• Ruan Jinjie's avatar
    riscv: fix kprobe __user string arg print fault issue · 99a670b2
    Ruan Jinjie authored
    On riscv qemu platform, when add kprobe event on do_sys_open() to show
    filename string arg, it just print fault as follow:
    
    echo 'p:myprobe do_sys_open dfd=$arg1 filename=+0($arg2):string flags=$arg3
    mode=$arg4' > kprobe_events
    
    bash-166     [000] ...1.   360.195367: myprobe: (do_sys_open+0x0/0x84)
    dfd=0xffffffffffffff9c filename=(fault) flags=0x8241 mode=0x1b6
    
    bash-166     [000] ...1.   360.219369: myprobe: (do_sys_open+0x0/0x84)
    dfd=0xffffffffffffff9c filename=(fault) flags=0x8241 mode=0x1b6
    
    bash-191     [000] ...1.   360.378827: myprobe: (do_sys_open+0x0/0x84)
    dfd=0xffffffffffffff9c filename=(fault) flags=0x98800 mode=0x0
    
    As riscv do not select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE,
    the +0($arg2) addr is processed as a kernel address though it is a
    userspace address, cause the above filename=(fault) print. So select
    ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE to avoid the issue, after that the
    kprobe trace is ok as below:
    
    bash-166     [000] ...1.    96.767641: myprobe: (do_sys_open+0x0/0x84)
    dfd=0xffffffffffffff9c filename="/dev/null" flags=0x8241 mode=0x1b6
    
    bash-166     [000] ...1.    96.793751: myprobe: (do_sys_open+0x0/0x84)
    dfd=0xffffffffffffff9c filename="/dev/null" flags=0x8241 mode=0x1b6
    
    bash-177     [000] ...1.    96.962354: myprobe: (do_sys_open+0x0/0x84)
    dfd=0xffffffffffffff9c filename="/sys/kernel/debug/tracing/events/kprobes/"
    flags=0x98800 mode=0x0
    Signed-off-by: default avatarRuan Jinjie <ruanjinjie@huawei.com>
    Acked-by: default avatarBjörn Töpel <bjorn@rivosinc.com>
    Fixes: 0ebeea8c ("bpf: Restrict bpf_probe_read{, str}() only to archs where they work")
    Link: https://lore.kernel.org/r/20230504072910.3742842-1-ruanjinjie@huawei.comSigned-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
    99a670b2
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