linux-kernel - [PATCH] um: Fix kernel mode fault condition

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Date:	Sun,  9 Aug 2015 22:31:37 +0200
From:	Richard Weinberger <richard@....at>
To:	user-mode-linux-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org, Richard Weinberger <richard@....at>
Subject: [PATCH] um: Fix kernel mode fault condition

We have to exclude memory locations <= PAGE_SIZE from
the condition and let the kernel mode fault path catch it.
Otherwise a kernel NULL pointer exception will be reported
as a kernel user space access.

Fixes: d2313084e2c (um: Catch unprotected user memory access)
Signed-off-by: Richard Weinberger <richard@....at>
---
 arch/um/kernel/trap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 557232f..5610b18 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -220,7 +220,7 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
 		show_regs(container_of(regs, struct pt_regs, regs));
 		panic("Segfault with no mm");
 	}
-	else if (!is_user && address < TASK_SIZE) {
+	else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
 		show_regs(container_of(regs, struct pt_regs, regs));
 		panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
 		       address, ip);
-- 
1.8.4.5

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