https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=8adc45fdece5d8ea8017e635575562b76c4e9bcd
commit 8adc45fdece5d8ea8017e635575562b76c4e9bcd Author: Ken Brown <[email protected]> Date: Fri Dec 27 10:10:06 2024 -0500 Cygwin: mmap: fix mmap_is_attached_or_noreserve This commit fixes two problems. The first is that mmap_is_attached_or_noreserve would sometimes call VirtualAlloc with MEM_COMMIT on address ranges that were not known to have MEM_RESERVE status. These calls could fail, causing SIGBUS to be raised incorrectly. See https://cygwin.com/pipermail/cygwin-developers/2024-December/012725.html for details. Fix this by calling VirtualAlloc only on the part of the address range that's contained in the current mmap_record. The second problem is that the code would sometimes break out of the main loop without knowing whether attached mappings still occur later in the mmap_list. This could cause SIGBUS to not be raised when it should be. Fix this by using "continue" rather than "break". For efficiency, introduce a boolean variable "nocover" that's set to true if we discover that the address range cannot be covered by noreserve mmap regions. Addresses: https://cygwin.com/pipermail/cygwin-developers/2024-December/012725.html Fixes: 70e476d27be8 ("* include/cygwin/version.h: Bump DLL version to 1.7.0") Signed-off-by: Ken Brown <[email protected]> Diff: --- winsup/cygwin/mm/mmap.cc | 51 ++++++++++++++++++++++++++---------------------- 1 file changed, 28 insertions(+), 23 deletions(-) diff --git a/winsup/cygwin/mm/mmap.cc b/winsup/cygwin/mm/mmap.cc index 13418d782..741f12228 100644 --- a/winsup/cygwin/mm/mmap.cc +++ b/winsup/cygwin/mm/mmap.cc @@ -738,18 +738,18 @@ is_mmapped_region (caddr_t start_addr, caddr_t end_address) /* This function is called from exception_handler when a segmentation violation has occurred. It should also be called from all Cygwin - functions that want to support passing noreserve mmap page addresses - to Windows system calls. In that case, it should be called only after - a system call indicates that the application buffer passed had an - invalid virtual address to avoid any performance impact in non-noreserve - cases. + functions that want to support passing noreserve (anonymous) mmap + page addresses to Windows system calls. In that case, it should be + called only after a system call indicates that the application + buffer passed had an invalid virtual address to avoid any + performance impact in non-noreserve cases. Check if the address range is all within noreserve mmap regions. If so, call VirtualAlloc to commit the pages and return MMAP_NORESERVE_COMMITED - on success. If the page has __PROT_ATTACH (SUSv3 memory protection - extension), or if VirtualAlloc fails, return MMAP_RAISE_SIGBUS. - Otherwise, return MMAP_NONE if the address range is not covered by an - attached or noreserve map. + on success. If some page in the address range has __PROT_ATTACH + (SUSv3 memory protection extension), or if VirtualAlloc fails, + return MMAP_RAISE_SIGBUS. Otherwise, return MMAP_NONE if the + address range is not covered by noreserve maps. On MAP_NORESERVE_COMMITED, the exeception handler should return 0 to allow the application to retry the memory access, or the calling Cygwin @@ -768,12 +768,16 @@ mmap_is_attached_or_noreserve (void *addr, size_t len) len += ((caddr_t) addr - start_addr); len = roundup2 (len, pagesize); - if (map_list == NULL) - goto out; - mmap_record *rec; caddr_t u_addr; SIZE_T u_len; + /* nocover is set to true if we discover that our address range + cannot be covered by noreserve mmap regions. */ + bool nocover = false; + size_t remaining = len; + + if (map_list == NULL) + goto out; LIST_FOREACH (rec, &map_list->recs, mr_next) { @@ -784,23 +788,24 @@ mmap_is_attached_or_noreserve (void *addr, size_t len) ret = MMAP_RAISE_SIGBUS; break; } - if (!rec->noreserve ()) - break; - - size_t commit_len = u_len - (start_addr - u_addr); - if (commit_len > len) - commit_len = len; + if (nocover || !rec->noreserve ()) + { + /* We need to continue in case we encounter an attached mmap + later in the list. */ + nocover = true; + continue; + } - if (!VirtualAlloc (start_addr, commit_len, MEM_COMMIT, - rec->gen_protect ())) + /* The interval determined by u_addr and u_len is the part of + our address range contained in the mmap region of rec. */ + if (!VirtualAlloc (u_addr, u_len, MEM_COMMIT, rec->gen_protect ())) { ret = MMAP_RAISE_SIGBUS; break; } - start_addr += commit_len; - len -= commit_len; - if (!len) + remaining -= u_len; + if (!remaining) { ret = MMAP_NORESERVE_COMMITED; break;
