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SubjectRe: [RFC PATCH tip/master V2 4/8] kprobes/x86: Do not modify singlestep buffer while resuming

* Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Do not modify singlestep execution buffer (kprobe.ainsn.insn)
> while resuming from single-stepping, instead, modifies
> the buffer to add a jump back instruction at preparing
> buffer.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> arch/x86/kernel/kprobes/core.c | 42 +++++++++++++++++++---------------------
> 1 file changed, 20 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 6327f95..ea3b8e5 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -399,23 +399,36 @@ int __copy_instruction(u8 *dest, u8 *src)
> return length;
> }
>
> +/* Prepare reljump right after instruction to boost */
> +static void prepare_boost(struct kprobe *p, int length)
> +{
> + if (can_boost(p->ainsn.insn, p->addr) &&
> + MAX_INSN_SIZE - length >= RELATIVEJUMP_SIZE) {
> + /*
> + * These instructions can be executed directly if it
> + * jumps back to correct address.
> + */
> + synthesize_reljump((void *)p->ainsn.insn + length,
> + (void *)p->addr + length);
> + p->ainsn.boostable = 1;
> + } else
> + p->ainsn.boostable = -1;

Those imbalanced curly braces are not proper kernel style.

Also, is the (void *) cast required? arch.insns ought to be void * already, right?
(I haven't checking whether that's true for all architectures.)

Btw., the original code had the curly braces right:

> - if (p->ainsn.boostable == 0) {
> - if ((regs->ip > copy_ip) &&
> - (regs->ip - copy_ip) + 5 < MAX_INSN_SIZE) {
> - /*
> - * These instructions can be executed directly if it
> - * jumps back to correct address.
> - */
> - synthesize_reljump((void *)regs->ip,
> - (void *)orig_ip + (regs->ip - copy_ip));
> - p->ainsn.boostable = 1;
> - } else {
> - p->ainsn.boostable = -1;
> - }
> - }

Thanks,

Ingo

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