From: Ard Biesheuvel <ardb@kernel.org>
Date: Mon, 9 Jan 2023 18:47:59 +0100
Subject: arm64: Always load shadow stack pointer directly from the task struct
Git-commit: 2198d07c509f1db4a1185d1f65aaada794c6ea59
Patch-mainline: v6.3-rc1
References: git-fixes
All occurrences of the scs_load macro load the value of the shadow call
stack pointer from the task which is current at that point. So instead
of taking a task struct register argument in the scs_load macro to
specify the task struct to load from, let's always reference the current
task directly. This should make it much harder to exploit any
instruction sequences reloading the shadow call stack pointer register
from memory.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230109174800.3286265-2-ardb@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Ivan T. Ivanov <iivanov@suse.de>
---
arch/arm64/include/asm/scs.h | 7 ++++---
arch/arm64/kernel/entry.S | 4 ++--
arch/arm64/kernel/head.S | 2 +-
3 files changed, 7 insertions(+), 6 deletions(-)
--- a/arch/arm64/include/asm/scs.h
+++ b/arch/arm64/include/asm/scs.h
@@ -9,15 +9,16 @@
#ifdef CONFIG_SHADOW_CALL_STACK
scs_sp .req x18
- .macro scs_load tsk
- ldr scs_sp, [\tsk, #TSK_TI_SCS_SP]
+ .macro scs_load_current
+ get_current_task scs_sp
+ ldr scs_sp, [scs_sp, #TSK_TI_SCS_SP]
.endm
.macro scs_save tsk
str scs_sp, [\tsk, #TSK_TI_SCS_SP]
.endm
#else
- .macro scs_load tsk
+ .macro scs_load_current
.endm
.macro scs_save tsk
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -267,7 +267,7 @@ alternative_else_nop_endif
mte_set_kernel_gcr x22, x23
- scs_load tsk
+ scs_load_current
.else
add x21, sp, #PT_REGS_SIZE
get_current_task tsk
@@ -881,7 +881,7 @@ SYM_FUNC_START(cpu_switch_to)
msr sp_el0, x1
ptrauth_keys_install_kernel x1, x8, x9, x10
scs_save x0
- scs_load x1
+ scs_load_current
ret
SYM_FUNC_END(cpu_switch_to)
NOKPROBE(cpu_switch_to)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -409,7 +409,7 @@ SYM_FUNC_END(__create_page_tables)
stp xzr, xzr, [sp, #S_STACKFRAME]
add x29, sp, #S_STACKFRAME
- scs_load \tsk
+ scs_load_current
adr_l \tmp1, __per_cpu_offset
ldr w\tmp2, [\tsk, #TSK_CPU]