• Sandeepa Prabhu's avatar
    arm64: Kprobes with single stepping support · 2dd0e8d2
    Sandeepa Prabhu authored
    Add support for basic kernel probes(kprobes) and jump probes
    (jprobes) for ARM64.
    
    Kprobes utilizes software breakpoint and single step debug
    exceptions supported on ARM v8.
    
    A software breakpoint is placed at the probe address to trap the
    kernel execution into the kprobe handler.
    
    ARM v8 supports enabling single stepping before the break exception
    return (ERET), with next PC in exception return address (ELR_EL1). The
    kprobe handler prepares an executable memory slot for out-of-line
    execution with a copy of the original instruction being probed, and
    enables single stepping. The PC is set to the out-of-line slot address
    before the ERET. With this scheme, the instruction is executed with the
    exact same register context except for the PC (and DAIF) registers.
    
    Debug mask (PSTATE.D) is enabled only when single stepping a recursive
    kprobe, e.g.: during kprobes reenter so that probed instruction can be
    single stepped within the kprobe handler -exception- context.
    The recursion depth of kprobe is always 2, i.e. upon probe re-entry,
    any further re-entry is prevented by not calling handlers and the case
    counted as a missed kprobe).
    
    Single stepping from the x-o-l slot has a drawback for PC-relative accesses
    like branching and symbolic literals access as the offset from the new PC
    (slot address) may not be ensured to fit in the immediate value of
    the opcode. Such instructions need simulation, so reject
    probing them.
    
    Instructions generating exceptions or cpu mode change are rejected
    for probing.
    
    Exclusive load/store instructions are rejected too.  Additionally, the
    code is checked to see if it is inside an exclusive load/store sequence
    (code from Pratyush).
    
    System instructions are mostly enabled for stepping, except MSR/MRS
    accesses to "DAIF" flags in PSTATE, which are not safe for
    probing.
    
    This also changes arch/arm64/include/asm/ptrace.h to use
    include/asm-generic/ptrace.h.
    
    Thanks to Steve Capper and Pratyush Anand for several suggested
    Changes.
    Signed-off-by: default avatarSandeepa Prabhu <sandeepa.s.prabhu@gmail.com>
    Signed-off-by: default avatarDavid A. Long <dave.long@linaro.org>
    Signed-off-by: default avatarPratyush Anand <panand@redhat.com>
    Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
    Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    2dd0e8d2
Kconfig 30.3 KB