MIPS: tracing: disable uprobe/kprobe on compact branch instructions
Current instruction decoder for uprobe/kprobe handler only handles
branches with delay slots. For compact branches the behaviour is rather
unpredictable - and depending on the encoding of a compact branch
instruction may result in one (or more) of:
- executing an instruction that follows a branch which wasn't in a delay
slot and shouldn't have been executed
- incorrectly emulating a branch leading to a jump to a wrong location
- unexpected branching out of the single-stepped code and never reaching
the breakpoint that should terminate the probe handler
Results of these actions are generally unpredictable, but can end up
with a probed application or kernel crash, so disable placing probes on
compact branches until they are handled properly.
Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14336/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index f5c6848..12c7181 100644
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -866,3 +866,37 @@
force_sig(SIGBUS, current);
return -EFAULT;
}
+
+#if (defined CONFIG_KPROBES) || (defined CONFIG_UPROBES)
+
+int __insn_is_compact_branch(union mips_instruction insn)
+{
+ if (!cpu_has_mips_r6)
+ return 0;
+
+ switch (insn.i_format.opcode) {
+ case blezl_op:
+ case bgtzl_op:
+ case blez_op:
+ case bgtz_op:
+ /*
+ * blez[l] and bgtz[l] opcodes with non-zero rt
+ * are MIPS R6 compact branches
+ */
+ if (insn.i_format.rt)
+ return 1;
+ break;
+ case bc6_op:
+ case balc6_op:
+ case pop10_op:
+ case pop30_op:
+ case pop66_op:
+ case pop76_op:
+ return 1;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(__insn_is_compact_branch);
+
+#endif /* CONFIG_KPROBES || CONFIG_UPROBES */