68 lines
2.2 KiB
Diff
68 lines
2.2 KiB
Diff
From d46406088d28b038a0a0f7396d9621f431482f6a Mon Sep 17 00:00:00 2001
|
|
From: "Ryan C. Underwood" <nemesis@icequake.net>
|
|
Date: Sun, 18 Mar 2018 07:00:42 -0700
|
|
Subject: [PATCH 333/411] Fully allocate file backing writable maps (#389)
|
|
|
|
When ftruncate() is used on a filesystem supporting sparse files,
|
|
space in the file is not actually allocated. Then, when the file
|
|
is mmap'd and libffi writes to the mapping, SIGBUS is thrown to
|
|
the calling application. Instead, always fully allocate the file
|
|
that will back writable maps.
|
|
---
|
|
src/closures.c | 32 +++++++++++++++++++++++++++++++-
|
|
1 file changed, 31 insertions(+), 1 deletion(-)
|
|
|
|
diff --git a/src/closures.c b/src/closures.c
|
|
index 59ce828..15e6e0f 100644
|
|
--- a/src/closures.c
|
|
+++ b/src/closures.c
|
|
@@ -723,6 +723,36 @@ open_temp_exec_file (void)
|
|
return fd;
|
|
}
|
|
|
|
+/* We need to allocate space in a file that will be backing a writable
|
|
+ mapping. Several problems exist with the usual approaches:
|
|
+ - fallocate() is Linux-only
|
|
+ - posix_fallocate() is not available on all platforms
|
|
+ - ftruncate() does not allocate space on filesystems with sparse files
|
|
+ Failure to allocate the space will cause SIGBUS to be thrown when
|
|
+ the mapping is subsequently written to. */
|
|
+static int
|
|
+allocate_space (int fd, off_t offset, off_t len)
|
|
+{
|
|
+ static size_t page_size;
|
|
+
|
|
+ /* Obtain system page size. */
|
|
+ if (!page_size)
|
|
+ page_size = sysconf(_SC_PAGESIZE);
|
|
+
|
|
+ unsigned char buf[page_size];
|
|
+ memset (buf, 0, page_size);
|
|
+
|
|
+ while (len > 0)
|
|
+ {
|
|
+ off_t to_write = (len < page_size) ? len : page_size;
|
|
+ if (write (fd, buf, to_write) < to_write)
|
|
+ return -1;
|
|
+ len -= to_write;
|
|
+ }
|
|
+
|
|
+ return 0;
|
|
+}
|
|
+
|
|
/* Map in a chunk of memory from the temporary exec file into separate
|
|
locations in the virtual memory address space, one writable and one
|
|
executable. Returns the address of the writable portion, after
|
|
@@ -744,7 +774,7 @@ dlmmap_locked (void *start, size_t length, int prot, int flags, off_t offset)
|
|
|
|
offset = execsize;
|
|
|
|
- if (ftruncate (execfd, offset + length))
|
|
+ if (allocate_space (execfd, offset, length))
|
|
return MFAIL;
|
|
|
|
flags &= ~(MAP_PRIVATE | MAP_ANONYMOUS);
|
|
--
|
|
1.8.3.1
|
|
|