Messages in this thread Patch in this message | | | Date | Fri, 20 Oct 2023 08:17:16 -0000 | From | "tip-bot2 for Ben Wolsieffer" <> | Subject | [tip: locking/core] futex: Don't include process in key on no-MMU |
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The following commit has been merged into the locking/core branch of tip:
Commit-ID: a684725f587b45955bfc0eadc5ebb36b6dbfb8b6 Gitweb: https://git.kernel.org/tip/a684725f587b45955bfc0eadc5ebb36b6dbfb8b6 Author: Ben Wolsieffer <ben.wolsieffer@hefring.com> AuthorDate: Thu, 19 Oct 2023 16:45:49 -04:00 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Fri, 20 Oct 2023 10:12:16 +02:00
futex: Don't include process in key on no-MMU
On no-MMU, all futexes are treated as private because there is no need to map a virtual address to physical to match the futex across processes. This doesn't quite work though, because private futexes include the current process's mm_struct as part of their key. This makes it impossible for one process to wake up a shared futex being waited on in another process.
This patch fixes this bug by excluding the mm_struct from the key. With a single address space, the futex address is already a unique key.
Fixes: 784bdf3bb694 ("futex: Assume all mappings are private on !MMU systems") Signed-off-by: Ben Wolsieffer <ben.wolsieffer@hefring.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Darren Hart <dvhart@infradead.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: André Almeida <andrealmeid@igalia.com> Link: https://lore.kernel.org/r/20231019204548.1236437-2-ben.wolsieffer@hefring.com --- kernel/futex/core.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/kernel/futex/core.c b/kernel/futex/core.c index ade7c73..52695c5 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -252,7 +252,17 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key, * but access_ok() should be faster than find_vma() */ if (!fshared) { - key->private.mm = mm; + /* + * On no-MMU, shared futexes are treated as private, therefore + * we must not include the current process in the key. Since + * there is only one address space, the address is a unique key + * on its own. + */ + if (IS_ENABLED(CONFIG_MMU)) + key->private.mm = mm; + else + key->private.mm = NULL; + key->private.address = address; return 0; }
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