From: Richard Weinberger <richard@nod.at>
Date: Sun, 9 Aug 2015 20:26:33 +0000 (+0200)
Subject: um: Fix kernel mode fault condition
X-Git-Tag: firefly_0821_release~176^2~901^2
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=56b88a3bf97a39d3f4f010509917b76a865a6dc8;p=firefly-linux-kernel-4.4.55.git

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@nod.at>
---

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index d8a9fce6ee2e..98783dd0fa2e 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);