prctl: Disable prctl(PR_SET_MDWE) on parisc

[ Upstream commit 793838138c157d4c49f4fb744b170747e3dabf58 ]

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 <deller@gmx.de>
Co-developed-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Sam James <sam@gentoo.org>
Closes: https://github.com/systemd/systemd/issues/29775
Tested-by: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/all/875y2jro9a.fsf@gentoo.org/
Cc: <stable@vger.kernel.org> # v6.3+
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/sys.c b/kernel/sys.c
index 4a8073c..7a4ae6d 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2395,6 +2395,10 @@ 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 */