From 4a000d96e29c05fa880ef99eeaec50a3f5a2ddcc Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Wed, 20 Mar 2019 10:55:29 -0400
Subject: [PATCH] pkey state is now preserved on fork for Linux 5.0+

This patch is going to be backported to stable kernels, so the check
could be expanded to allow recent enough stable kernel branches.
---
 h_malloc.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/h_malloc.c b/h_malloc.c
index 7b6854b..a502a5d 100644
--- a/h_malloc.c
+++ b/h_malloc.c
@@ -8,6 +8,7 @@
 #include <malloc.h>
 #include <pthread.h>
 #include <sys/mman.h>
+#include <sys/utsname.h>
 #include <unistd.h>
 
 #include "third_party/libdivide.h"
@@ -66,6 +67,7 @@ static union {
         struct region_metadata *regions[2];
 #ifdef USE_PKEY
         int metadata_pkey;
+        bool pkey_state_preserved_on_fork;
 #endif
     };
     char padding[PAGE_SIZE];
@@ -914,10 +916,12 @@ static void post_fork_child(void) {
     thread_unseal_metadata();
 
 #ifdef USE_PKEY
-    // disable sealing to work around kernel bug causing fork to lose the pkey setup
-    memory_protect_rw(&ro, sizeof(ro));
-    ro.metadata_pkey = -1;
-    memory_protect_ro(&ro, sizeof(ro));
+    if (!ro.pkey_state_preserved_on_fork) {
+        // disable sealing to work around kernel bug causing fork to lose the pkey setup
+        memory_protect_rw(&ro, sizeof(ro));
+        ro.metadata_pkey = -1;
+        memory_protect_ro(&ro, sizeof(ro));
+    }
 #endif
 
     mutex_init(&ro.region_allocator->lock);
@@ -952,6 +956,15 @@ COLD static void init_slow_path(void) {
 
 #ifdef USE_PKEY
     ro.metadata_pkey = pkey_alloc(0, 0);
+
+    // pkey state is not preserved on fork before Linux 5.0 unless the patch was backported
+    struct utsname uts;
+    if (uname(&uts) == 0) {
+        unsigned long version = strtoul(uts.release, NULL, 10);
+        if (version >= 5) {
+            ro.pkey_state_preserved_on_fork = true;
+        }
+    }
 #endif
 
     if (sysconf(_SC_PAGESIZE) != PAGE_SIZE) {