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    Subject[PATCH 3.16 266/410] arm64: traps: Don't print stack or raw PC/LR values in backtraces
    3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Will Deacon <will.deacon@arm.com>

    commit a25ffd3a6302a67814280274d8f1aa4ae2ea4b59 upstream.

    Printing raw pointer values in backtraces has potential security
    implications and are of questionable value anyway.

    This patch follows x86's lead and removes the "Exception stack:" dump
    from kernel backtraces, as well as converting PC/LR values to symbols
    such as "sysrq_handle_crash+0x20/0x30".

    Tested-by: Laura Abbott <labbott@redhat.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    [bwh: Backported to 3.16:
    - Deleted code in dump_mem() and dump_backtrace_entry() is a bit different
    - Leave dump_backtrace() unchanged, since it doesn't use dump_mem()]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/arch/arm64/kernel/process.c
    +++ b/arch/arm64/kernel/process.c
    @@ -198,11 +198,9 @@ void __show_regs(struct pt_regs *regs)
    }

    show_regs_print_info(KERN_DEFAULT);
    - print_symbol("PC is at %s\n", instruction_pointer(regs));
    - print_symbol("LR is at %s\n", lr);
    - printk("pc : [<%016llx>] lr : [<%016llx>] pstate: %08llx\n",
    - regs->pc, lr, regs->pstate);
    - printk("sp : %016llx\n", sp);
    + print_symbol("pc : %s\n", regs->pc);
    + print_symbol("lr : %s\n", lr);
    + printk("sp : %016llx pstate : %08llx\n", sp, regs->pstate);
    for (i = top_reg; i >= 0; i--) {
    printk("x%-2d: %016llx ", i, regs->regs[i]);
    if (i % 2 == 0)
    --- a/arch/arm64/kernel/traps.c
    +++ b/arch/arm64/kernel/traps.c
    @@ -47,53 +47,9 @@ static const char *handler[]= {

    int show_unhandled_signals = 1;

    -/*
    - * Dump out the contents of some memory nicely...
    - */
    -static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
    - unsigned long top)
    -{
    - unsigned long first;
    - mm_segment_t fs;
    - int i;
    -
    - /*
    - * We need to switch to kernel mode so that we can use __get_user
    - * to safely read from kernel space.
    - */
    - fs = get_fs();
    - set_fs(KERNEL_DS);
    -
    - printk("%s%s(0x%016lx to 0x%016lx)\n", lvl, str, bottom, top);
    -
    - for (first = bottom & ~31; first < top; first += 32) {
    - unsigned long p;
    - char str[sizeof(" 12345678") * 8 + 1];
    -
    - memset(str, ' ', sizeof(str));
    - str[sizeof(str) - 1] = '\0';
    -
    - for (p = first, i = 0; i < 8 && p < top; i++, p += 4) {
    - if (p >= bottom && p < top) {
    - unsigned int val;
    - if (__get_user(val, (unsigned int *)p) == 0)
    - sprintf(str + i * 9, " %08x", val);
    - else
    - sprintf(str + i * 9, " ????????");
    - }
    - }
    - printk("%s%04lx:%s\n", lvl, first & 0xffff, str);
    - }
    -
    - set_fs(fs);
    -}
    -
    static void dump_backtrace_entry(unsigned long where, unsigned long stack)
    {
    - print_ip_sym(where);
    - if (in_exception_text(where))
    - dump_mem("", "Exception stack", stack,
    - stack + sizeof(struct pt_regs));
    + printk(" %pS\n", (void *)where);
    }

    static void __dump_instr(const char *lvl, struct pt_regs *regs)
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