Commit 59b37fe5 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Catalin Marinas
Browse files

arm64: Stash shadow stack pointer in the task struct on interrupt 



Instead of reloading the shadow call stack pointer from the ordinary
stack, which may be vulnerable to the kind of gadget based attacks
shadow call stacks were designed to prevent, let's store a task's shadow
call stack pointer in the task struct when switching to the shadow IRQ
stack.

Given that currently, the task_struct::scs_sp field is only used to
preserve the shadow call stack pointer while a task is scheduled out or
running in user space, reusing this field to preserve and restore it
while running off the IRQ stack must be safe, as those occurrences are
guaranteed to never overlap. (The stack switching logic only switches
stacks when running from the task stack, and so the value being saved
here always corresponds to the task mode shadow stack)

While at it, fold a mov/add/mov sequence into a single add.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20230109174800.3286265-3-ardb@kernel.org


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 2198d07c

arch/arm64/kernel/entry.S

+5 −7
Original line number Diff line number Diff line
@@ -876,19 +876,19 @@ NOKPROBE(ret_from_fork) 
 */

SYM_FUNC_START(call_on_irq_stack)

#ifdef CONFIG_SHADOW_CALL_STACK

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

	get_current_task x16

	scs_save x16

	ldr_this_cpu scs_sp, irq_shadow_call_stack_ptr, x17

#endif



	/* Create a frame record to save our LR and SP (implicit in FP) */

	stp	x29, x30, [sp, #-16]!

	mov	x29, sp



	ldr_this_cpu x16, irq_stack_ptr, x17

	mov	x15, #IRQ_STACK_SIZE

	add	x16, x16, x15



	/* Move to the new stack and call the function there */

	mov	sp, x16

	add	sp, x16, #IRQ_STACK_SIZE

	blr	x1



	/*
@@ -897,9 +897,7 @@ SYM_FUNC_START(call_on_irq_stack) 
	 */

	mov	sp, x29

	ldp	x29, x30, [sp], #16

#ifdef CONFIG_SHADOW_CALL_STACK

	ldp	scs_sp, xzr, [sp], #16

#endif

	scs_load_current

	ret

SYM_FUNC_END(call_on_irq_stack)

NOKPROBE(call_on_irq_stack)