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FROMLIST: arm64: implement Shadow Call Stack

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This change implements shadow stack switching, initial SCS set-up,
and interrupt shadow stacks for arm64.

Bug: 145210207
Change-Id: I3d5b9ec374418b110d1f351e1abd41610cfee597
(am from https://lore.kernel.org/patchwork/patch/1149062/)
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
This commit is contained in:
Sami Tolvanen 2018-05-02 11:05:22 -07:00 committed by Alistair Delva
parent fb3573ae71
commit 332eaac720
12 changed files with 140 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/arm64/Kconfig
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@ -59,6 +59,7 @@ config ARM64
select ARCH_SUPPORTS_MEMORY_FAILURE
select ARCH_SUPPORTS_LTO_CLANG
select ARCH_SUPPORTS_THINLTO
select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_INT128 if GCC_VERSION >= 50000 || CC_IS_CLANG
select ARCH_SUPPORTS_NUMA_BALANCING
@ -824,6 +825,11 @@ config ARCH_WANT_HUGE_PMD_SHARE
config ARCH_HAS_CACHE_LINE_SIZE
def_bool y
# Supported by clang >= 7.0
config CC_HAVE_SHADOW_CALL_STACK
def_bool $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18)
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
---help---

37
arch/arm64/include/asm/scs.h Normal file
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@ -0,0 +1,37 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_SCS_H
#define _ASM_SCS_H
#ifndef __ASSEMBLY__
#include <linux/scs.h>
#ifdef CONFIG_SHADOW_CALL_STACK
extern void scs_init_irq(void);
static __always_inline void scs_save(struct task_struct *tsk)
{
void *s;
asm volatile("mov %0, x18" : "=r" (s));
task_set_scs(tsk, s);
}
static inline void scs_overflow_check(struct task_struct *tsk)
{
if (unlikely(scs_corrupted(tsk)))
panic("corrupted shadow stack detected inside scheduler\n");
}
#else /* CONFIG_SHADOW_CALL_STACK */
static inline void scs_init_irq(void) {}
static inline void scs_save(struct task_struct *tsk) {}
static inline void scs_overflow_check(struct task_struct *tsk) {}
#endif /* CONFIG_SHADOW_CALL_STACK */
#endif /* __ASSEMBLY __ */
#endif /* _ASM_SCS_H */

4
arch/arm64/include/asm/stacktrace.h
View File

@ -54,6 +54,10 @@ extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);
DECLARE_PER_CPU(unsigned long *, irq_stack_ptr);
#ifdef CONFIG_SHADOW_CALL_STACK
DECLARE_PER_CPU(unsigned long *, irq_shadow_call_stack_ptr);
#endif
static inline bool on_irq_stack(unsigned long sp,
struct stack_info *info)
{

3
arch/arm64/include/asm/thread_info.h
View File

@ -43,6 +43,9 @@ struct thread_info {
u64 ttbr0; /* saved TTBR0_EL1 */
#endif
int preempt_count; /* 0 => preemptable, <0 => bug */
#ifdef CONFIG_SHADOW_CALL_STACK
void *shadow_call_stack;
#endif
};
#define thread_saved_pc(tsk) \

1
arch/arm64/kernel/Makefile
View File

@ -57,6 +57,7 @@ arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
arm64-obj-$(CONFIG_CRASH_CORE) += crash_core.o
arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o
arm64-obj-$(CONFIG_ARM64_SSBD) += ssbd.o
arm64-obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o
obj-y += $(arm64-obj-y) vdso/ probes/
obj-m += $(arm64-obj-m)

3
arch/arm64/kernel/asm-offsets.c
View File

@ -44,6 +44,9 @@ int main(void)
DEFINE(TSK_TI_ADDR_LIMIT, offsetof(struct task_struct, thread_info.addr_limit));
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
DEFINE(TSK_TI_TTBR0, offsetof(struct task_struct, thread_info.ttbr0));
#endif
#ifdef CONFIG_SHADOW_CALL_STACK
DEFINE(TSK_TI_SCS, offsetof(struct task_struct, thread_info.shadow_call_stack));
#endif
DEFINE(TSK_STACK, offsetof(struct task_struct, stack));
BLANK();

