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    Subject[PATCH v2 1/3] init/main.c: Give init_task a canary
    Date
    Tasks get their end of stack set to STACK_END_MAGIC with the
    aim to catch stack overruns. Currently this feature does not
    apply to init_task. This patch removes this restriction.

    Note that a similar patch was posted by Prarit Bhargava [1]
    some time ago but was never merged.

    [1]: http://marc.info/?l=linux-kernel&m=127144305403241&w=2

    Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
    ---
    arch/powerpc/mm/fault.c | 3 +--
    arch/x86/mm/fault.c | 3 +--
    include/linux/sched.h | 2 ++
    init/main.c | 1 +
    kernel/fork.c | 12 +++++++++---
    kernel/trace/trace_stack.c | 4 +---
    6 files changed, 15 insertions(+), 10 deletions(-)

    diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
    index 51ab9e7..35d0760c 100644
    --- a/arch/powerpc/mm/fault.c
    +++ b/arch/powerpc/mm/fault.c
    @@ -30,7 +30,6 @@
    #include <linux/kprobes.h>
    #include <linux/kdebug.h>
    #include <linux/perf_event.h>
    -#include <linux/magic.h>
    #include <linux/ratelimit.h>
    #include <linux/context_tracking.h>

    @@ -538,7 +537,7 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
    regs->nip);

    stackend = end_of_stack(current);
    - if (current != &init_task && *stackend != STACK_END_MAGIC)
    + if (*stackend != STACK_END_MAGIC)
    printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");

    die("Kernel access of bad area", regs, sig);
    diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
    index a241946..bc23a70 100644
    --- a/arch/x86/mm/fault.c
    +++ b/arch/x86/mm/fault.c
    @@ -3,7 +3,6 @@
    * Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs.
    * Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar
    */
    -#include <linux/magic.h> /* STACK_END_MAGIC */
    #include <linux/sched.h> /* test_thread_flag(), ... */
    #include <linux/kdebug.h> /* oops_begin/end, ... */
    #include <linux/module.h> /* search_exception_table */
    @@ -710,7 +709,7 @@ no_context(struct pt_regs *regs, unsigned long error_code,
    show_fault_oops(regs, error_code, address);

    stackend = end_of_stack(tsk);
    - if (tsk != &init_task && *stackend != STACK_END_MAGIC)
    + if (*stackend != STACK_END_MAGIC)
    printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");

    tsk->thread.cr2 = address;
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 5c2c885..4dee9d7 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -57,6 +57,7 @@ struct sched_param {
    #include <linux/llist.h>
    #include <linux/uidgid.h>
    #include <linux/gfp.h>
    +#include <linux/magic.h>

    #include <asm/processor.h>

    @@ -2636,6 +2637,7 @@ static inline unsigned long stack_not_used(struct task_struct *p)
    return (unsigned long)n - (unsigned long)end_of_stack(p);
    }
    #endif
    +extern void task_stack_end_magic(struct task_struct *tsk);

    /* set thread flags in other task's structures
    * - see asm/thread_info.h for TIF_xxxx flags available
    diff --git a/init/main.c b/init/main.c
    index bb1aed9..bcdabf3a 100644
    --- a/init/main.c
    +++ b/init/main.c
    @@ -508,6 +508,7 @@ asmlinkage __visible void __init start_kernel(void)
    * lockdep hash:
    */
    lockdep_init();
    + task_stack_end_magic(&init_task);
    smp_setup_processor_id();
    debug_objects_early_init();

    diff --git a/kernel/fork.c b/kernel/fork.c
    index 0cf9cdb..67cb1e3 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -294,11 +294,18 @@ int __weak arch_dup_task_struct(struct task_struct *dst,
    return 0;
    }

    +void task_stack_end_magic(struct task_struct *tsk)
    +{
    + unsigned long *stackend;
    +
    + stackend = end_of_stack(tsk);
    + *stackend = STACK_END_MAGIC; /* for overflow detection */
    +}
    +
    static struct task_struct *dup_task_struct(struct task_struct *orig)
    {
    struct task_struct *tsk;
    struct thread_info *ti;
    - unsigned long *stackend;
    int node = tsk_fork_get_node(orig);
    int err;

    @@ -328,8 +335,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
    setup_thread_stack(tsk, orig);
    clear_user_return_notifier(tsk);
    clear_tsk_need_resched(tsk);
    - stackend = end_of_stack(tsk);
    - *stackend = STACK_END_MAGIC; /* for overflow detection */
    + task_stack_end_magic(tsk);

    #ifdef CONFIG_CC_STACKPROTECTOR
    tsk->stack_canary = get_random_int();
    diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
    index 8a4e5cb..1636e41 100644
    --- a/kernel/trace/trace_stack.c
    +++ b/kernel/trace/trace_stack.c
    @@ -13,7 +13,6 @@
    #include <linux/sysctl.h>
    #include <linux/init.h>
    #include <linux/fs.h>
    -#include <linux/magic.h>

    #include <asm/setup.h>

    @@ -171,8 +170,7 @@ check_stack(unsigned long ip, unsigned long *stack)
    i++;
    }

    - if ((current != &init_task &&
    - *(end_of_stack(current)) != STACK_END_MAGIC)) {
    + if (*end_of_stack(current) != STACK_END_MAGIC) {
    print_max_stack();
    BUG();
    }
    --
    1.9.3


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