ARC: U-boot: check arguments paranoidly

Handle U-boot arguments paranoidly:
 * don't allow to pass unknown tag.
 * try to use external device tree blob only if corresponding tag
   (TAG_DTB) is set.
 * don't check uboot_tag if kernel build with no ARC_UBOOT_SUPPORT.

NOTE:
If U-boot args are invalid we skip them and try to use embedded device
tree blob. We can't panic on invalid U-boot args as we really pass
invalid args due to bug in U-boot code.
This happens if we don't provide external DTB to U-boot and
don't set 'bootargs' U-boot environment variable (which is default
case at least for HSDK board) In that case we will pass
{r0 = 1 (bootargs in r2); r1 = 0; r2 = 0;} to linux which is invalid.

While I'm at it refactor U-boot arguments handling code.

Cc: stable@vger.kernel.org
Tested-by: Corentin LABBE <clabbe@baylibre.com>
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
index 26e33a8..1f945d0 100644 (file)
--- a/arch/arc/kernel/head.S
+++ b/arch/arc/kernel/head.S
@@ -103,9 +103,9 @@ ENTRY(stext)
 #ifdef CONFIG_ARC_UBOOT_SUPPORT
        ; Uboot - kernel ABI
        ;    r0 = [0] No uboot interaction, [1] cmdline in r2, [2] DTB in r2
-       ;    r1 = magic number (board identity, unused as of now
+       ;    r1 = magic number (always zero as of now)
        ;    r2 = pointer to uboot provided cmdline or external DTB in mem
-       ; These are handled later in setup_arch()
+       ; These are handled later in handle_uboot_args()
        st      r0, [@uboot_tag]
        st      r2, [@uboot_arg]
 #endif

diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
index def19b0..8bb1561 100644 (file)
--- a/arch/arc/kernel/setup.c
+++ b/arch/arc/kernel/setup.c
@@ -462,43 +462,80 @@ void setup_processor(void)
        arc_chk_core_config();
 }
 
-static inline int is_kernel(unsigned long addr)
+static inline bool uboot_arg_invalid(unsigned long addr)
 {
-       if (addr >= (unsigned long)_stext && addr <= (unsigned long)_end)
-               return 1;
-       return 0;
+       /*
+        * Check that it is a untranslated address (although MMU is not enabled
+        * yet, it being a high address ensures this is not by fluke)
+        */
+       if (addr < PAGE_OFFSET)
+               return true;
+
+       /* Check that address doesn't clobber resident kernel image */
+       return addr >= (unsigned long)_stext && addr <= (unsigned long)_end;
 }
 
-void __init setup_arch(char **cmdline_p)
+#define IGNORE_ARGS            "Ignore U-boot args: "
+
+/* uboot_tag values for U-boot - kernel ABI revision 0; see head.S */
+#define UBOOT_TAG_NONE         0
+#define UBOOT_TAG_CMDLINE      1
+#define UBOOT_TAG_DTB          2
+
+void __init handle_uboot_args(void)
 {
+       bool use_embedded_dtb = true;
+       bool append_cmdline = false;
+
 #ifdef CONFIG_ARC_UBOOT_SUPPORT
-       /* make sure that uboot passed pointer to cmdline/dtb is valid */
-       if (uboot_tag && is_kernel((unsigned long)uboot_arg))
-               panic("Invalid uboot arg\n");
+       /* check that we know this tag */
+       if (uboot_tag != UBOOT_TAG_NONE &&
+           uboot_tag != UBOOT_TAG_CMDLINE &&
+           uboot_tag != UBOOT_TAG_DTB) {
+               pr_warn(IGNORE_ARGS "invalid uboot tag: '%08x'\n", uboot_tag);
+               goto ignore_uboot_args;
+       }
+
+       if (uboot_tag != UBOOT_TAG_NONE &&
+            uboot_arg_invalid((unsigned long)uboot_arg)) {
+               pr_warn(IGNORE_ARGS "invalid uboot arg: '%px'\n", uboot_arg);
+               goto ignore_uboot_args;
+       }
+
+       /* see if U-boot passed an external Device Tree blob */
+       if (uboot_tag == UBOOT_TAG_DTB) {
+               machine_desc = setup_machine_fdt((void *)uboot_arg);
 
-       /* See if u-boot passed an external Device Tree blob */
-       machine_desc = setup_machine_fdt(uboot_arg);    /* uboot_tag == 2 */
-       if (!machine_desc)
+               /* external Device Tree blob is invalid - use embedded one */
+               use_embedded_dtb = !machine_desc;
+       }
+
+       if (uboot_tag == UBOOT_TAG_CMDLINE)
+               append_cmdline = true;
+
+ignore_uboot_args:
 #endif
-       {
-               /* No, so try the embedded one */
+
+       if (use_embedded_dtb) {
                machine_desc = setup_machine_fdt(__dtb_start);
                if (!machine_desc)
                        panic("Embedded DT invalid\n");
+       }
 
-               /*
-                * If we are here, it is established that @uboot_arg didn't
-                * point to DT blob. Instead if u-boot says it is cmdline,
-                * append to embedded DT cmdline.
-                * setup_machine_fdt() would have populated @boot_command_line
-                */
-               if (uboot_tag == 1) {
-                       /* Ensure a whitespace between the 2 cmdlines */
-                       strlcat(boot_command_line, " ", COMMAND_LINE_SIZE);
-                       strlcat(boot_command_line, uboot_arg,
-                               COMMAND_LINE_SIZE);
-               }
+       /*
+        * NOTE: @boot_command_line is populated by setup_machine_fdt() so this
+        * append processing can only happen after.
+        */
+       if (append_cmdline) {
+               /* Ensure a whitespace between the 2 cmdlines */
+               strlcat(boot_command_line, " ", COMMAND_LINE_SIZE);
+               strlcat(boot_command_line, uboot_arg, COMMAND_LINE_SIZE);
        }
+}
+
+void __init setup_arch(char **cmdline_p)
+{
+       handle_uboot_args();
 
        /* Save unparsed command line copy for /proc/cmdline */
        *cmdline_p = boot_command_line;