diff options
| author | Ben Wolsieffer <ben.wolsieffer@hefring.com> | 2023-10-19 23:45:49 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2023-10-27 12:53:42 +0300 |
| commit | c73801ae4f22b390228ebf471d55668e824198b6 (patch) | |
| tree | 3ff2d2f1871b78a9f626c9457a421e3ea4343fe4 | |
| parent | 184fdf9fc7ae6ae7155768faa48fc609d1a24b7e (diff) | |
| download | linux-c73801ae4f22b390228ebf471d55668e824198b6.tar.xz | |
futex: Don't include process MM in futex 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.
Fix 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
| -rw-r--r-- | kernel/futex/core.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/futex/core.c b/kernel/futex/core.c index ade7c731972d..52695c59d041 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; } |