lkml.org 
[lkml]   [2020]   [Jul]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [for-next][PATCH 04/18] x86/ftrace: Do not jump to direct code in created trampolines
    On Thu, Jul 02, 2020 at 05:58:16PM -0400, Steven Rostedt wrote:

    > + /* No need to test direct calls on created trampolines */
    > + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
    > + /* NOP the jnz 1f; but make sure it's a 2 byte jnz */
    > + ip = trampoline + (jmp_offset - start_offset);
    > + if (WARN_ON(*(char *)ip != 0x75))
    > + goto fail;
    > + ret = copy_from_kernel_nofault(ip, ideal_nops[2], 2);

    I really don't get this paranoia, what's wrong with memcpy() ?

    > + if (ret < 0)
    > + goto fail;
    > + }

    How about something like this?

    --- a/arch/x86/kernel/ftrace.c
    +++ b/arch/x86/kernel/ftrace.c
    @@ -359,17 +359,11 @@ create_trampoline(struct ftrace_ops *ops
    npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);

    /* Copy ftrace_caller onto the trampoline memory */
    - ret = copy_from_kernel_nofault(trampoline, (void *)start_offset, size);
    - if (WARN_ON(ret < 0))
    - goto fail;
    -
    - ip = trampoline + size;
    + memcpy(trampoline, (void *)start_offset, size);

    /* The trampoline ends with ret(q) */
    - retq = (unsigned long)ftrace_stub;
    - ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE);
    - if (WARN_ON(ret < 0))
    - goto fail;
    + ip = trampoline + size;
    + memcpy(ip, text_gen_insn(RET_INSN_OPCODE, NULL, NULL), RET_INSN_SIZE);

    /* No need to test direct calls on created trampolines */
    if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
    @@ -377,9 +371,7 @@ create_trampoline(struct ftrace_ops *ops
    ip = trampoline + (jmp_offset - start_offset);
    if (WARN_ON(*(char *)ip != 0x75))
    goto fail;
    - ret = copy_from_kernel_nofault(ip, ideal_nops[2], 2);
    - if (ret < 0)
    - goto fail;
    + memcpy(ip, ideal_nops[2], 2);
    }

    /*
    \
     
     \ /
      Last update: 2020-07-03 10:11    [W:2.205 / U:0.044 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site