From b3a14db7637232d30c878cc1f1ad6d8037e81379 Mon Sep 17 00:00:00 2001
From: Shawn Anastasio <shawn@anastas.io>
Date: Tue, 15 Jan 2019 22:42:21 -0600
Subject: [PATCH] linux/seccomp-bpf: ppc64+glibc workaround in SIGSYS handler

Workaround for an apparent issue with glibc negating syscall
parameters. Observed on a ppc64le machine with glibc.
More investigation required.
---
 sandbox/linux/seccomp-bpf/trap.cc | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Index: chromium-128.0.6613.113/sandbox/linux/seccomp-bpf/trap.cc
===================================================================
--- chromium-128.0.6613.113.orig/sandbox/linux/seccomp-bpf/trap.cc
+++ chromium-128.0.6613.113/sandbox/linux/seccomp-bpf/trap.cc
@@ -236,6 +236,20 @@ void Trap::SigSys(int nr, LinuxSigInfo*
       SetIsInSigHandler();
     }
 
+#if defined(__powerpc64__)
+    // On ppc64+glibc, some syscalls seem to accidentally negate the first
+    // parameter which causes checks against it to fail. For now, manually
+    // negate them back.
+    // TODO(shawn@anastas.io): investigate this issue further
+    auto nr = SECCOMP_SYSCALL(ctx);
+    if (nr == __NR_openat || nr == __NR_mkdirat || nr == __NR_faccessat || nr == __NR_readlinkat ||
+        nr == __NR_renameat || nr == __NR_renameat2 || nr == __NR_newfstatat || nr == __NR_unlinkat) {
+        if (static_cast<int>(SECCOMP_PARM1(ctx)) > 0) {
+            SECCOMP_PARM1(ctx) = -SECCOMP_PARM1(ctx);
+        }
+    }
+#endif
+
     // Copy the seccomp-specific data into a arch_seccomp_data structure. This
     // is what we are showing to TrapFnc callbacks that the system call
     // evaluator registered with the sandbox.