Patch "ARC: u-boot args: check that magic number is correct" has been added to the 5.0-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ARC: u-boot args: check that magic number is correct

to the 5.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arc-u-boot-args-check-that-magic-number-is-correct.patch
and it can be found in the queue-5.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ffcca3375f453c6d1ebcdc7ab595eeb7356b1526
Author: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
Date:   Mon Feb 25 20:16:01 2019 +0300

    ARC: u-boot args: check that magic number is correct
    
    [ Upstream commit edb64bca50cd736c6894cc6081d5263c007ce005 ]
    
    In case of devboards we really often disable bootloader and load
    Linux image in memory via JTAG. Even if kernel tries to verify
    uboot_tag and uboot_arg there is sill a chance that we treat some
    garbage in registers as valid u-boot arguments in JTAG case.
    E.g. it is enough to have '1' in r0 to treat any value in r2 as
    a boot command line.
    
    So check that magic number passed from u-boot is correct and drop
    u-boot arguments otherwise. That helps to reduce the possibility
    of using garbage as u-boot arguments in JTAG case.
    
    We can safely check U-boot magic value (0x0) in linux passed via
    r1 register as U-boot pass it from the beginning. So there is no
    backward-compatibility issues.
    
    Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
    Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
index 30e090625916..a72bbda2f7aa 100644
--- a/arch/arc/kernel/head.S
+++ b/arch/arc/kernel/head.S
@@ -106,6 +106,7 @@ ENTRY(stext)
 	;    r2 = pointer to uboot provided cmdline or external DTB in mem
 	; These are handled later in handle_uboot_args()
 	st	r0, [@uboot_tag]
+	st      r1, [@uboot_magic]
 	st	r2, [@uboot_arg]
 
 	; setup "current" tsk and optionally cache it in dedicated r25
diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
index 7b2340996cf8..7b3a7b3b380c 100644
--- a/arch/arc/kernel/setup.c
+++ b/arch/arc/kernel/setup.c
@@ -36,6 +36,7 @@ unsigned int intr_to_DE_cnt;
 
 /* Part of U-boot ABI: see head.S */
 int __initdata uboot_tag;
+int __initdata uboot_magic;
 char __initdata *uboot_arg;
 
 const struct machine_desc *machine_desc;
@@ -497,6 +498,8 @@ static inline bool uboot_arg_invalid(unsigned long addr)
 #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_VALUE	0
 
 void __init handle_uboot_args(void)
 {
@@ -511,6 +514,11 @@ void __init handle_uboot_args(void)
 		goto ignore_uboot_args;
 	}
 
+	if (uboot_magic != UBOOT_MAGIC_VALUE) {
+		pr_warn(IGNORE_ARGS "non zero uboot magic\n");
+		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);