ARC: U-boot: check arguments paranoidly [Linux 5.0]

ARC: U-boot: check arguments paranoidly [Linux 5.0]

This Linux kernel change "ARC: U-boot: check arguments paranoidly" is included in the Linux 5.0 release. This change is authored by Eugeniy Paltsev <Eugeniy.Paltsev [at] synopsys.com> on Thu Feb 14 18:07:44 2019 +0300. The commit for this change in Linux stable tree is a66f2e5 (patch).

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: [email protected]
Tested-by: Corentin LABBE <[email protected]>
Signed-off-by: Eugeniy Paltsev <[email protected]>
Signed-off-by: Vineet Gupta <[email protected]>

There are 91 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 arch/arc/kernel/head.S  |  4 +--
 arch/arc/kernel/setup.c | 87 +++++++++++++++++++++++++++++++++++--------------
 2 files changed, 64 insertions(+), 27 deletions(-)

diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
index 26e33a8..1f945d0 100644
--- 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
--- 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;

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