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Cygwin: open_shared: try harder allocating a shared region 

For fixed regions (cygwin/user/myself/shared console), try fixed
address first.  Fallback to non-fixed region.  Don't even try fixed
address if the Cygwin DLL gets dynamically loaded.

For non-fixed regions, try to allocate in a loop within the area
from SHARED_REGIONS_ADDRESS_LOW to SHARED_REGIONS_ADDRESS_HIGH.

Fixes: 60675f1a7e ("Cygwin: decouple shared mem regions from Cygwin DLL")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2023-01-17 10:18:51 +01:00
parent 50cbbb1c0e
commit dc0fe7742b
2 changed files with 53 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

58
winsup/cygwin/mm/shared.cc
View File

@ -122,6 +122,7 @@ static uintptr_t region_address[] =
SHARED_CONSOLE_REGION_ADDRESS, /* SH_SHARED_CONSOLE */
0
};
static NO_COPY uintptr_t next_address = SHARED_REGIONS_ADDRESS_LOW;
void *
open_shared (const WCHAR *name, int n, HANDLE& shared_h, DWORD size,
@ -138,14 +139,9 @@ open_shared (const WCHAR *name, int n, HANDLE& shared_h, DWORD size,
{
WCHAR map_buf[MAX_PATH];
WCHAR *mapname = NULL;
void *shared;
void *shared = NULL;
void *addr;
if (m == SH_JUSTCREATE || m == SH_JUSTOPEN)
addr = NULL;
else
addr = (void *) region_address[m];
created = false;
if (!shared_h)
{
@ -170,14 +166,54 @@ open_shared (const WCHAR *name, int n, HANDLE& shared_h, DWORD size,
return NULL;
}
shared = MapViewOfFileEx (shared_h, FILE_MAP_READ | FILE_MAP_WRITE,
0, 0, 0, addr);
if (m < SH_TOTAL_SIZE && !dynamically_loaded)
{
/* Fixed regions. Don't do that if Cygwin gets dynamically loaded.
The process loading the DLL might be configured with High-Entropy
ASLR. Chances for collisions are pretty high.
Note that we don't actually *need* fixed addresses. The only
advantage is reproducibility to help /proc/<PID>/maps along. */
addr = (void *) region_address[m];
shared = MapViewOfFileEx (shared_h, FILE_MAP_READ | FILE_MAP_WRITE,
0, 0, 0, addr);
}
/* Also catch the unlikely case that a fixed region can't be mapped at the
fixed address. */
if (!shared)
{
/* Locate shared regions in the area between SHARED_REGIONS_ADDRESS_LOW
and SHARED_REGIONS_ADDRESS_HIGH, retrying until we have a slot.
Don't use MapViewOfFile3 (loader deadlock during fork. */
bool loop = false;
addr = (void *) next_address;
do
{
shared = MapViewOfFileEx (shared_h, FILE_MAP_READ | FILE_MAP_WRITE,
0, 0, 0, addr);
if (!shared)
{
next_address += wincap.allocation_granularity ();
if (next_address >= SHARED_REGIONS_ADDRESS_HIGH)
{
if (loop)
break;
next_address = SHARED_REGIONS_ADDRESS_LOW;
loop = true;
}
addr = (void *) next_address;
}
}
while (!shared);
}
if (!shared)
api_fatal ("MapViewOfFileEx '%W'(%p), %E. Terminating.", mapname, shared_h);
api_fatal ("MapViewOfFileEx '%W'(%p, size %u, m %d, created %d), %E. "
"Terminating.", mapname, shared_h, size, m, created);
debug_printf ("name %W, n %d, shared %p (wanted %p), h %p, m %d",
mapname, n, shared, addr, shared_h, m);
debug_printf ("name %W, shared %p (wanted %p), h %p, m %d, created %d",
mapname, shared, addr, shared_h, m, created);
return shared;
}

6
winsup/cygwin/release/3.4.4
View File

@ -16,3 +16,9 @@ Bug Fixes
- Fix vmstat(1) printing an error message on single core CPUs.
Addresses: https://cygwin.com/pipermail/cygwin/2023-January/252857.html
- Fix potential process termination during process initialization.
Most easily reproducible is the case of non-Cygwin processes running
with high-entropy VA enabled and loading the Cygwin DLL dynamically.
Addresses: https://cygwin.com/pipermail/cygwin/2023-January/252765.html
https://cygwin.com/pipermail/cygwin/2023-January/252865.html