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authorPhilip Sanderson <philip.k.sanderson@gmail.com>2011-01-20 21:37:28 -0600
committerRusty Russell <rusty@rustcorp.com.au>2011-01-20 21:37:29 +1030
commit5230ff0cccb0611830bb02b097535868df02752a (patch)
tree7d1345e1ede12e2fd85918c9944fe929017cde6b /Documentation
parent8aeb36e8f6d7eaa9cafc970b700414205743b258 (diff)
downloadlinux-linaro-android-5230ff0cccb0611830bb02b097535868df02752a.tar.gz
lguest: example launcher to use guard pages, drop PROT_EXEC, fix limit logic
PROT_EXEC seems to be completely unnecessary (as the lguest binary never executes there), and will allow it to work with SELinux (and more importantly, PaX :-) as they can/do forbid writable and executable mappings. Also, map PROT_NONE guard pages at start and end of guest memory for extra paranoia. I changed the length check to addr + size > guest_limit because >= is wrong (addr of 0, size of getpagesize() with a guest_limit of getpagesize() would false positive). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/lguest/lguest.c23
1 files changed, 15 insertions, 8 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index f64b85bcd6d..d9da7e14853 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -301,20 +301,27 @@ static void *map_zeroed_pages(unsigned int num)
/*
* We use a private mapping (ie. if we write to the page, it will be
- * copied).
+ * copied). We allocate an extra two pages PROT_NONE to act as guard
+ * pages against read/write attempts that exceed allocated space.
*/
- addr = mmap(NULL, getpagesize() * num,
- PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, fd, 0);
+ addr = mmap(NULL, getpagesize() * (num+2),
+ PROT_NONE, MAP_PRIVATE, fd, 0);
+
if (addr == MAP_FAILED)
err(1, "Mmapping %u pages of /dev/zero", num);
+ if (mprotect(addr + getpagesize(), getpagesize() * num,
+ PROT_READ|PROT_WRITE) == -1)
+ err(1, "mprotect rw %u pages failed", num);
+
/*
* One neat mmap feature is that you can close the fd, and it
* stays mapped.
*/
close(fd);
- return addr;
+ /* Return address after PROT_NONE page */
+ return addr + getpagesize();
}
/* Get some more pages for a device. */
@@ -346,7 +353,7 @@ static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
* done to it. This allows us to share untouched memory between
* Guests.
*/
- if (mmap(addr, len, PROT_READ|PROT_WRITE|PROT_EXEC,
+ if (mmap(addr, len, PROT_READ|PROT_WRITE,
MAP_FIXED|MAP_PRIVATE, fd, offset) != MAP_FAILED)
return;
@@ -576,10 +583,10 @@ static void *_check_pointer(unsigned long addr, unsigned int size,
unsigned int line)
{
/*
- * We have to separately check addr and addr+size, because size could
- * be huge and addr + size might wrap around.
+ * Check if the requested address and size exceeds the allocated memory,
+ * or addr + size wraps around.
*/
- if (addr >= guest_limit || addr + size >= guest_limit)
+ if ((addr + size) > guest_limit || (addr + size) < addr)
errx(1, "%s:%i: Invalid address %#lx", __FILE__, line, addr);
/*
* We return a pointer for the caller's convenience, now we know it's