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authorMarcin Nowakowski <marcin.nowakowski@imgtec.com>2016-09-30 12:33:46 +0300
committerRalf Baechle <ralf@linux-mips.org>2016-10-06 18:37:40 +0300
commitd05c513069f15be5de766026a4192998688ffff1 (patch)
tree7948594b560af72ed535a41cc567de4235562ff8 /arch/mips/kernel/branch.c
parente3031b32840c1bee228c58bb284ebc05f97249c7 (diff)
downloadlinux-d05c513069f15be5de766026a4192998688ffff1.tar.xz
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>
Diffstat (limited to 'arch/mips/kernel/branch.c')
-rw-r--r--arch/mips/kernel/branch.c34
1 files changed, 34 insertions, 0 deletions
diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index f5c68483c98e..12c718181e5e 100644
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -866,3 +866,37 @@ unaligned:
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 */