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arm64: Always load shadow stack pointer directly from the task struct

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commit 2198d07c509f1db4a1185d1f65aaada794c6ea59 upstream.

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>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ard Biesheuvel 2023-01-09 18:47:59 +01:00 committed by Greg Kroah-Hartman
parent a25a403e4b
commit 9134b5a464
3 changed files with 7 additions and 6 deletions
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7
arch/arm64/include/asm/scs.h
View File

@ -9,15 +9,16 @@
#ifdef CONFIG_SHADOW_CALL_STACK
scs_sp .req x18
.macro scs_load tsk, tmp
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, tmp
str scs_sp, [\tsk, #TSK_TI_SCS_SP]
.endm
#else
.macro scs_load tsk, tmp
.macro scs_load_current
.endm
.macro scs_save tsk, tmp

4
arch/arm64/kernel/entry.S
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@ -221,7 +221,7 @@ alternative_else_nop_endif
ptrauth_keys_install_kernel tsk, x20, x22, x23
scs_load tsk, x20
scs_load_current
.else
add x21, sp, #S_FRAME_SIZE
get_current_task tsk
@ -1025,7 +1025,7 @@ SYM_FUNC_START(cpu_switch_to)
msr sp_el0, x1
ptrauth_keys_install_kernel x1, x8, x9, x10
scs_save x0, x8
scs_load x1, x8
scs_load_current
ret
SYM_FUNC_END(cpu_switch_to)
NOKPROBE(cpu_switch_to)

2
arch/arm64/kernel/head.S
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@ -747,7 +747,7 @@ SYM_FUNC_START_LOCAL(__secondary_switched)
ldr x2, [x0, #CPU_BOOT_TASK]
cbz x2, __secondary_too_slow
msr sp_el0, x2
scs_load x2, x3
scs_load_current
mov x29, #0
mov x30, #0