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# HG changeset patch
# User Armin Rigo <arigo@tunes.org>
# Date 1424942568 -3600
# Node ID c7edb1e84eb3c29cac0674790cb4efcbcf1683b2
# Parent 95e0563201602a2e1a8d83cc95a6a70048dfeece
issue #177: workaround for some Linux kernels
diff --git a/c/malloc_closure.h b/c/malloc_closure.h
--- a/c/malloc_closure.h
+++ b/c/malloc_closure.h
@@ -14,6 +14,54 @@
# endif
#endif
+/* On PaX enable kernels that have MPROTECT enable we can't use PROT_EXEC.
+
+ This is, apparently, an undocumented change to ffi_prep_closure():
+ depending on the Linux kernel we're running on, we must give it a
+ mmap that is either PROT_READ|PROT_WRITE|PROT_EXEC or only
+ PROT_READ|PROT_WRITE. In the latter case, just trying to obtain a
+ mmap with PROT_READ|PROT_WRITE|PROT_EXEC would kill our process(!),
+ but in that situation libffi is fine with only PROT_READ|PROT_WRITE.
+ There is nothing in the libffi API to know that, though, so we have
+ to guess by parsing /proc/self/status. "Meh."
+ */
+#ifdef __linux__
+#include <stdlib.h>
+
+static int emutramp_enabled = -1;
+
+static int
+emutramp_enabled_check (void)
+{
+ char *buf = NULL;
+ size_t len = 0;
+ FILE *f;
+ int ret;
+ f = fopen ("/proc/self/status", "r");
+ if (f == NULL)
+ return 0;
+ ret = 0;
+
+ while (getline (&buf, &len, f) != -1)
+ if (!strncmp (buf, "PaX:", 4))
+ {
+ char emutramp;
+ if (sscanf (buf, "%*s %*c%c", &emutramp) == 1)
+ ret = (emutramp == 'E');
+ break;
+ }
+ free (buf);
+ fclose (f);
+ return ret;
+}
+
+#define is_emutramp_enabled() (emutramp_enabled >= 0 ? emutramp_enabled \
+ : (emutramp_enabled = emutramp_enabled_check ()))
+#else
+#define is_emutramp_enabled() 0
+#endif
+
+
/* 'allocate_num_pages' is dynamically adjusted starting from one
page. It grows by a factor of PAGE_ALLOCATION_GROWTH_RATE. This is
meant to handle both the common case of not needing a lot of pages,
@@ -77,9 +125,12 @@
if (item == NULL)
return;
#else
+ int prot = PROT_READ | PROT_WRITE | PROT_EXEC;
+ if (is_emutramp_enabled ())
+ prot &= ~PROT_EXEC;
item = (union mmaped_block *)mmap(NULL,
allocate_num_pages * _pagesize,
- PROT_READ | PROT_WRITE | PROT_EXEC,
+ prot,
MAP_PRIVATE | MAP_ANONYMOUS,
-1,
0);
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