Messages in this thread | | | Date | Tue, 08 Nov 2011 12:01:18 -0800 | From | David Daney <> | Subject | Re: [PATCH 2/4] MIPS Kprobes: Deny probes on ll/sc instructions |
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On 11/08/2011 09:05 AM, Maneesh Soni wrote: > > From: Maneesh Soni<manesoni@cisco.com> > > Deny probes on ll/sc instructions for MIPS kprobes > > As ll/sc instruction are for atomic read-modify-write operations, allowing > probes on top of these insturctions is a bad idea. >
s/insturctions/instructions/
Not only is it a bad idea, it will probably make them fail 100% of the time.
It is also an equally bad idea to place a probe between any LL and SC instructions. How do you prevent that?
If you cannot prevent probes between LL and SC, why bother with this at all?
David Daney
> Signed-off-by: Victor Kamensky<kamensky@cisco.com> > Signed-off-by: Maneesh Soni<manesoni@cisco.com> > --- > arch/mips/kernel/kprobes.c | 31 +++++++++++++++++++++++++++++++ > 1 files changed, 31 insertions(+), 0 deletions(-) > > diff --git a/arch/mips/kernel/kprobes.c b/arch/mips/kernel/kprobes.c > index 9fb1876..0ab1a5f 100644 > --- a/arch/mips/kernel/kprobes.c > +++ b/arch/mips/kernel/kprobes.c > @@ -113,6 +113,30 @@ insn_ok: > return 0; > } > > +/* > + * insn_has_ll_or_sc function checks whether instruction is ll or sc > + * one; putting breakpoint on top of atomic ll/sc pair is bad idea; > + * so we need to prevent it and refuse kprobes insertion for such > + * instructions; cannot do much about breakpoint in the middle of > + * ll/sc pair; it is upto user to avoid those places > + */ > +static int __kprobes insn_has_ll_or_sc(union mips_instruction insn) > +{ > + int ret = 0; > + > + switch (insn.i_format.opcode) { > + case ll_op: > + case lld_op: > + case sc_op: > + case scd_op: > + ret = 1; > + break; > + default: > + break; > + } > + return ret; > +} > + > int __kprobes arch_prepare_kprobe(struct kprobe *p) > { > union mips_instruction insn; > @@ -121,6 +145,13 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p) > > insn = p->addr[0]; > > + if (insn_has_ll_or_sc(insn)) { > + pr_notice("Kprobes for ll and sc instructions are not" > + "supported\n"); > + ret = -EINVAL; > + goto out; > + } > + > if (insn_has_delayslot(insn)) { > pr_notice("Kprobes for branch and jump instructions are not" > "supported\n");
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