From da0cb12f19838eec245d135b6d59f3fcfe1fa7d0 Mon Sep 17 00:00:00 2001
From: Christophe Leroy <christophe.leroy@csgroup.eu>
Date: Wed, 15 Sep 2021 16:12:24 +0200
Subject: [PATCH] powerpc/32s: Fix kuap_kernel_restore()
Git-commit: d93f9e23744b7bf11a98b2ddb091d129482ae179
Patch-mainline: v5.15-rc5
References: stable-5.14.12
[ Upstream commit d93f9e23744b7bf11a98b2ddb091d129482ae179 ]
At interrupt exit, kuap_kernel_restore() calls kuap_unlock() with the
value contained in regs->kuap. However, when regs->kuap contains
0xffffffff it means that KUAP was not unlocked so calling kuap_unlock()
is unrelevant and results in jeopardising the contents of kernel space
segment registers.
So check that regs->kuap doesn't contain KUAP_NONE before calling
kuap_unlock(). In the meantime it also means that if KUAP has not
been correcly locked back at interrupt exit, it must be locked
before continuing. This is done by checking the content of
current->thread.kuap which was returned by kuap_get_and_assert_locked()
Fixes: 16132529cee5 ("powerpc/32s: Rework Kernel Userspace Access Protection")
Reported-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0d0c4d0f050a637052287c09ba521bad960a2790.1631715131.git.christophe.leroy@csgroup.eu
Signed-off-by: Sasha Levin <sashal@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
arch/powerpc/include/asm/book3s/32/kup.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
index d4b145b279f6..9f38040f0641 100644
--- a/arch/powerpc/include/asm/book3s/32/kup.h
+++ b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -136,6 +136,14 @@ static inline void kuap_kernel_restore(struct pt_regs *regs, unsigned long kuap)
if (kuap_is_disabled())
return;
+ if (unlikely(kuap != KUAP_NONE)) {
+ current->thread.kuap = KUAP_NONE;
+ kuap_lock(kuap, false);
+ }
+
+ if (likely(regs->kuap == KUAP_NONE))
+ return;
+
current->thread.kuap = regs->kuap;
kuap_unlock(regs->kuap, false);
--
2.26.2