` node representation that can be used
for device path nodes that are unknown. So we can use that instead of
giving up when we see a node other than FilePath.

This also simplifies the FilePath case by just using xasprintf(). The
code is really just a fallback for silly firmware that does not
implement EFI_DEVICE_PATH_TO_TEXT_PROTOCOL (looking at you, Apple).

The correctness of this was tested by round-tripping it through
EFI_DEVICE_PATH_FROM_TEXT_PROTOCOL, which yielded an identical device
compared to our input path.
This commit is contained in:
Jan Janssen 2023-06-18 10:54:20 +02:00
parent e53e5c0ac1
commit 78fffdea37
1 changed files with 30 additions and 29 deletions
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59
src/boot/efi/device-path-util.c
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@ -39,34 +39,41 @@ EFI_STATUS make_file_device_path(EFI_HANDLE device, const char16_t *file, EFI_DE
}
static char16_t *device_path_to_str_internal(const EFI_DEVICE_PATH *dp) {
_cleanup_free_ char16_t *str = NULL;
size_t size = 0;
for (const EFI_DEVICE_PATH *node = dp; !device_path_is_end(node);
node = device_path_next_node(node)) {
if (node->Type != MEDIA_DEVICE_PATH || node->SubType != MEDIA_FILEPATH_DP)
return NULL;
size_t path_size = node->Length;
if (path_size <= offsetof(FILEPATH_DEVICE_PATH, PathName) || path_size % sizeof(char16_t))
return NULL;
path_size -= offsetof(FILEPATH_DEVICE_PATH, PathName);
char16_t *str = NULL;
for (const EFI_DEVICE_PATH *node = dp; !device_path_is_end(node); node = device_path_next_node(node)) {
_cleanup_free_ char16_t *old = str;
str = xmalloc(size + path_size);
if (old) {
memcpy(str, old, size);
str[size / sizeof(char16_t) - 1] = '\\';
if (node->Type == END_DEVICE_PATH_TYPE && node->SubType == END_INSTANCE_DEVICE_PATH_SUBTYPE) {
str = xasprintf("%ls%s,", strempty(old), old ? "\\" : "");
continue;
}
memcpy(str + (size / sizeof(char16_t)),
((uint8_t *) node) + offsetof(FILEPATH_DEVICE_PATH, PathName),
path_size);
size += path_size;
/* Special-case this so that FilePath-only device path string look and behave nicely. */
if (node->Type == MEDIA_DEVICE_PATH && node->SubType == MEDIA_FILEPATH_DP) {
str = xasprintf("%ls%s%ls",
strempty(old),
old ? "\\" : "",
((FILEPATH_DEVICE_PATH *) node)->PathName);
continue;
}
/* Instead of coding all the different types and sub-types here we just use the
* generic node form. This function is a best-effort for firmware that does not
* provide the EFI_DEVICE_PATH_TO_TEXT_PROTOCOL after all. */
size_t size = node->Length - sizeof(EFI_DEVICE_PATH);
_cleanup_free_ char16_t *hex_data = hexdump((uint8_t *) node + sizeof(EFI_DEVICE_PATH), size);
str = xasprintf("%ls%sPath(%u,%u%s%ls)",
strempty(old),
old ? "/" : "",
node->Type,
node->SubType,
size == 0 ? "" : ",",
hex_data);
}
return TAKE_PTR(str);
return str;
}
EFI_STATUS device_path_to_str(const EFI_DEVICE_PATH *dp, char16_t **ret) {
@ -79,13 +86,7 @@ EFI_STATUS device_path_to_str(const EFI_DEVICE_PATH *dp, char16_t **ret) {
err = BS->LocateProtocol(MAKE_GUID_PTR(EFI_DEVICE_PATH_TO_TEXT_PROTOCOL), NULL, (void **) &dp_to_text);
if (err != EFI_SUCCESS) {
/* If the device path to text protocol is not available we can still do a best-effort attempt
* to convert it ourselves if we are given filepath-only device path. */
str = device_path_to_str_internal(dp);
if (!str)
return err;
*ret = TAKE_PTR(str);
*ret = device_path_to_str_internal(dp);
return EFI_SUCCESS;
}