prctl: Disable prctl(PR_SET_MDWE) on parisc

systemd-254 tries to use prctl(PR_SET_MDWE) for it's MemoryDenyWriteExecute
functionality, but fails on parisc which still needs executable stacks in
certain combinations of gcc/glibc/kernel.

Disable prctl(PR_SET_MDWE) by returning -EINVAL for now on parisc, until
userspace has catched up.

Signed-off-by: Helge Deller <[email protected]>
Co-developed-by: Linus Torvalds <[email protected]>
Reported-by: Sam James <[email protected]>
Closes: https://github.com/systemd/systemd/issues/29775
Tested-by: Sam James <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Cc: <[email protected]> # v6.3+

diff --git a/kernel/sys.c b/kernel/sys.c
index 420d9cb9cc8e203f50014bb2ec564f6598d9869c..e219fcfa112d863eeef58381d04fd4bab16a1e32 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2394,6 +2394,10 @@ static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3,
        if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN))
                return -EINVAL;
 
+       /* PARISC cannot allow mdwe as it needs writable stacks */
+       if (IS_ENABLED(CONFIG_PARISC))
+               return -EINVAL;
+
        current_bits = get_current_mdwe();
        if (current_bits && current_bits != bits)
                return -EPERM; /* Cannot unset the flags */