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Commit 60699ba1 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Will Deacon
Browse files

arm64: head.S: use ordinary stack frame for __primary_switched() 



Instead of stashing the value of the link register in x28 before setting
up the stack and calling into C code, create an ordinary PCS compatible
stack frame so that we can push the return address onto the stack.

Since exception handlers require a stack as well, assign the stack pointer
register before installing the vector table.

Note that this accounts for the difference between THREAD_START_SP and
THREAD_SIZE, given that the stack pointer is always decremented before
calling into any C code.

Reviewed-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 b929fe32

arch/arm64/kernel/head.S

+9 −9
Original line number Diff line number Diff line
@@ -415,13 +415,18 @@ ENDPROC(__create_page_tables) 
 *

 *   x0 = __PHYS_OFFSET

 */

	.set	initial_sp, init_thread_union + THREAD_START_SP

__primary_switched:

	mov	x28, lr				// preserve LR

	adrp	x4, init_thread_union

	add	sp, x4, #THREAD_SIZE

	msr	sp_el0, x4			// Save thread_info



	adr_l	x8, vectors			// load VBAR_EL1 with virtual

	msr	vbar_el1, x8			// vector table address

	isb



	stp	xzr, x30, [sp, #-16]!

	mov	x29, sp



	str_l	x21, __fdt_pointer, x5		// Save FDT pointer



	ldr_l	x4, kimage_vaddr		// Save the offset between
@@ -436,11 +441,6 @@ __primary_switched: 
	bl	__pi_memset

	dsb	ishst				// Make zero page visible to PTW



	adr_l	sp, initial_sp, x4

	mov	x4, sp

	and	x4, x4, #~(THREAD_SIZE - 1)

	msr	sp_el0, x4			// Save thread_info

	mov	x29, #0

#ifdef CONFIG_KASAN

	bl	kasan_early_init

#endif
@@ -452,8 +452,8 @@ __primary_switched: 
	bl	kaslr_early_init		// parse FDT for KASLR options

	cbz	x0, 0f				// KASLR disabled? just proceed

	orr	x23, x23, x0			// record KASLR offset

	ret	x28				// we must enable KASLR, return

						// to __primary_switch()

	ldp	x29, x30, [sp], #16		// we must enable KASLR, return

	ret					// to __primary_switch()

0:

#endif

	b	start_kernel