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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.16 0839/1017] lib/test_lockup: fix kernel pointer check for separate address spaces
Date:   Tue,  5 Apr 2022 09:29:12 +0200
Message-Id: <20220405070419.145775392@linuxfoundation.org>
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From: Arnd Bergmann <arnd@arndb.de>

[ Upstream commit 5a06fcb15b43d1f7bf740c672950122331cb5655 ]

test_kernel_ptr() uses access_ok() to figure out if a given address
points to user space instead of kernel space. However on architectures
that set CONFIG_ALTERNATE_USER_ADDRESS_SPACE, a pointer can be valid
for both, and the check always fails because access_ok() returns true.

Make the check for user space pointers conditional on the type of
address space layout.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 lib/test_lockup.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/lib/test_lockup.c b/lib/test_lockup.c
index 6a0f329a794a..c3fd87d6c2dd 100644
--- a/lib/test_lockup.c
+++ b/lib/test_lockup.c
@@ -417,9 +417,14 @@ static bool test_kernel_ptr(unsigned long addr, int size)
 		return false;
 
 	/* should be at least readable kernel address */
-	if (access_ok((void __user *)ptr, 1) ||
-	    access_ok((void __user *)ptr + size - 1, 1) ||
-	    get_kernel_nofault(buf, ptr) ||
+	if (!IS_ENABLED(CONFIG_ALTERNATE_USER_ADDRESS_SPACE) &&
+	    (access_ok((void __user *)ptr, 1) ||
+	     access_ok((void __user *)ptr + size - 1, 1))) {
+		pr_err("user space ptr invalid in kernel: %#lx\n", addr);
+		return true;
+	}
+
+	if (get_kernel_nofault(buf, ptr) ||
 	    get_kernel_nofault(buf, ptr + size - 1)) {
 		pr_err("invalid kernel ptr: %#lx\n", addr);
 		return true;
-- 
2.34.1