31
arch/arm64/kernel/entry.S
View File

@ -183,6 +183,10 @@ alternative_cb_end
apply_ssbd 1, x22, x23
#ifdef CONFIG_SHADOW_CALL_STACK
ldr x18, [tsk, #TSK_TI_SCS] // Restore shadow call stack
str xzr, [tsk, #TSK_TI_SCS] // Limit visibility of saved SCS
#endif
.else
add x21, sp, #S_FRAME_SIZE
get_thread_info tsk
@ -274,6 +278,12 @@ alternative_else_nop_endif
ct_user_enter
.endif
#ifdef CONFIG_SHADOW_CALL_STACK
.if \el == 0
str x18, [tsk, #TSK_TI_SCS] // Save shadow call stack
.endif
#endif
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
/*
* Restore access to TTBR0_EL1. If returning to EL0, no need for SPSR
@ -367,6 +377,9 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
.macro irq_stack_entry
mov x19, sp // preserve the original sp
#ifdef CONFIG_SHADOW_CALL_STACK
mov x20, x18 // preserve the original shadow stack
#endif
/*
* Compare sp with the base of the task stack.
@ -384,15 +397,24 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
/* switch to the irq stack */
mov sp, x26
#ifdef CONFIG_SHADOW_CALL_STACK
/* also switch to the irq shadow stack */
ldr_this_cpu x18, irq_shadow_call_stack_ptr, x26
#endif
9998:
.endm
/*
* x19 should be preserved between irq_stack_entry and
* irq_stack_exit.
* The callee-saved regs (x19-x29) should be preserved between
* irq_stack_entry and irq_stack_exit.
*/
.macro irq_stack_exit
mov sp, x19
#ifdef CONFIG_SHADOW_CALL_STACK
mov x18, x20
#endif
.endm
/*
@ -1060,6 +1082,11 @@ ENTRY(cpu_switch_to)
ldr lr, [x8]
mov sp, x9
msr sp_el0, x1
#ifdef CONFIG_SHADOW_CALL_STACK
str x18, [x0, #TSK_TI_SCS]
ldr x18, [x1, #TSK_TI_SCS]
str xzr, [x1, #TSK_TI_SCS] // limit visibility of saved SCS
#endif
ret
ENDPROC(cpu_switch_to)
NOKPROBE(cpu_switch_to)

9
arch/arm64/kernel/head.S
View File

@ -37,6 +37,7 @@
#include <asm/pgtable-hwdef.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include <asm/scs.h>
#include <asm/smp.h>
#include <asm/sysreg.h>
#include <asm/thread_info.h>
@ -419,6 +420,10 @@ __primary_switched:
stp xzr, x30, [sp, #-16]!
mov x29, sp
#ifdef CONFIG_SHADOW_CALL_STACK
adr_l x18, init_shadow_call_stack // Set shadow call stack
#endif
str_l x21, __fdt_pointer, x5 // Save FDT pointer
ldr_l x4, kimage_vaddr // Save the offset between
@ -721,6 +726,10 @@ __secondary_switched:
mov sp, x1
ldr x2, [x0, #CPU_BOOT_TASK]
msr sp_el0, x2
#ifdef CONFIG_SHADOW_CALL_STACK
ldr x18, [x2, #TSK_TI_SCS] // set shadow call stack
str xzr, [x2, #TSK_TI_SCS] // limit visibility of saved SCS
#endif
mov x29, #0
mov x30, #0
b secondary_start_kernel

2
arch/arm64/kernel/irq.c
View File

@ -30,6 +30,7 @@
#include <linux/seq_file.h>
#include <linux/vmalloc.h>
#include <asm/vmap_stack.h>
#include <asm/scs.h>
unsigned long irq_err_count;
@ -72,6 +73,7 @@ static void init_irq_stacks(void)
void __init init_IRQ(void)
{
init_irq_stacks();
scs_init_irq();
irqchip_init();
if (!handle_arch_irq)
panic("No interrupt controller found.");

2
arch/arm64/kernel/process.c
View File

@ -59,6 +59,7 @@
#include <asm/fpsimd.h>
#include <asm/mmu_context.h>
#include <asm/processor.h>
#include <asm/scs.h>
#include <asm/stacktrace.h>
#ifdef CONFIG_STACKPROTECTOR
@ -463,6 +464,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
entry_task_switch(next);
uao_thread_switch(next);
ssbs_thread_switch(next);
scs_overflow_check(next);
/*
* Complete any pending TLB or cache maintenance on this CPU in case

40
arch/arm64/kernel/scs.c Normal file
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@ -0,0 +1,40 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Shadow Call Stack support.
*
* Copyright (C) 2019 Google LLC
*/
#include <linux/percpu.h>
#include <linux/vmalloc.h>
#include <asm/pgtable.h>
#include <asm/scs.h>
DEFINE_PER_CPU(unsigned long *, irq_shadow_call_stack_ptr);
#ifndef CONFIG_SHADOW_CALL_STACK_VMAP
DEFINE_PER_CPU(unsigned long [SCS_SIZE/sizeof(long)], irq_shadow_call_stack)
__aligned(SCS_SIZE);
#endif
void scs_init_irq(void)
{
int cpu;
for_each_possible_cpu(cpu) {
#ifdef CONFIG_SHADOW_CALL_STACK_VMAP
unsigned long *p;
p = __vmalloc_node_range(PAGE_SIZE, SCS_SIZE,
VMALLOC_START, VMALLOC_END,
GFP_SCS, PAGE_KERNEL,
0, cpu_to_node(cpu),
__builtin_return_address(0));
per_cpu(irq_shadow_call_stack_ptr, cpu) = p;
#else
per_cpu(irq_shadow_call_stack_ptr, cpu) =
per_cpu(irq_shadow_call_stack, cpu);
#endif /* CONFIG_SHADOW_CALL_STACK_VMAP */
}
}

4
arch/arm64/kernel/smp.c
View File

@ -54,6 +54,7 @@
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/processor.h>
#include <asm/scs.h>
#include <asm/smp_plat.h>
#include <asm/sections.h>
#include <asm/tlbflush.h>
@ -343,6 +344,9 @@ void cpu_die(void)
{
unsigned int cpu = smp_processor_id();
/* Save the shadow stack pointer before exiting the idle task */
scs_save(current);
idle_task_exit();
local_daif_mask();