pc-bios/s390-ccw: El Torito 16-bit boot image size field workaround

Because of El Torito spec flaw boot image size needs to be verified.

Boot catalog entry size field has 16-bit width, and specifies size
in 512-byte units.

Thus, boot image size cannot exceed 32M.

We actually search for the file to get the file size.

This is done by scanning the ISO directory tree for the ISO block number
and reading the file size from the directory entry.

Signed-off-by: Maxim Samoylov <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>

pc-bios/s390-ccw/bootmap.c

@@ -462,6 +462,87 @@ static bool is_iso_bc_entry_compatible(IsoBcSection *s)
     return !_memcmp(magic_sec + 8, linux_s390_magic, 24);
 }
 
+/* Location of the current sector of the directory */
+static uint32_t sec_loc[ISO9660_MAX_DIR_DEPTH];
+/* Offset in the current sector of the directory */
+static uint32_t sec_offset[ISO9660_MAX_DIR_DEPTH];
+/* Remained directory space in bytes */
+static uint32_t dir_rem[ISO9660_MAX_DIR_DEPTH];
+
+static inline uint32_t iso_get_file_size(uint32_t load_rba)
+{
+    IsoVolDesc *vd = (IsoVolDesc *)sec;
+    IsoDirHdr *cur_record = &vd->vd.primary.rootdir;
+    uint8_t *temp = sec + ISO_SECTOR_SIZE;
+    int level = 0;
+
+    read_iso_sector(ISO_PRIMARY_VD_SECTOR, sec,
+                    "Failed to read ISO primary descriptor");
+    sec_loc[0] = iso_733_to_u32(cur_record->ext_loc);
+    dir_rem[0] = 0;
+    sec_offset[0] = 0;
+
+    while (level >= 0) {
+        IPL_assert(sec_offset[level] <= ISO_SECTOR_SIZE,
+                   "Directory tree structure violation");
+
+        cur_record = (IsoDirHdr *)(temp + sec_offset[level]);
+
+        if (sec_offset[level] == 0) {
+            read_iso_sector(sec_loc[level], temp,
+                            "Failed to read ISO directory");
+            if (dir_rem[level] == 0) {
+                /* Skip self and parent records */
+                dir_rem[level] = iso_733_to_u32(cur_record->data_len) -
+                                 cur_record->dr_len;
+                sec_offset[level] += cur_record->dr_len;
+
+                cur_record = (IsoDirHdr *)(temp + sec_offset[level]);
+                dir_rem[level] -= cur_record->dr_len;
+                sec_offset[level] += cur_record->dr_len;
+                continue;
+            }
+        }
+
+        if (!cur_record->dr_len || sec_offset[level] == ISO_SECTOR_SIZE) {
+            /* Zero-padding and/or the end of current sector */
+            dir_rem[level] -= ISO_SECTOR_SIZE - sec_offset[level];
+            sec_offset[level] = 0;
+            sec_loc[level]++;
+        } else {
+            /* The directory record is valid */
+            if (load_rba == iso_733_to_u32(cur_record->ext_loc)) {
+                return iso_733_to_u32(cur_record->data_len);
+            }
+
+            dir_rem[level] -= cur_record->dr_len;
+            sec_offset[level] += cur_record->dr_len;
+
+            if (cur_record->file_flags & 0x2) {
+                /* Subdirectory */
+                if (level == ISO9660_MAX_DIR_DEPTH - 1) {
+                    sclp_print("ISO-9660 directory depth limit exceeded\n");
+                } else {
+                    level++;
+                    sec_loc[level] = iso_733_to_u32(cur_record->ext_loc);
+                    sec_offset[level] = 0;
+                    dir_rem[level] = 0;
+                    continue;
+                }
+            }
+        }
+
+        if (dir_rem[level] == 0) {
+            /* Nothing remaining */
+            level--;
+            read_iso_sector(sec_loc[level], temp,
+                            "Failed to read ISO directory");
+        }
+    }
+
+    return 0;
+}
+
 static void load_iso_bc_entry(IsoBcSection *load)
 {
     IsoBcSection s = *load;
@@ -470,6 +551,15 @@ static void load_iso_bc_entry(IsoBcSection *load)
      * is padded and ISO_SECTOR_SIZE bytes aligned
      */
     uint32_t blks_to_load = bswap16(s.sector_count) >> ET_SECTOR_SHIFT;
+    uint32_t real_size = iso_get_file_size(bswap32(s.load_rba));
+
+    if (real_size) {
+        /* Round up blocks to load */
+        blks_to_load = (real_size + ISO_SECTOR_SIZE - 1) / ISO_SECTOR_SIZE;
+        sclp_print("ISO boot image size verified\n");
+    } else {
+        sclp_print("ISO boot image size could not be verified\n");
+    }
 
     read_iso_boot_image(bswap32(s.load_rba),
                         (void *)((uint64_t)bswap16(s.load_segment)),

pc-bios/s390-ccw/bootmap.h

@@ -381,6 +381,11 @@ static inline uint64_t bswap64(uint64_t x)
            ((x & 0xff00000000000000ULL) >> 56);
 }
 
+static inline uint32_t iso_733_to_u32(uint64_t x)
+{
+    return (uint32_t)x;
+}
+
 #define ISO_SECTOR_SIZE 2048
 /* El Torito specifies boot image size in 512 byte blocks */
 #define ET_SECTOR_SHIFT 2
@@ -407,6 +412,8 @@ static inline void read_iso_boot_image(uint32_t block_offset, void *load_addr,
 const uint8_t el_torito_magic[] = "EL TORITO SPECIFICATION"
                                   "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
 
+#define ISO9660_MAX_DIR_DEPTH 8
+
 typedef struct IsoDirHdr {
     uint8_t dr_len;
     uint8_t ear_len;