Messages in this thread | | | Date | Tue, 02 Jun 2015 06:51:31 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH 1/2] kprobes/x86: boost: Fix checking if there is enough room for a jump |
| |
On 2015/06/02 1:32, Eugene Shatokhin wrote: > Kprobes' "boost" feature allows to avoid single-stepping in some cases, > along with its overhead. It needs a relative jump placed in the insn > slot right after the instruction. So the length of the instruction plus > 5 (the length of the near relative unconditional jump) must not exceed > the length of the slot. > > However, the code currently checks if that sum is strictly less than > the length of the slot. So "boost" cannot be used for the instructions > of 10 bytes in size (with MAX_INSN_SIZE == 15), like > "movabs $0x45525f4b434f4c43,%rax" (48 b8 43 4c 4f 43 4b 5f 52 45), > "movl $0x1,0xf8dd(%rip)" (c7 05 dd f8 00 00 01 00 00 00), etc. > > This patch fixes that conditional.
Looks good to me,
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Thanks!
> > Signed-off-by: Eugene Shatokhin <eugene.shatokhin@rosalab.ru> > --- > arch/x86/kernel/kprobes/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > index 1deffe6..0a42b76 100644 > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -881,7 +881,7 @@ static void resume_execution(struct kprobe *p, struct pt_regs *regs, > > if (p->ainsn.boostable == 0) { > if ((regs->ip > copy_ip) && > - (regs->ip - copy_ip) + 5 < MAX_INSN_SIZE) { > + (regs->ip - copy_ip) + 5 <= MAX_INSN_SIZE) { > /* > * These instructions can be executed directly if it > * jumps back to correct address. >
-- Masami HIRAMATSU Linux Technology Research Center, System Productivity Research Dept. Center for Technology Innovation - Systems Engineering Hitachi, Ltd., Research & Development Group E-mail: masami.hiramatsu.pt@hitachi.com
| |