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* dll_init.cc (reserve_upto): Remove. 

(release_upto): Ditto.
(dll_list::reserve_space): New function to reserve space needed by DLL_LOAD
dlls early in the fork process.
(dll_list::load_after_fork): Rewrite to use recursion to track reservations it
makes while trying to make dlls land where they belong.
(dll_list::load_after_fork_impl): New function used by load_after_fork.
(dll_list::alloc): Initialize image base field.
* dll_init.h (dll_list::prefered_base): New field.
(dll_list::reserve_space): Declare new function.
(dll_list::load_after_fork): Declare new function.
* fork.cc (frok::child): call dll_list::reserve_space early, so we can retry if
it fails.
This commit is contained in:
Christopher Faylor 2011-05-30 16:09:29 +00:00
parent 7123c8b1fd
commit 6642f7daa3
4 changed files with 148 additions and 113 deletions
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17
winsup/cygwin/ChangeLog
View File

@ -1,3 +1,20 @@
2011-05-30 Ryan Johnson <ryan.johnson@cs.utoronto.ca>
* dll_init.cc (reserve_upto): Remove.
(release_upto): Ditto.
(dll_list::reserve_space): New function to reserve space needed by
DLL_LOAD dlls early in the fork process.
(dll_list::load_after_fork): Rewrite to use recursion to
track reservations it makes while trying to make dlls land where they
belong.
(dll_list::load_after_fork_impl): New function used by load_after_fork.
(dll_list::alloc): Initialize image base field.
* dll_init.h (dll_list::prefered_base): New field.
(dll_list::reserve_space): Declare new function.
(dll_list::load_after_fork): Declare new function.
* fork.cc (frok::child): call dll_list::reserve_space early, so we can
retry if it fails.
2011-05-30 Tor Perkins <cygwin@noid.net>
* fhandler_termios.cc (fhandler_termios::bg_check): Do not return EIO

