linux-kernel - [PATCH AUTOSEL 5.4 416/459] powerpc/mm: Don't log user reads to 0xffffffff

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Date:   Fri, 14 Feb 2020 11:01:06 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Christophe Leroy <christophe.leroy@....fr>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 5.4 416/459] powerpc/mm: Don't log user reads to 0xffffffff

From: Christophe Leroy <christophe.leroy@....fr>

[ Upstream commit 0f9aee0cb9da7db7d96f63cfa2dc5e4f1bffeb87 ]

Running vdsotest leaves many times the following log:

  [   79.629901] vdsotest[396]: User access of kernel address (ffffffff) - exploit attempt? (uid: 0)

A pointer set to (-1) is likely a programming error similar to
a NULL pointer and is not worth logging as an exploit attempt.

Don't log user accesses to 0xffffffff.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/0728849e826ba16f1fbd6fa7f5c6cc87bd64e097.1577087627.git.christophe.leroy@c-s.fr
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/mm/fault.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 9298905cfe74f..881a026a603a6 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -354,6 +354,9 @@ static void sanity_check_fault(bool is_write, bool is_user,
 	 * Userspace trying to access kernel address, we get PROTFAULT for that.
 	 */
 	if (is_user && address >= TASK_SIZE) {
+		if ((long)address == -1)
+			return;
+
 		pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
 				   current->comm, current->pid, address,
 				   from_kuid(&init_user_ns, current_uid()));
-- 
2.20.1