From: Ard Biesheuvel <ardb@kernel.org>
Date: Mon, 9 Jan 2023 18:48:00 +0100
Subject: arm64: Stash shadow stack pointer in the task struct on interrupt
Git-commit: 59b37fe52f49955791a460752c37145f1afdcad1
Patch-mainline: v6.3-rc1
References: git-fixes
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: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20230109174800.3286265-3-ardb@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Ivan T. Ivanov <iivanov@suse.de>
---
arch/arm64/kernel/entry.S | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -907,19 +907,19 @@ 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
/*
@@ -928,9 +928,7 @@ 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)