lkml.org 
[lkml]   [2020]   [Feb]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    Subject[PATCH v8 10/12] arm64: implement Shadow Call Stack
    From
    This change implements shadow stack switching, initial SCS set-up,
    and interrupt shadow stacks for arm64.

    Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    ---
    arch/arm64/Kconfig | 5 ++++
    arch/arm64/include/asm/scs.h | 37 +++++++++++++++++++++++++
    arch/arm64/include/asm/thread_info.h | 3 +++
    arch/arm64/kernel/Makefile | 1 +
    arch/arm64/kernel/asm-offsets.c | 3 +++
    arch/arm64/kernel/entry.S | 32 ++++++++++++++++++++--
    arch/arm64/kernel/head.S | 9 +++++++
    arch/arm64/kernel/irq.c | 2 ++
    arch/arm64/kernel/process.c | 2 ++
    arch/arm64/kernel/scs.c | 40 ++++++++++++++++++++++++++++
    arch/arm64/kernel/smp.c | 4 +++
    11 files changed, 136 insertions(+), 2 deletions(-)
    create mode 100644 arch/arm64/include/asm/scs.h
    create mode 100644 arch/arm64/kernel/scs.c

    diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    index 0b30e884e088..eae76686be77 100644
    --- a/arch/arm64/Kconfig
    +++ b/arch/arm64/Kconfig
    @@ -65,6 +65,7 @@ config ARM64
    select ARCH_USE_QUEUED_RWLOCKS
    select ARCH_USE_QUEUED_SPINLOCKS
    select ARCH_SUPPORTS_MEMORY_FAILURE
    + select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK
    select ARCH_SUPPORTS_ATOMIC_RMW
    select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && (GCC_VERSION >= 50000 || CC_IS_CLANG)
    select ARCH_SUPPORTS_NUMA_BALANCING
    @@ -1022,6 +1023,10 @@ config ARCH_HAS_CACHE_LINE_SIZE
    config ARCH_ENABLE_SPLIT_PMD_PTLOCK
    def_bool y if PGTABLE_LEVELS > 2

    +# 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---
    diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h
    new file mode 100644
    index 000000000000..c50d2b0c6c5f
    --- /dev/null
    +++ b/arch/arm64/include/asm/scs.h
    @@ -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 */
    diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
    index f0cec4160136..8c73764b9ed2 100644
    --- a/arch/arm64/include/asm/thread_info.h
    +++ b/arch/arm64/include/asm/thread_info.h
    @@ -41,6 +41,9 @@ struct thread_info {
    #endif
    } preempt;
    };
    +#ifdef CONFIG_SHADOW_CALL_STACK
    + void *shadow_call_stack;
    +#endif
    };

    #define thread_saved_pc(tsk) \
    diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
    index fc6488660f64..08fafc4da2cf 100644
    --- a/arch/arm64/kernel/Makefile
    +++ b/arch/arm64/kernel/Makefile
    @@ -63,6 +63,7 @@ obj-$(CONFIG_CRASH_CORE) += crash_core.o
    obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o
    obj-$(CONFIG_ARM64_SSBD) += ssbd.o
    obj-$(CONFIG_ARM64_PTR_AUTH) += pointer_auth.o
    +obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o

    obj-y += vdso/ probes/
    obj-$(CONFIG_COMPAT_VDSO) += vdso32/
    diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
    index a5bdce8af65b..d485dc5cd196 100644
    --- a/arch/arm64/kernel/asm-offsets.c
    +++ b/arch/arm64/kernel/asm-offsets.c
    @@ -33,6 +33,9 @@ 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));
    #ifdef CONFIG_STACKPROTECTOR
    diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
    index 9461d812ae27..4b18c3bbdea5 100644
    --- a/arch/arm64/kernel/entry.S
    +++ b/arch/arm64/kernel/entry.S
    @@ -177,6 +177,10 @@ 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_current_task tsk
    @@ -278,6 +282,12 @@ 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
    @@ -383,6 +393,9 @@ 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 x24, x18 // preserve the original shadow stack
    +#endif

    /*
    * Compare sp with the base of the task stack.
    @@ -400,15 +413,25 @@ 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, but note that kernel_entry
    + * uses x20-x23 to store data for later use.
    */
    .macro irq_stack_exit
    mov sp, x19
    +#ifdef CONFIG_SHADOW_CALL_STACK
    + mov x18, x24
    +#endif
    .endm

    /* GPRs used by entry code */
    @@ -895,6 +918,11 @@ 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)
    diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
    index 989b1944cb71..ca561de903d4 100644
    --- a/arch/arm64/kernel/head.S
    +++ b/arch/arm64/kernel/head.S
    @@ -27,6 +27,7 @@
    #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>
    @@ -424,6 +425,10 @@ __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
    @@ -731,6 +736,10 @@ __secondary_switched:
    ldr x2, [x0, #CPU_BOOT_TASK]
    cbz x2, __secondary_too_slow
    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
    diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
    index 04a327ccf84d..fe0ca522ff60 100644
    --- a/arch/arm64/kernel/irq.c
    +++ b/arch/arm64/kernel/irq.c
    @@ -21,6 +21,7 @@
    #include <linux/vmalloc.h>
    #include <asm/daifflags.h>
    #include <asm/vmap_stack.h>
    +#include <asm/scs.h>

    unsigned long irq_err_count;

    @@ -63,6 +64,7 @@ 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.");
    diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
    index 00626057a384..9151616c354c 100644
    --- a/arch/arm64/kernel/process.c
    +++ b/arch/arm64/kernel/process.c
    @@ -52,6 +52,7 @@
    #include <asm/mmu_context.h>
    #include <asm/processor.h>
    #include <asm/pointer_auth.h>
    +#include <asm/scs.h>
    #include <asm/stacktrace.h>

    #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
    @@ -514,6 +515,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
    uao_thread_switch(next);
    ptrauth_thread_switch(next);
    ssbs_thread_switch(next);
    + scs_overflow_check(next);

    /*
    * Complete any pending TLB or cache maintenance on this CPU in case
    diff --git a/arch/arm64/kernel/scs.c b/arch/arm64/kernel/scs.c
    new file mode 100644
    index 000000000000..eaadf5430baa
    --- /dev/null
    +++ b/arch/arm64/kernel/scs.c
    @@ -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 */
    + }
    +}
    diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
    index d4ed9a19d8fe..f2cb344f998c 100644
    --- a/arch/arm64/kernel/smp.c
    +++ b/arch/arm64/kernel/smp.c
    @@ -46,6 +46,7 @@
    #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>
    @@ -358,6 +359,9 @@ 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();
    --
    2.25.0.265.gbab2e86ba0-goog
    \
     
     \ /
      Last update: 2020-02-19 01:09    [W:3.642 / U:0.168 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site