Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit da9c177d authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Will Deacon
Browse files

arm64: enforce x1|x2|x3 == 0 upon kernel entry as per boot protocol 



According to the arm64 boot protocol, registers x1 to x3 should be
zero upon kernel entry, and non-zero values are reserved for future
use. This future use is going to be problematic if we never enforce
the current rules, so start enforcing them now, by emitting a warning
if non-zero values are detected.

Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 6f4d57fa

arch/arm64/kernel/head.S

+18 −1
Original line number Diff line number Diff line
@@ -233,7 +233,7 @@ section_table: 
#endif



ENTRY(stext)

	mov	x21, x0				// x21=FDT

	bl	preserve_boot_args

	bl	el2_setup			// Drop to EL1, w20=cpu_boot_mode

	adrp	x24, __PHYS_OFFSET

	bl	set_cpu_boot_mode_flag
@@ -252,6 +252,23 @@ ENTRY(stext) 
	b	__cpu_setup			// initialise processor

ENDPROC(stext)



/*

 * Preserve the arguments passed by the bootloader in x0 .. x3

 */

preserve_boot_args:

	mov	x21, x0				// x21=FDT



	adr_l	x0, boot_args			// record the contents of

	stp	x21, x1, [x0]			// x0 .. x3 at kernel entry

	stp	x2, x3, [x0, #16]



	dmb	sy				// needed before dc ivac with

						// MMU off



	add	x1, x0, #0x20			// 4 x 8 bytes

	b	__inval_cache_range		// tail call

ENDPROC(preserve_boot_args)



/*

 * Determine validity of the x21 FDT pointer.

 * The dtb must be 8-byte aligned and live in the first 512M of memory.

arch/arm64/kernel/setup.c

+11 −0
Original line number Diff line number Diff line
@@ -115,6 +115,11 @@ void __init early_print(const char *str, ...) 
	printk("%s", buf);

}



/*

 * The recorded values of x0 .. x3 upon kernel entry.

 */

u64 __cacheline_aligned boot_args[4];



void __init smp_setup_processor_id(void)

{

	u64 mpidr = read_cpuid_mpidr() & MPIDR_HWID_BITMASK;
@@ -412,6 +417,12 @@ void __init setup_arch(char **cmdline_p) 
	conswitchp = &dummy_con;

#endif

#endif

	if (boot_args[1] || boot_args[2] || boot_args[3]) {

		pr_err("WARNING: x1-x3 nonzero in violation of boot protocol:\n"

			"\tx1: %016llx\n\tx2: %016llx\n\tx3: %016llx\n"

			"This indicates a broken bootloader or old kernel\n",

			boot_args[1], boot_args[2], boot_args[3]);

	}

}



static int __init arm64_device_init(void)