235
winsup/cygwin/dll_init.cc
View File

@ -179,6 +179,7 @@ dll_list::alloc (HINSTANCE h, per_process *p, dll_type type)
if (d->modname)
d->modname++;
d->image_size = ((pefile*)h)->optional_hdr ()->SizeOfImage;
d->preferred_base = (void*) ((pefile*)h)->optional_hdr()->ImageBase;
d->type = type;
append (d);
if (type == DLL_LOAD)
@ -228,7 +229,7 @@ void dll_list::populate_deps (dll* d)
d->deps[d->ndeps++] = dep;
}
}
/* add one to differentiate no deps from unknown */
d->ndeps++;
}
@ -240,13 +241,13 @@ dll_list::topsort ()
/* Anything to do? */
if (!end)
return;
/* make sure we have all the deps available */
dll* d = &start;
while ((d = d->next))
if (!d->ndeps)
populate_deps (d);
/* unlink head and tail pointers so the sort can rebuild the list */
d = start.next;
start.next = end = NULL;
@ -290,7 +291,7 @@ dll_list::topsort_visit (dll* d, bool seek_tail)
ndeps (undone once the sort completes). */
if (seek_tail && d->next)
topsort_visit (d->next, true);
if (d->ndeps > 0)
{
d->ndeps = -d->ndeps;
@ -366,56 +367,6 @@ dll_list::init ()
#define A64K (64 * 1024)
/* Mark every memory address up to "here" as reserved. This may force
Windows NT to load a DLL in the next available, lowest slot. */
static void
reserve_upto (const PWCHAR name, DWORD here)
{
DWORD size;
MEMORY_BASIC_INFORMATION mb;
for (DWORD start = 0x10000; start < here; start += size)
if (!VirtualQuery ((void *) start, &mb, sizeof (mb)))
size = A64K;
else
{
size = A64K * ((mb.RegionSize + A64K - 1) / A64K);
start = A64K * (((DWORD) mb.BaseAddress + A64K - 1) / A64K);
if (start + size > here)
size = here - start;
if (mb.State == MEM_FREE &&
!VirtualAlloc ((void *) start, size, MEM_RESERVE, PAGE_NOACCESS))
api_fatal ("couldn't allocate memory %p(%d) for '%W' alignment, %E\n",
start, size, name);
}
}
/* Release all of the memory previously allocated by "upto" above.
Note that this may also free otherwise reserved memory. If that becomes
a problem, we'll have to keep track of the memory that we reserve above. */
static void
release_upto (const PWCHAR name, DWORD here)
{
DWORD size;
MEMORY_BASIC_INFORMATION mb;
for (DWORD start = 0x10000; start < here; start += size)
if (!VirtualQuery ((void *) start, &mb, sizeof (mb)))
size = 64 * 1024;
else
{
size = mb.RegionSize;
if (!(mb.State == MEM_RESERVE && mb.AllocationProtect == PAGE_NOACCESS
&& (((void *) start < cygheap->user_heap.base
|| (void *) start > cygheap->user_heap.top)
&& ((void *) start < (void *) cygheap
|| (void *) start
> (void *) ((char *) cygheap + CYGHEAPSIZE)))))
continue;
if (!VirtualFree ((void *) start, 0, MEM_RELEASE))
api_fatal ("couldn't release memory %p(%d) for '%W' alignment, %E\n",
start, size, name);
}
}
/* Reserve the chunk of free address space starting _here_ and (usually)
covering at least _dll_size_ bytes. However, we must take care not
@ -434,7 +385,7 @@ reserve_at (const PWCHAR name, DWORD here, DWORD dll_base, DWORD dll_size)
return 0;
size = mb.RegionSize;
// don't clobber the space where we want the dll to land
DWORD end = here + size;
DWORD dll_end = dll_base + dll_size;
@ -442,7 +393,7 @@ reserve_at (const PWCHAR name, DWORD here, DWORD dll_base, DWORD dll_size)
here = dll_end; // the dll straddles our left edge
else if (dll_base >= here && dll_base < end)
end = dll_base; // the dll overlaps partly or fully to our right
size = end - here;
if (!VirtualAlloc ((void *) here, size, MEM_RESERVE, PAGE_NOACCESS))
api_fatal ("couldn't allocate memory %p(%d) for '%W' alignment, %E\n",
@ -459,72 +410,130 @@ release_at (const PWCHAR name, DWORD here)
here, name);
}
/* Step 1: Reserve memory for all DLL_LOAD dlls. This is to prevent
anything else from taking their spot as we compensate for Windows
randomly relocating things.
NOTE: because we can't depend on LoadLibraryExW to do the right
thing, we have to do a vanilla VirtualAlloc instead. One possible
optimization might attempt a LoadLibraryExW first, in case it lands
in the right place, but then we have to find a way of tracking
which dlls ended up needing VirtualAlloc after all. */
void
dll_list::reserve_space ()
{
for (dll* d = dlls.istart (DLL_LOAD); d; d = dlls.inext ())
if (!VirtualAlloc (d->handle, d->image_size, MEM_RESERVE, PAGE_NOACCESS))
fork_info->abort ("address space needed by '%W' (%08lx) is already occupied",
d->modname, d->handle);
}
/* Reload DLLs after a fork. Iterates over the list of dynamically loaded
DLLs and attempts to load them in the same place as they were loaded in the
parent. */
void
dll_list::load_after_fork (HANDLE parent)
{
DWORD preferred_block = 0;
// moved to frok::child for performance reasons:
// dll_list::reserve_space();
for (dll *d = &dlls.start; (d = d->next) != NULL; )
if (d->type == DLL_LOAD)
for (int i = 0; i < 2; i++)
load_after_fork_impl (parent, dlls.istart (DLL_LOAD), 0);
}
static int const DLL_RETRY_MAX = 6;
void dll_list::load_after_fork_impl (HANDLE parent, dll* d, int retries)
{
/* Step 2: For each dll which did not map at its preferred base
address in the parent, try to coerce it to land at the same spot
as before. If not, unload it, reserve the memory around it, and
try again. Use recursion to remember blocked regions address
space so we can release them later.
We DONT_RESOLVE_DLL_REFERENCES at first in case the DLL lands in
the wrong spot;
NOTE: This step skips DLLs which loaded at their preferred
address in the parent because they should behave (we already
verified that their preferred address in the child is
available). However, this may fail on a Vista/Win7 machine with
ASLR active, because the ASLR base address will usually not equal
