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

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>
This commit is contained in:
Ard Biesheuvel 2023-01-09 18:47:59 +01:00 committed by Catalin Marinas
parent b7bfaa761d
commit 2198d07c50
3 changed files with 7 additions and 6 deletions
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7
arch/arm64/include/asm/scs.h
View File

@ -10,15 +10,16 @@
#ifdef CONFIG_SHADOW_CALL_STACK #ifdef CONFIG_SHADOW_CALL_STACK
scs_sp .req x18 scs_sp .req x18
.macro scs_load tsk .macro scs_load_current
ldr scs_sp, [\tsk, #TSK_TI_SCS_SP] get_current_task scs_sp
ldr scs_sp, [scs_sp, #TSK_TI_SCS_SP]
.endm .endm
.macro scs_save tsk .macro scs_save tsk
str scs_sp, [\tsk, #TSK_TI_SCS_SP] str scs_sp, [\tsk, #TSK_TI_SCS_SP]
.endm .endm
#else #else
.macro scs_load tsk .macro scs_load_current
.endm .endm
.macro scs_save tsk .macro scs_save tsk

4
arch/arm64/kernel/entry.S
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@ -275,7 +275,7 @@ alternative_if ARM64_HAS_ADDRESS_AUTH
alternative_else_nop_endif alternative_else_nop_endif
1: 1:
scs_load tsk scs_load_current
.else .else
add x21, sp, #PT_REGS_SIZE add x21, sp, #PT_REGS_SIZE
get_current_task tsk get_current_task tsk
@ -848,7 +848,7 @@ SYM_FUNC_START(cpu_switch_to)
msr sp_el0, x1 msr sp_el0, x1
ptrauth_keys_install_kernel x1, x8, x9, x10 ptrauth_keys_install_kernel x1, x8, x9, x10
scs_save x0 scs_save x0
scs_load x1 scs_load_current
ret ret
SYM_FUNC_END(cpu_switch_to) SYM_FUNC_END(cpu_switch_to)
NOKPROBE(cpu_switch_to) NOKPROBE(cpu_switch_to)

2
arch/arm64/kernel/head.S
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@ -404,7 +404,7 @@ SYM_FUNC_END(create_kernel_mapping)
stp xzr, xzr, [sp, #S_STACKFRAME] stp xzr, xzr, [sp, #S_STACKFRAME]
add x29, sp, #S_STACKFRAME add x29, sp, #S_STACKFRAME
scs_load \tsk scs_load_current
adr_l \tmp1, __per_cpu_offset adr_l \tmp1, __per_cpu_offset
ldr w\tmp2, [\tsk, #TSK_TI_CPU] ldr w\tmp2, [\tsk, #TSK_TI_CPU]