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    SubjectRe: [RFC PATCH 2/8] jump label v4 - x86: Introduce generic jump patching without stop_machine
    * Steven Rostedt (rostedt@goodmis.org) wrote:
    > On Tue, 2010-01-12 at 11:26 -0500, Jason Baron wrote:
    >
    > > +/**
    > > + * text_poke_fixup() -- cross-modifying kernel text with fixup address.
    > > + * @addr: Modifying address.
    > > + * @opcode: New instruction.
    > > + * @len: length of modifying bytes.
    > > + * @fixup: Fixup address.
    > > + *
    > > + * Note: You must backup replaced instructions before calling this,
    > > + * if you need to recover it.
    > > + * Note: Must be called under text_mutex.
    > > + */
    > > +void *__kprobes text_poke_fixup(void *addr, const void *opcode, size_t len,
    > > + void *fixup)
    > > +{
    > > + static const unsigned char int3_insn = BREAKPOINT_INSTRUCTION;
    > > + static const int int3_size = sizeof(int3_insn);
    > > +
    > > + /* Replacing 1 byte can be done atomically. */
    > > + if (unlikely(len <= 1))
    > > + return text_poke(addr, opcode, len);
    >
    > This part bothers me. The text_poke just writes over the text directly
    > (using a separate mapping). But if that memory is in the pipeline of
    > another CPU, I think this could cause a GPF.

    It looks like we are thinking along the same lines.

    I'm under the impression that I pointed out this exact same issue in the
    previous round of review a few weeks ago. Does this submission reflect
    the up-to-date state of this patch ?

    Thanks,

    Mathieu

    >
    > -- Steve
    >
    > > +
    > > + /* Preparing */
    > > + patch_fixup_addr = fixup;
    > > + wmb();
    > > + patch_fixup_from = (u8 *)addr + int3_size; /* IP address after int3 */
    > > +
    > > + /* Cap by an int3 */
    > > + text_poke(addr, &int3_insn, int3_size);
    > > + sync_core_all();
    > > +
    > > + /* Replace tail bytes */
    > > + text_poke((char *)addr + int3_size, (const char *)opcode + int3_size,
    > > + len - int3_size);
    > > + sync_core_all();
    > > +
    > > + /* Replace int3 with head byte */
    > > + text_poke(addr, opcode, int3_size);
    > > + sync_core_all();
    > > +
    > > + /* Cleanup */
    > > + patch_fixup_from = NULL;
    > > + wmb();
    > > + return addr;
    > > +}
    > > +
    >

    --
    Mathieu Desnoyers
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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