MIPS Kprobes: Deny probes on ll/sc instructions

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>
Cc: David Daney <david.daney@cavium.com>
Cc: ananth@in.ibm.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2912/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/arch/mips/kernel/kprobes.c b/arch/mips/kernel/kprobes.c
index 9fb1876cb0bd..0ab1a5ff1049 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");