Emit speculation barriers after ERETs
According to Linux commit 679db70801da9fda91d26caf13bf5b5ccc74e8e8
some ARM64 CPUs may speculate past an ERET. This could be used as part
of a side-channel attack.
To mitigate the issue, emit DSB/ISB barriers after every ERET.
Add a build step which dumps the generated ELF and check that this holds
for every ERET in the binary to prevent regressing.
Bug: 146490856
Change-Id: Idf1c2690637a7edb4a366d30fec26ed444069f5e
diff --git a/build/image/check_elf.py b/build/image/check_elf.py
new file mode 100644
index 0000000..cbc6454
--- /dev/null
+++ b/build/image/check_elf.py
@@ -0,0 +1,93 @@
+#!/usr/bin/env python
+#
+# Copyright 2019 The Hafnium Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+#!/usr/bin/env python
+"""Check ELF file for assembly-level regressions.
+
+Objdumps the given ELF file and detects known assembly patterns, checking for
+regressions on bugs such as CPU erratas. Throws an exception if a broken pattern
+is detected.
+"""
+
+import argparse
+import os
+import re
+import subprocess
+import sys
+
+HF_ROOT = os.path.dirname(os.path.dirname(os.path.dirname(__file__)))
+CLANG_ROOT = os.path.join(HF_ROOT, "prebuilts", "linux-x64", "clang")
+OBJDUMP = os.path.join(CLANG_ROOT, "bin", "llvm-objdump")
+
+def check_eret_speculation_barrier(objdump_stdout):
+ """
+ Some ARM64 CPUs speculatively execute instructions after ERET.
+ Check that every ERET is followed by DSB NSH and ISB.
+ """
+ found_eret = False
+
+ STATE_DEFAULT = 1
+ STATE_EXPECT_DSB_NSH = 2
+ STATE_EXPECT_ISB = 3
+
+ REGEX_ERET = re.compile(r"^\s*[0-9a-f]+:\s*e0 03 9f d6\s+eret$")
+ REGEX_DSB_NSH = re.compile(r"^\s*[0-9a-f]+:\s*9f 37 03 d5\s*dsb\s+nsh$")
+ REGEX_ISB = re.compile(r"^\s*[0-9a-f]+:\s*df 3f 03 d5\s+isb$")
+
+ state = STATE_DEFAULT
+ for line in objdump_stdout:
+ if state == STATE_DEFAULT:
+ if re.match(REGEX_ERET, line):
+ found_eret = True
+ state = STATE_EXPECT_DSB_NSH
+ elif state == STATE_EXPECT_DSB_NSH:
+ if re.match(REGEX_DSB_NSH, line):
+ state = STATE_EXPECT_ISB
+ else:
+ raise Exception("ERET not followed by DSB NSH")
+ elif state == STATE_EXPECT_ISB:
+ if re.match(REGEX_ISB, line):
+ state = STATE_DEFAULT
+ else:
+ raise Exception("ERET not followed by ISB")
+
+ # Ensure that at least one instance was found, otherwise the regexes are
+ # probably wrong.
+ if not found_eret:
+ raise Exception("Could not find any ERET instructions")
+
+def Main():
+ parser = argparse.ArgumentParser()
+ parser.add_argument("input_elf",
+ help="ELF file to analyze")
+ parser.add_argument("stamp_file",
+ help="file to be touched if successful")
+ args = parser.parse_args()
+
+ objdump_stdout = subprocess.check_output([
+ OBJDUMP, "-d", args.input_elf ])
+ objdump_stdout = objdump_stdout.splitlines()
+
+ check_eret_speculation_barrier(objdump_stdout)
+
+ # Touch `stamp_file`.
+ with open(args.stamp_file, "w"):
+ pass
+
+ return 0
+
+if __name__ == "__main__":
+ sys.exit(Main())