efi/libstub: Use snprintf with %ls to convert the command line

Now we can use snprintf to do the UTF-16 to UTF-8 translation for the
command line.

Drop the special "zero" trick to handle an empty command line. This was
unnecessary even before this since with options_chars == 0,
efi_utf16_to_utf8 would not have accessed options at all. snprintf won't
access it either with a precision of 0.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200518190716.751506-25-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 4d544f3954037c1989625a1953caa66643609319..9fb107e9355bc5b7ddcbdffed073e1ae5b2334b8 100644 (file)
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -205,46 +205,6 @@ efi_status_t efi_parse_options(char const *cmdline)
        return EFI_SUCCESS;
 }
 
-/*
- * Convert an UTF-16 string, not necessarily null terminated, to UTF-8.
- */
-static u8 *efi_utf16_to_utf8(u8 *dst, const u16 *src, int n)
-{
-       unsigned int c;
-
-       while (n--) {
-               c = *src++;
-               if (n && c >= 0xd800 && c <= 0xdbff &&
-                   *src >= 0xdc00 && *src <= 0xdfff) {
-                       c = 0x10000 + ((c & 0x3ff) << 10) + (*src & 0x3ff);
-                       src++;
-                       n--;
-               }
-               if (c >= 0xd800 && c <= 0xdfff)
-                       c = 0xfffd; /* Unmatched surrogate */
-               if (c < 0x80) {
-                       *dst++ = c;
-                       continue;
-               }
-               if (c < 0x800) {
-                       *dst++ = 0xc0 + (c >> 6);
-                       goto t1;
-               }
-               if (c < 0x10000) {
-                       *dst++ = 0xe0 + (c >> 12);
-                       goto t2;
-               }
-               *dst++ = 0xf0 + (c >> 18);
-               *dst++ = 0x80 + ((c >> 12) & 0x3f);
-       t2:
-               *dst++ = 0x80 + ((c >> 6) & 0x3f);
-       t1:
-               *dst++ = 0x80 + (c & 0x3f);
-       }
-
-       return dst;
-}
-
 /*
  * Convert the unicode UEFI command line to ASCII to pass to kernel.
  * Size of memory allocated return in *cmd_line_len.
@@ -254,18 +214,15 @@ char *efi_convert_cmdline(efi_loaded_image_t *image,
                          int *cmd_line_len, unsigned long max_addr)
 {
        const u16 *s2;
-       u8 *s1 = NULL;
        unsigned long cmdline_addr = 0;
-       int load_options_chars = efi_table_attr(image, load_options_size) / 2;
+       int options_chars = efi_table_attr(image, load_options_size) / 2;
        const u16 *options = efi_table_attr(image, load_options);
        int options_bytes = 0;  /* UTF-8 bytes */
-       int options_chars = 0;  /* UTF-16 chars */
        efi_status_t status;
-       u16 zero = 0;
 
        if (options) {
                s2 = options;
-               while (options_chars < load_options_chars) {
+               while (options_chars--) {
                        u16 c = *s2++;
 
                        if (c == L'\0' || c == L'\n')
@@ -276,7 +233,6 @@ char *efi_convert_cmdline(efi_loaded_image_t *image,
                         * The first part handles everything in the BMP.
                         */
                        options_bytes += 1 + (c >= 0x80) + (c >= 0x800);
-                       options_chars++;
                        /*
                         * Add one more byte for valid surrogate pairs. Invalid
                         * surrogates will be replaced with 0xfffd and take up
@@ -288,35 +244,25 @@ char *efi_convert_cmdline(efi_loaded_image_t *image,
                                 * we must ignore it since we can't access the
                                 * low surrogate.
                                 */
-                               if (options_chars == load_options_chars) {
+                               if (!options_chars) {
                                        options_bytes -= 3;
-                                       options_chars--;
-                                       break;
                                } else if ((*s2 & 0xfc00) == 0xdc00) {
                                        options_bytes++;
-                                       options_chars++;
+                                       options_chars--;
                                        s2++;
                                }
                        }
                }
        }
 
-       if (!options_chars) {
-               /* No command line options, so return empty string*/
-               options = &zero;
-       }
-
        options_bytes++;        /* NUL termination */
 
        status = efi_allocate_pages(options_bytes, &cmdline_addr, max_addr);
        if (status != EFI_SUCCESS)
                return NULL;
 
-       s1 = (u8 *)cmdline_addr;
-       s2 = (const u16 *)options;
-
-       s1 = efi_utf16_to_utf8(s1, s2, options_chars);
-       *s1 = '\0';
+       snprintf((char *)cmdline_addr, options_bytes, "%.*ls",
+                options_bytes - 1, options);
 
        *cmd_line_len = options_bytes;
        return (char *)cmdline_addr;