From b44fd97af6999e032f71e9e7c265b43163cb4052 Mon Sep 17 00:00:00 2001
From: Christian Poveda <christianpoveda@protonmail.com>
Date: Mon, 19 Aug 2019 10:43:09 -0500
Subject: [PATCH] Use host's rng when communication is enabled

---
 Cargo.toml     |  1 +
 src/helpers.rs | 13 +++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 644a3476a6d..1ab0580cc63 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -35,6 +35,7 @@ byteorder = { version = "1.1", features = ["i128"]}
 cargo_metadata = { version = "0.8", optional = true }
 directories = { version = "2.0", optional = true }
 rustc_version = { version = "0.2.3", optional = true }
+getrandom = "0.1.10"
 env_logger = "0.6"
 log = "0.4"
 shell-escape = "0.1.4"
diff --git a/src/helpers.rs b/src/helpers.rs
index c0e1ec2cd75..d134a19f4c2 100644
--- a/src/helpers.rs
+++ b/src/helpers.rs
@@ -97,9 +97,18 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             Align::from_bytes(1).unwrap()
         )?.expect("we already checked for size 0");
 
-        let rng = this.memory_mut().extra.rng.get_mut();
         let mut data = vec![0; len];
-        rng.fill_bytes(&mut data);
+
+        if this.machine.communicate {
+            // Fill the buffer using the host's rng.
+            getrandom::getrandom(&mut data).map_err(|err| {
+                InterpError::Unsupported(UnsupportedOpInfo::Unsupported(err.to_string()))
+            })?;
+        }
+        else {
+            let rng = this.memory_mut().extra.rng.get_mut();
+            rng.fill_bytes(&mut data);
+        }
 
         let tcx = &{this.tcx.tcx};
         this.memory_mut().get_mut(ptr.alloc_id)?.write_bytes(tcx, ptr, &data)