Messages in this thread | | | Date | Tue, 02 Jun 2015 06:58:12 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH 2/2] kprobes/x86: Use 16 bytes for each instruction slot again |
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On 2015/06/02 1:32, Eugene Shatokhin wrote: > Commit 91e5ed49fca0 ("x86/asm/decoder: Fix and enforce max instruction > size in the insn decoder") has changed MAX_INSN_SIZE from 16 to 15 bytes > on x86. > > As a side effect, the slots Kprobes use to store the instructions became > 1 byte shorter. This is unfortunate because, for example, the Kprobes' > "boost" feature can not be used now for the instructions of length 11, > like a quite common kind of MOV: > * movq $0xffffffffffffffff,-0x3fe8(%rax) (48 c7 80 18 c0 ff ff ff ff ff ff) > * movq $0x0,0x88(%rdi) (48 c7 87 88 00 00 00 00 00 00 00) > and so on. > > This patch makes the insn slots 16 bytes long, like they were before while > keeping MAX_INSN_SIZE intact. > > Other tools may benefit from this change as well. > > Signed-off-by: Eugene Shatokhin <eugene.shatokhin@rosalab.ru> > --- > arch/x86/include/asm/kprobes.h | 1 + > arch/x86/kernel/kprobes/core.c | 2 +- > kernel/kprobes.c | 8 ++++++-- > 3 files changed, 8 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h > index 4421b5d..f3f0b4e 100644 > --- a/arch/x86/include/asm/kprobes.h > +++ b/arch/x86/include/asm/kprobes.h > @@ -27,6 +27,7 @@ > #include <asm/insn.h> > > #define __ARCH_WANT_KPROBES_INSN_SLOT
Please add a comment here why the slot size is bigger than MAX_INSN_SIZE.
> +#define KPROBE_INSN_SLOT_SIZE 16
And make sure that KPROBE_INSN_SLOT_SIZE >= MAX_INSN_SIZE.
Other parts are OK for me.
Thanks!
> > struct pt_regs; > struct kprobe; > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > index 0a42b76..1067f90 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 <= KPROBE_INSN_SLOT_SIZE) { > /* > * These instructions can be executed directly if it > * jumps back to correct address. > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index c90e417..1dc074d 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -57,7 +57,6 @@ > #define KPROBE_HASH_BITS 6 > #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS) > > - > /* > * Some oddball architectures like 64bit powerpc have function descriptors > * so this must be overridable. > @@ -90,6 +89,11 @@ static raw_spinlock_t *kretprobe_table_lock_ptr(unsigned long hash) > static LIST_HEAD(kprobe_blacklist); > > #ifdef __ARCH_WANT_KPROBES_INSN_SLOT > + > +#ifndef KPROBE_INSN_SLOT_SIZE > +#define KPROBE_INSN_SLOT_SIZE MAX_INSN_SIZE > +#endif > + > /* > * kprobe->ainsn.insn points to the copy of the instruction to be > * single-stepped. x86_64, POWER4 and above have no-exec support and > @@ -135,7 +139,7 @@ struct kprobe_insn_cache kprobe_insn_slots = { > .alloc = alloc_insn_page, > .free = free_insn_page, > .pages = LIST_HEAD_INIT(kprobe_insn_slots.pages), > - .insn_size = MAX_INSN_SIZE, > + .insn_size = KPROBE_INSN_SLOT_SIZE, > .nr_garbage = 0, > }; > static int collect_garbage_slots(struct kprobe_insn_cache *c); >
-- 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
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