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Subject[PATCH 1/2] ARC: U-boot: check arguments paranoidly
Date
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.
* check that magic number is correct.
* 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.

NOTE:
We can safely check U-boot magic value (0x0) in linux passed via
r1 register as U-boot pass it from the beginning.

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

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
---
arch/arc/kernel/head.S | 5 +--
arch/arc/kernel/setup.c | 92 +++++++++++++++++++++++++++++++++++--------------
2 files changed, 69 insertions(+), 28 deletions(-)

diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
index 8b90d25a15cc..fccea361e896 100644
--- a/arch/arc/kernel/head.S
+++ b/arch/arc/kernel/head.S
@@ -93,10 +93,11 @@ 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 r1, [@uboot_magic]
st r2, [@uboot_arg]
#endif

diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
index feb90093e6b1..84d394a37e79 100644
--- a/arch/arc/kernel/setup.c
+++ b/arch/arc/kernel/setup.c
@@ -36,7 +36,8 @@ unsigned int intr_to_DE_cnt;

/* Part of U-boot ABI: see head.S */
int __initdata uboot_tag;
-char __initdata *uboot_arg;
+int __initdata uboot_magic;
+unsigned int __initdata uboot_arg;

const struct machine_desc *machine_desc;

@@ -462,43 +463,82 @@ void setup_processor(void)
arc_chk_core_config();
}

-static inline int is_kernel(unsigned long addr)
+static inline bool uboot_arg_invalid(unsigned int 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 int)_stext && addr <= (unsigned int)_end;
}

-void __init setup_arch(char **cmdline_p)
+#define IGNORE_ARGS "Ignore U-boot args: "
+
+/* uboot_{tag, magic} 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
+/* We always pass 0 as magic from U-boot */
+#define UBOOT_MAGIC_VAL 0
+
+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_magic != UBOOT_MAGIC_VAL) {
+ pr_warn(IGNORE_ARGS "non zero uboot magic\n");
+ goto ignore_uboot_args;
+ }
+
+ if (uboot_tag != UBOOT_TAG_NONE && uboot_arg_invalid(uboot_arg)) {
+ pr_warn(IGNORE_ARGS "invalid uboot arg: '%08x'\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);
+
+ /* external Device Tree blob is invalid - use embedded one */
+ use_embedded_dtb = !machine_desc;
+ }
+
+ if (uboot_tag == UBOOT_TAG_CMDLINE)
+ append_cmdline = true;

- /* See if u-boot passed an external Device Tree blob */
- machine_desc = setup_machine_fdt(uboot_arg); /* uboot_tag == 2 */
- if (!machine_desc)
+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);
- }
+ if (append_cmdline) {
+ /* Ensure a whitespace between the 2 cmdlines */
+ strlcat(boot_command_line, " ", COMMAND_LINE_SIZE);
+ strlcat(boot_command_line, (char *)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;
--
2.14.5
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