linux-kernel - [PATCH v1 3/5] powerpc/fault: Reorder tests in bad_kernel

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Message-Id: <ef827b73770a7b155079393f8d8430e10a99ec94.1596734104.git.christophe.leroy@csgroup.eu>
Date:   Thu,  6 Aug 2020 17:15:30 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, npiggin@...il.com
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v1 3/5] powerpc/fault: Reorder tests in bad_kernel_fault()

Check address earlier to simplify the following test.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/mm/fault.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 9ef9ee244f72..525e0c2b5406 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -210,17 +210,17 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
 		return true;
 	}
 
-	if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) &&
+	// Kernel fault on kernel address is bad
+	if (address >= TASK_SIZE)
+		return true;
+
+	if (!is_exec && (error_code & DSISR_PROTFAULT) &&
 	    !search_exception_tables(regs->nip)) {
 		pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n",
 				    address,
 				    from_kuid(&init_user_ns, current_uid()));
 	}
 
-	// Kernel fault on kernel address is bad
-	if (address >= TASK_SIZE)
-		return true;
-
 	// Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad
 	if (!search_exception_tables(regs->nip))
 		return true;
-- 
2.25.0