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[PATCH 2/4] MIPS Kprobes: Deny probes on ll/sc instructions

To: Ralf Baechle <ralf@linux-mips.org>
Subject: [PATCH 2/4] MIPS Kprobes: Deny probes on ll/sc instructions
From: Maneesh Soni <manesoni@cisco.com>
Date: Tue, 8 Nov 2011 22:35:35 +0530
Cc: David Daney <david.daney@cavium.com>, ananth@in.ibm.com, kamensky@cisco.com, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org
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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.

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");
-- 
1.7.1


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