x86/kaslr: Make command line handling safer

Handle the possibility that the command line is NULL.

Replace open-coded strlen with a function call.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200727230801.3468620-2-nivedita@alum.mit.edu

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index d7408af..e0f69f3 100644 (file)
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -268,15 +268,19 @@ static void parse_gb_huge_pages(char *param, char *val)
 static void handle_mem_options(void)
 {
        char *args = (char *)get_cmd_line_ptr();
-       size_t len = strlen((char *)args);
+       size_t len;
        char *tmp_cmdline;
        char *param, *val;
        u64 mem_size;
 
+       if (!args)
+               return;
+
        if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
                !strstr(args, "hugepages"))
                return;
 
+       len = strlen(args);
        tmp_cmdline = malloc(len + 1);
        if (!tmp_cmdline)
                error("Failed to allocate space for tmp_cmdline");
@@ -399,8 +403,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
 {
        unsigned long init_size = boot_params->hdr.init_size;
        u64 initrd_start, initrd_size;
-       u64 cmd_line, cmd_line_size;
-       char *ptr;
+       unsigned long cmd_line, cmd_line_size;
 
        /*
         * Avoid the region that is unsafe to overlap during
@@ -421,16 +424,15 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
        /* No need to set mapping for initrd, it will be handled in VO. */
 
        /* Avoid kernel command line. */
-       cmd_line  = (u64)boot_params->ext_cmd_line_ptr << 32;
-       cmd_line |= boot_params->hdr.cmd_line_ptr;
+       cmd_line = get_cmd_line_ptr();
        /* Calculate size of cmd_line. */
-       ptr = (char *)(unsigned long)cmd_line;
-       for (cmd_line_size = 0; ptr[cmd_line_size++];)
-               ;
-       mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
-       mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
-       add_identity_map(mem_avoid[MEM_AVOID_CMDLINE].start,
-                        mem_avoid[MEM_AVOID_CMDLINE].size);
+       if (cmd_line) {
+               cmd_line_size = strlen((char *)cmd_line) + 1;
+               mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
+               mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
+               add_identity_map(mem_avoid[MEM_AVOID_CMDLINE].start,
+                                mem_avoid[MEM_AVOID_CMDLINE].size);
+       }
 
        /* Avoid boot parameters. */
        mem_avoid[MEM_AVOID_BOOTPARAMS].start = (unsigned long)boot_params;