On 11/08/2011 09:05 AM, Maneesh Soni wrote:
From: Maneesh Soni<manesoni@xxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Maneesh Soni<manesoni@xxxxxxxxx>
---
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");
