Date: Wed, 19 Jul 2023 00:40:13 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 272585] calling mprotect in an mmap-ed stack can affect non-target pages Message-ID: <bug-272585-227@https.bugs.freebsd.org/bugzilla/>
next in thread | raw e-mail | index | archive | help
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D272585 Bug ID: 272585 Summary: calling mprotect in an mmap-ed stack can affect non-target pages Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: jfc@mit.edu Attachment #243475 text/plain mime type: Created attachment 243475 --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=3D243475&action= =3Dedit mmap-ed stack with an inaccessible gap If I call mmap with MAP_GROWSDOWN|MAP_STACK and use mprotect to mark the 32= nd page from the top inaccessible (PROT_NONE), lower addresses in the region a= lso become inaccessible. This is an odd thing to do, I agree, but it happened = in a real program. Put another way: I call mmap with stack hints and get pages 0-255. Before touching the memory I call mprotect(PROT_NONE) on page 224. Now pages 1-223 are also inaccessible. The target of mprotect has to be 32 pages down, not 31 or 33, at least with= my system's configuration. Perhaps 32 pages is the initial mapped size of a s= tack region and when the stack grows it clones the page attributes of the lowest address. I attached an example that crashes reading an address that should be valid.= It works on Mac OS (without the unsupported MAP_GROWSDOWN|MAP_STACK flags) and Linux. (This is simplified from a larger program that allocates a highly aligned 1= MB stack by mapping a larger region and using mprotect to install guard pages.= It is not the "right" way to do it when MAP_ALIGNED is available. The program= was written first on Linux which doesn't have that option.) Reproduced on 13.2-STABLE/amd64, 13.2-STABLE/aarch64, 14-CURRENT/amd64. --=20 You are receiving this mail because: You are the assignee for the bug.=
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-272585-227>