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Commit edb64bca authored by Eugeniy Paltsev's avatar Eugeniy Paltsev Committed by Vineet Gupta
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ARC: u-boot args: check that magic number is correct 



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: default avatarEugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent fbe025c3

arch/arc/kernel/head.S

+1 −0
Original line number Diff line number Diff line
@@ -111,6 +111,7 @@ 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

arch/arc/kernel/setup.c

+8 −0
Original line number Diff line number Diff line
@@ -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;
@@ -504,6 +505,8 @@ 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)

{
@@ -518,6 +521,11 @@ 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);