the preferred base recorded in the dll. In this case, we should
make the LoadLibraryExW call unconditional.
*/
for ( ; d; d = dlls.inext ())
if (d->handle != d->preferred_base)
{
/* See if the DLL will load in proper place. If not, unload it,
reserve the memory around it, and try again.
If this is the first attempt, we need to release the
dll's protective reservation from step 1
*/
if (!retries && !VirtualFree (d->handle, 0, MEM_RELEASE))
api_fatal ("unable to release protective reservation for %W (%08lx), %E",
d->modname, d->handle);
HMODULE h = LoadLibraryExW (d->name, NULL, DONT_RESOLVE_DLL_REFERENCES);
if (!h)
api_fatal ("unable to create interim mapping for %W, %E", d->name);
if (h != d->handle)
{
sigproc_printf ("%W loaded in wrong place: %08lx != %08lx",
d->modname, h, d->handle);
FreeLibrary (h);
DWORD reservation = reserve_at (d->modname, (DWORD) h,
(DWORD) d->handle, d->image_size);
if (!reservation)
api_fatal ("unable to block off %p to prevent %W from loading there",
h, d->modname);
if (retries < DLL_RETRY_MAX)
load_after_fork_impl (parent, d, retries+1);
else
fork_info->abort ("unable to remap %W to same address as parent (%08lx)",
d->modname, d->handle);
/* once the above returns all the dlls are mapped; release
the reservation and continue unwinding */
sigproc_printf ("releasing blocked space at %08lx", reservation);
release_at (d->modname, reservation);
return;
}
}
/* Step 3: try to load each dll for real after either releasing the
protective reservation (for well-behaved dlls) or unloading the
interim mapping (for rebased dlls) . The dll list is sorted in
dependency order, so we shouldn't pull in any additional dlls
outside our control.
It stinks that we can't invert the order of the initial LoadLibrary
and FreeLibrary since Microsoft documentation seems to imply that
should do what we want. However, once a library is loaded as
above, the second LoadLibrary will not execute its startup code
unless it is first unloaded. */
for (dll *d = dlls.istart (DLL_LOAD); d; d = dlls.inext ())
{
if (d->handle == d->preferred_base)
{
/* See if DLL will load in proper place. If so, free it and reload
it the right way.
It stinks that we can't invert the order of the initial LoadLibrary
and FreeLibrary since Microsoft documentation seems to imply that
should do what we want. However, once a library is loaded as
above, the second LoadLibrary will not execute its startup code
unless it is first unloaded. */
HMODULE h = LoadLibraryExW (d->name, NULL, DONT_RESOLVE_DLL_REFERENCES);
if (!h)
system_printf ("can't reload %W, %E", d->name);
else
{
FreeLibrary (h);
if (h == d->handle)
h = LoadLibraryW (d->name);
}
/* If we reached here on the second iteration of the for loop
then there is a lot of memory to release. */
if (i > 0)
{
release_upto (d->name, (DWORD) d->handle);
if (preferred_block)
release_at (d->name, preferred_block);
preferred_block = 0;
}
if (h == d->handle)
break; /* Success */
if (i > 0)
/* We tried once to relocate the dll and it failed. */
api_fatal ("unable to remap %W to same address as parent: %p != %p",
d->name, d->handle, h);
/* Dll loaded in the wrong place. Dunno why this happens but it
always seems to happen when there are multiple DLLs with the
same base address. In the "forked" process, the relocated DLL
may load at a different address. So, block all of the memory up
to the relocated load address and try again. */
reserve_upto (d->name, (DWORD) d->handle);
/* Also, if the DLL loaded at a higher address than wanted (probably
it's base address), reserve the memory at that address. This can
happen if it couldn't load at the preferred base in the parent, but
can in the child, due to differences in the load ordering.
Block memory at it's preferred address and try again. */
if ((DWORD) h > (DWORD) d->handle)
preferred_block = reserve_at (d->name, (DWORD) h,
(DWORD) d->handle, d->image_size);
if (!VirtualFree (d->handle, 0, MEM_RELEASE))
api_fatal ("unable to release protective reservation for %W (%08lx), %E",
d->modname, d->handle);
}
else
{
/* Free the library using our parent's handle: it's identical
to ours our we wouldn't have gotten this far */
if (!FreeLibrary (d->handle))
api_fatal ("unable to unload interim mapping of %W, %E", d->modname);
}
HMODULE h = LoadLibraryW (d->name);
if (!h)
api_fatal ("unable to map %W, %E", d->name);
if (h != d->handle)
api_fatal ("unable to map %W to same address as parent: %p != %p",
d->modname, d->handle, h);
}
}
struct dllcrt0_info

3
winsup/cygwin/dll_init.h
View File

@ -56,6 +56,7 @@ struct dll
dll** deps;
PWCHAR modname;
DWORD image_size;
void* preferred_base;
WCHAR name[1];
void detach ();
int init ();
@ -88,6 +89,8 @@ public:
void detach (void *);
void init ();
void load_after_fork (HANDLE);
void reserve_space ();
void load_after_fork_impl (HANDLE, dll* which, int retries);
dll *find_by_modname (const PWCHAR name);
void populate_all_deps ();
void populate_deps (dll* d);

6
winsup/cygwin/fork.cc
View File

@ -196,6 +196,12 @@ frok::child (volatile char * volatile here)
debug_printf ("child is running. pid %d, ppid %d, stack here %p",
myself->pid, myself->ppid, __builtin_frame_address (0));
/* NOTE: Logically this belongs in dll_list::load_after_fork, but by
doing it here, before the first sync_with_parent, we can exploit
the existing retry mechanism in hopes of getting a more favorable
address space layout next time. */
dlls.reserve_space ();
sync_with_parent ("after longjmp", true);
sigproc_printf ("hParent %p, load_dlls %d", hParent, load_dlls);